HomeMy WebLinkAboutStormwater Management Manual Lake Oswego
STORMWATER MANAGEMENT MANUAL
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GREGO
JUNE 2025
TABLE OF CONTENTS
1 Introduction 1
1.1 Purpose 2
1.2 SWMM History 2
1.3 Climate Change 2
1.4 Stormwater Effects 3
1.4.1 Water Quantity Effects 5
1.4.2 Hydromodification Effects 5
1.4.3 Water Quality Effects 6
1.5 Impaired Rivers and Streams 6
1.6 Document Hierarchy 9
2 Development Process 10
2.1 Plan Review 11
2.2 Construction Inspections 11
2.3 Post-Construction 11
2.4 Stormwater Facility Alterations 16
2.4.1 Restorations and Renovations 16
2.4.2 Replacements 16
2.4.3 Augmentation 16
3 Stormwater Thresholds 18
3.1 Project Class 18
3.1.1 Impervious Area Calculation 18
3.1.2 Small Projects 18
3.1.3 Large Projects 19
3.1.4 Transportation Projects 19
3.1.5 Dredge and Fill Projects 19
3.2 Project Exemptions and Variances 20
3.2.1 Exemptions 20
3.2.2 Variances 21
4 Submittals 22
4.1 Pre-Construction Submittals 22
4.1.1 Plan Submittals 22
ii
4.1.2 Report Submittals 25
4.2 Stormwater Plan Revisions 28
4.3 Post-Construction Submittals 29
4.3.1 Stormwater Facility Certification 29
4.3.2 DEQ Approval of Underground Injection Control Systems 29
4.3.3 Recorded Operations and Maintenance Plan 30
4.3.4 Pipe System Video 30
4.3.5 As-Built Drawings 30
5 Source Control 31
5.1.1 Outside Solid Material or Waste Storage Areas 31
5.1.2 Liquid Material or Waste Storage Areas 31
5.1.3 Covers 31
6 Site Assessment 32
6.1 Existing Drainage Patterns 32
6.2 Geotechnical Conditions 32
6.2.1 Soil Classification 32
6.2.2 Steep Slopes 35
6.2.3 Hydraulically-Restrictive Layers 35
6.2.4 Soil Fill 35
6.2.5 Contaminated Soil 35
6.3 Hydrology 35
6.3.1 Floodplains 35
6.3.2 Groundwater 37
6.3.3 Infiltration Tests 38
6.3.4 Groundwater Mounding Analysis 39
6.3.5 Post-Construction Infiltration Testing 39
6.4 Setbacks 39
6.4.1 Onsite Wastewater Systems 40
6.4.2 Constraints 40
7 Stormwater Facility Selection 41
7.1 Project Type 41
7.2 Facility Hierarchy 42
7.3 Onsite Retention 43
iii
7.4 Extended Filtration 43
7.5 Water-Quality Limited Waterways 43
7.5.1 Suspended Material 43
7.5.2 Phosphorous 44
7.5.3 Copper and Zinc 44
7.6 Capital Improvements and Public Improvements 44
7.7 Summary 44
8 Stormwater Modeling 46
8.1 Approved Models 46
8.1.1 Single-Event Models Santa Barbara Urban Hydrograph 46
8.1.2 Continuous Simulation Models 47
8.1.3 Prescriptive Sizing 47
8.2 Model Parameters 48
8.2.1 Curve Numbers 48
8.2.2 Time of Concentration 48
8.2.3 Infiltration rates 49
8.2.4 Orifices 49
8.3 Flow Control 49
8.3.1 Exemptions 49
8.3.2 Flow Control Procedure 50
8.4 Capacity Analyses 52
8.4.1 Downstream Analysis 52
8.4.2 Backwater Analysis 53
9 Stormwater Facility Design 54
9.1 General Design Standards 54
9.1.1 Vegetated Facilities 54
9.1.2 Underground Injection Controls 58
9.1.3 Regional Facilities 59
9.1.4 Proprietary Stormwater Treatment 60
9.2 Specific Design Standards 61
9.2.1 Drywells (Standard Detail SD1-02) 61
9.2.2 Permeable Pavement (Standard Detail SD9-09) 62
9.2.3 Pervious Pavers (Standard Detail SD9-10) 64
iv
9.2.4 Planters (Standard Details SD9-12 and SD9-13) 66
9.2.5 Ponds 67
9.2.6 Raingardens (Standard Details SD9-15 and SD9-16) 68
9.2.7 Sand Filter 69
9.2.8 Swale (Standard Details SD9-19 and SD9-20) 71
9.2.9 Trenches and Galleries (Standard Detail SD9-06) 72
9.2.10 Vegetated Filter Strips ((Standard Detail SD9-05) 73
9.2.11 Water-Quality Vaults 74
9.2.12 Wetlands, Constructed 75
10 Conveyance Design 76
10.1 Detention 76
10.2 Conveyance Structures 76
10.2.1 Alignment and Location 76
10.2.2 Private and Public System Connections 77
10.2.3 Stormline and Manholes 77
10.2.4 Catch Basins and Inlets 78
10.2.5 Ditches 78
10.2.6 Culverts and Bridges 78
10.3 Outfalls and Offsite Stormwater Discharges 79
10.4 Public Conveyance Extension 80
10.5 Easements 80
10.6 Encroachments 81
11 Maintenance of Stormwater Facilities 82
11.1 Operations and Maintenance Plans 82
11.2 Facility Access 82
11.3 Inspections 82
11.3.1 Inspection Records 83
11.3.2 City Inspections 83
11.3.3 Property Sale and Facility Ownership Transfer 83
11.4 Maintenance 83
11.4.1 Catch Basins 83
11.4.2 Detention Tanks and Vaults 84
11.4.3 Drywells, Infiltration Trenches, and Infiltration Galleries 84
v
11.4.4 Permeable Pavements and Pervious Pavers 84
11.4.5 Planters, Raingardens, and Swales 84
11.4.6 Ponds and Wetlands 85
11.4.7 Sand Filters 85
11.4.8 Vegetated Filter Strips 86
11.4.9 Wetlands 86
12 Erosion and Sediment Control 87
12.1 Regulatory Overview 87
12.1.1 Municipal Code 87
12.1.2 MS4 Permit 87
12.1.3 TMDL Implementation Plan 87
12.2 Erosion and Sediment Movement 88
12.2.1 Soil Type 88
12.2.2 Slope Gradient 88
12.2.3 Slope Length 89
12.2.4 Project Size and Timing 89
12.3 ESC Permits 89
12.3.1 ESC Plans 89
12.3.2 Certified Professionals 89
12.4 Erosion and Sediment Control Selection 90
12.4.1 Required Erosion and Sediment Controls 90
12.4.2 Construction Access and Parking 90
12.4.3 Sediment Control 91
12.4.4 Run-on Control 93
12.4.5 Dust Control 93
12.4.6 Stabilize Slopes and Disturbed Areas 93
12.4.7 Stockpile Areas 94
12.4.8 Source Control 94
12.4.9 Wet Weather Requirements 95
12.5 Pre-Construction 95
12.5.1 Schedules and Phasing 95
12.5.2 Weather Forecasts 96
12.5.3 Training 96
vi
12.6 Construction 96
12.6.1 Inspections and Inspection Logs 97
12.6.2 Significant Discharges 97
12.6.3 Modifications to Approved ESC Plans 98
12.6.4 Enforcement 98
12.6.5 Post Construction 98
13 Definitions 99
14 References 111
Appendix A Stormwater Report Template 113
Stormwater Report 114
Basic Stormwater Report 116
Appendix B Infiltration Test Log and Report Template 118
Infiltration Test Log 119
Infiltration Report 120
Appendix C Plant Selection and Approved Plant List 121
Appendix D Operations & Maintenance Template 141
Appendix E Simple Erosion and Sediment Control Template 142
vii
LIST OF TABLES
Table 1. Impaired Streams in Lake Oswego 7
Table 2. City Watersheds affected by TMDLs 8
Table 3. Project Requirements Based on Classification 19
Table 4. Performance Standards 41
Table 5. Stormwater Facility Hierarchy 42
Table 6. Approved Stormwater Facility Types and Applicability 45
Table 7. Design Storms and Precipitation Depths 46
Table 8. Prescriptive Sizing Factors 47
Table 9. Design Storms and Precipitation Depths 53
Table 10. Sand Media Specifications 70
Table C-1. Invasive and Noxious Weeds in Oregon 123
viii
LIST OF FIGURES
Figure 1. Lake Oswego Watersheds 4
Figure 2. Summary of City Review and Permitting Process 10
Figure 3. Land-Use Process 12
Figure 4. Non-Land Use Process 13
Figure 5. Public Improvement Process 14
Figure 6. Erosion and Sediment Control Process 15
Figure 7. Site Assessment Process 33
Figure 8. NRCS Soil Classification in the City of Lake Oswego 34
Figure 9. Wetlands and Areas of Historic Landslides 36
Figure 10. Setbacks from Foundations and Property Lines 40
Figure 11. Stormwater Design 51
Figure 12. Planting Requirements for Vegetated Facilities 55
Figure 13. Soil Classification 56
Figure 14. Vegetated Filter Strip 74
Figure C-1. Considerations for Plant Selection in a Stormwater Facility 125
ix
ACRONYMS
AASHTO American Association of State Highway and Transportation Officials
APWA American Public Works Association
ASTM American Society for Testing and Materials
CFR Code of Federal Regulations
cfs cubic feet per second
CIP Capital Improvement Plan
CN Curve Number
CWA Clean Water Act
DEQ Oregon Department of Environmental Quality
DMA Designated Management Agency
DO Dissolved Oxygen
DOE Washington Department of Ecology
DOGAMI Oregon Department of Geology and Mineral Industries
DSL Oregon Department of State Lands
EPA United States Environmental Protection Agency
ESC Erosion and Sediment Control
FEMA Federal Emergency Management Agency
fps feet per second
GIS Geographic Information System
GULD General Use Level Designation
HDPE High-Density Polyethylene
HSPF Hydrologic Simulation Program-Fortan
LO Lake Oswego
x
LOC Lake Oswego Code
LU Land-Use
MODRET Model for Retention Pond Design
MS4 Municipal Separate Storm Sewer System
NGVD National Geodetic Vertical Datum of 1929 (current datum used by City)
NPDES National Pollutant Discharge Elimination System
NRCS Natural Resources Conservation Service
O&M Operation and Maintenance
OAR Oregon Administrative Rule
ODFW Oregon Department of Fish and Wildlife
ODOT Oregon Department of Transportation
OISC Oregon Invasive Species Council
ORS Oregon Revised Statutes
OSBEELS Oregon State Board of Examiners for Engineering& Land Surveying
PE Professional Engineer
PFAs Per- and Polyfluoroalkyl Substances
PICP Permeable Interlocking Concrete Pavement
psi pounds per square inch
PVC Polyvinyl Chloride
Q Discharge, usually in cfs
ROW Right-of-Way
SBUH Santa Barbara Urban Hydrograph
SFR Single Family Residential
SWMM Stormwater Management Manual (Lake Oswego)
xi
TAPE Technology Assessment Protocol—Ecology(Washington state)
TMDL Total Maximum Daily Load
TSS Total Suspended Solids
UIC Underground Injection Control
UST Underground Storage Tank
VSS Volatile Suspended Solids
WQ Water-Quality
xii
1 INTRODUCTION
The Clean Water Act (CWA) of 1972 prohibits the discharge of pollutants into waters of the US and was
promulgated through amendments of the Federal Pollution Control Act (1948). It established the
requirement for water quality standards and created the basic structure of the National Pollutant
Discharge Elimination System (NPDES) program. Revisions in 1987 created the framework for regulating
stormwater discharges including those from Municipal Separate Storm Sewer Systems (MS4s).
The City of Lake Oswego (City) received its first NPDES MS4 Phase I permit(hereafter"MS4 permit")
from the Oregon Department of Environmental Quality(DEQ) in 1995 as a co-permittee of the
Clackamas County permit (#101348) which currently includes the jurisdictions of Clackamas County,
Gladstone, Happy Valley,Johnson City, Lake Oswego, Milwaukie, Oak Lodge Sanitary District, Oregon
City, Rivergrove,West Linn, and Wilsonville.
The Clackamas County MS4 permit was re-issued by DEQ in October 2021. While there are many aspects
and programs associated with the MS4 permit, this Manual fulfills the following requirements:
1. Prioritize green infrastructure and low impact development.
2. Require a site performance standard for stormwater management.
3. Require long-term maintenance of stormwater facilities.
4. Require an erosion and sediment control (ESC) program that minimizes construction site
discharges.
The requirements of the MS4 permit are implemented primarily through the Lake Oswego Municipal
Code (LOC) Chapters 38 (Utility Code -Stormwater Management) and 52 (Erosion Control).The City's
municipal code is implemented through the stormwater requirements of the City's Stormwater
Management Manual (SWMM), the Erosion Control Manual, the Engineering Design Standards, and the
Standard Detail Drawings.
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1.1 PURPOSE
The City's SWMM contains guidance and standards to implement the City's stormwater program and
mitigate the impacts of stormwater from the creation and redevelopment of impervious area. It is a
dynamic document and updated periodically to reflect the current state of stormwater practices and
treatment technologies and to address new water-quality requirements from the Oregon Department of
Environmental Quality(DEQ). It is intended for use by developers, stormwater professionals,
contractors, and others responsible for managing the stormwater created by impervious surfaces in the
city.
1.2 SWMM HISTORY
The City's SWMM was created in 2016 from the 2003 Surface Water Design Manual.The 2016 SWMM
was subsequently updated in 2020 primarily to address requirements of the City's relatively new Class V
Underground Injection Control (UIC) permit.This document, an update of the 2020 SWMM, reflects the
requirements of the MS4 permit that was re-issued in 2021 and revised Total Maximum Daily Load
(TMDL) allocations set by DEQ in 2019 and 2025. A list of the major revisions from the 2020 SWMM are
listed prior to the Table of Contents of this SWMM.
1.3 CLIMATE CHANGE
Climate change models predict hydrological changes caused by increases in global temperatures.
Previous climate models have accurately predicted changing climate patterns but did not expect the
changes to occur so rapidly.
The City is currently experiencing the more intense storms and prolonged dry periods predicted for the
future by climate models. Storms that used to provide 0.5 inches of rain in 2 to 3 days now build quickly
and discharge the same amount of precipitation in less than 24 hours and cause flooding. As these types
of storms occur more frequently,the City expects its stormwater system to become overwhelmed by
the stormwater volume created by the storms.
Paradoxically,the region's normally dry summers are becoming drier and causing it to experience
regional drought (Bumbaco, et. al, 2024) and higher summer temperatures. October 2022 was the 27th
driest and 3rd warmest since 1895. Snowpack and stream flows in the region are also affected by climate
change.The region's snowpack during the winter of 2022-2023 was the 4th highest since 1991 due to
several atmospheric rivers. However, a heat wave in May 2023 (the 3rd warmest May since 1895)
resulted in the rapid melting of the snowpack and subsequent low flows in watersheds that are
dependent on snowpack recharge during the summer.While the region was classified as abnormally dry
in the Fall of 2022, it was designated as being in a moderate to severe drought by the Fall of 2023 due to
the loss of snowpack in May 2023.
These swings in temperature and precipitation can have profound impacts on the aquatic habitat in our
rivers and streams as they experience high flows in the winter, elevated summer temperatures, and
reduced summer stream flows. Infiltrating stormwater in the winter will reduce flooding, erosion, and
hydromodification while augmenting stream flows in the summer with cooler groundwater.
-2-
Expected Climate Change Patterns
• An increase in flooding and overall rainfall intensity including a greater frequency in storm
intensity previously only seen every 25 years.
• Increased rainfall intensity and volume will cause increased hydromodification in stream,
increased stress on the public storm water system, and increased property loss due to erosion.
• No substantial change in annual rainfall is expected, however storm intensity is expected to
increase, e.g. more atmospheric rivers causing destructive streamflows and increased
flooding.
• The Pacific Northwest region is expected to experience hotter and drier summers and warmer
winters.As more precipitation falls as rain in the winter and as the snowpack disappears
before summer because of the warmer temperatures, the availability of potable drinking
water and streamflows to support aquatic species will decrease.
• As streamflows decrease, river levels are expected to decrease which may affect the ability of
hydroelectric plants to provide enough electricity for expected power grid needs in the hotter
summers.
(Adapted from Fleischman, 2023 and Dalton et. al. 2013):
1.4 STORMWATER EFFECTS
Development can affect streams by: Stormwater is the precipitation (rain and snow) that cannot
infiltrate into the soil. It is collected through a network of
• Decreasing infiltration of catch basins and inlets before being conveyed by pipes,
precipitation. culverts, ditches, and streams to the Willamette River,
• Increasing storm water volumes. Tualatin River, and Oswego Lake (See Figure 1). While the
• Decreasing shallow groundwater entire system is known as the public surface water
(interflow)mixing with streams management system,the public stormwater system is the
during the summer. network of catch basins, inlets, pipes, culverts, ditches, and
• Destabilizing stream stormwater facilities used to treat and convey stormwater to
temperatures. receiving waters.
• Decreasing reaction time of
The City collects a stormwater development charge from
streams to the onset of
precipitation. development projects connecting to the public stormwater
system. A monthly surface water fee is collected from as part
• Increasing duration of peak of the City's utility bill. These fees provide funds to:
flows in a stream from a storm.
• Increasing hydromodification
• Manage and protect natural resources
resulting in decreased stream • Repair, replace, and maintain the public stormwater system
depths and increased erosion. • Comply with DEQ's requirements for the protection of
• Increased property loss due to water quality as stipulated in the MS4 permit, UIC permit,
erosion. and TMDL Implementation Plan.
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-4-
1.4.1 Water Quantity Effects
Without treatment or detention, impervious surfaces will increase stormwater volumes and decrease
the time between the start of a storm event and the increase of flow in a stream.This can result in
flooding and erosion throughout the city.
Some areas of Lake Oswego have either no public stormwater system or an undersized system. During
periods of heavy rain, local flooding and erosion may occur as the existing drainage pattern or
stormwater system is overwhelmed by stormwater created by increased impervious areas.
Utility conflicts, lack of right-of-way(ROW), and the cost of obtaining property quickly makes many
public stormwater projects monetarily infeasible. Requiring construction projects to manage
stormwater onsite reduces local flooding, erosion, and property loss during periods of heavy rain.
1.4.2 Hydromodification Effects
Streams and other receiving waters are affected by the
timing,velocity, and volume of stormwater. As impervious
area in a watershed increases, the time between the onset
yet..
of a storm and its effect on streams decreases as infiltration
is reduced and a greater percentage of rain is converted
I. immediately to stormwater. Hydromodification occurs as
{ • streams adapt to larger flows and velocities. Streams
•
. become steeper,wider, and deeper as they experience
erosion from higher stormwater volumes and velocities.
- �' While sandy streambeds experience erosion with small
changes in stream velocity, streambeds composed of clay
Flooding in Lake Oswego soils can also experience erosion with longer durations of
peak streamflows.
Soil from streambeds and streambanks is mobilized and re-deposited downstream as stream velocities
decrease. Sediment deposits result in shallow stream depths and cause elevated stream temperatures
(Lane 1955; Leopold and Maddock 1953). Erosion and sedimentation adversely affect aquatic life and
Effects of Hydromodification
• Increased sediment in streams results in shallow stream depths.
• Shallow stream depths from sedimentation result in higher stream temperatures, decreased
stream oxygen, and adverse effects on aquatic life and habitat.
• Changes in stream channel direction or geometry results in additional flooding and erosion as
a stream adapts to new conditions.
• Properties adjacent to streams experience property and tree loss due to erosion.
-5-
habitat as vegetated streambanks and riparian trees are undercut by the increase in streamflow and
velocities. Requiring construction projects to infiltrate to the extent practicable and matching post-
development flowrates to pre-development flowrates reduces hydromodification.
1.4.3 Water Quality Effects
As streams experience elevated flows for a longer duration,their streambanks erode to accommodate
the increased flow resulting in decreased stream depths during dry periods. Stream temperatures
increase with decreased stream depth.
Groundwater can improve stream temperatures through cool inflows (50 to 60° F) to streams in the
summer. However, the ability of shallow groundwater to stabilize summer stream temperatures is
decreased as infiltration is impeded by impervious areas.
Stream temperatures higher than 65°F have a deadly
effect on aquatic life and habitat especially salmon.
• Prioritizing infiltration over detention reduces stormwater
volumes to streams in the winter, increases summer
groundwater inflows to streams, and stabilizes stream
•
;_*- .."4s3 temperatures.
Stormwater mixes with many of the materials it comes
into contact with and carries it to the nearest waterway.
Dirt, oil,feces, litter, and microscopic metal particles from
Cutthroat fry from Springbrook Creek tires and brakes mix with stormwater and can cause a
(Photo Credit: ABR,Inc) decreased water-quality when it enters a stream or other
waterway.
Stormwater that enters a traditional catch basin (no sump or water-quality snout) is not treated and is
discharged directly to streams. Stormwater from projects creating or redeveloping 1,000-sq ft or more
of impervious area must be treated through stormwater facilities before being discharged to the City's
surface water management system.
1.5 IMPAIRED RIVERS AND STREAMS
Sections 303(d) and 305(b) of the CWA requires DEQ to determine if a waterway contains pollutants at
levels that exceed water-quality standards.The current DEQ Integrated Report, commonly referred to as
the "303(d) list", was approved by EPA in September 2022.While only Oswego Lake and Oswego Creek
were specifically listed in the 2022 assessment, an impaired segment may include all of the tributaries to
the waterway(see Table 1).
DEQ uses water-quality data to evaluate the most common beneficial uses such as aquatic life, drinking
water, and recreation. Waterbodies that exceed the water-quality standards are identified as impaired.
To address impairments identified for a waterway on the 303(d) list, DEQ calculates the total maximum
daily load (TMDL) that can be assimilated by a stream or river while maintaining the most stringent
beneficial use of the impaired waterway.
-6-
Table 1. Impaired Streams in Lake Oswego.
Stream Affected Stream Reach Tributary Stream Parameter Time Period
Fanno Carter Creek to Tualatin Dieldrin1
Creek River Carter Creek TTCE1 Not Specified
Fanno Carter Creek to Tualatin Total Iron1
Creek River Carter Creek Copper Not Specified
Fanno Carter Creek to Tualatin Spawning
Creek River Carter Creek Dissolved Oxygen (Cool Water)
Spawning
Fanno 1"through 4th order Carter Creek (Cool/Cold
Creek streams Ball Creek Dissolved Oxygen Water)
Fanno 1"through 4'order Carter Creek Biocriteria,Aquatic Weeds4
Creek streams Ball Creek Chromium VI1,Zinc3 Not Specified
Lost Dog Creek
Oswego Springbrook Creek
Lake Lake Boones Ferry Algal Blooms Not Specified
Lost Dog Creek
Oswego 1"through 4'order Springbrook Creek Spawning
Creek streams Boones Ferry Temperature' Year Round
Lost Dog Creek Biocriteria
Oswego 1st through 4'order Springbrook Creek Zinc3 Spawning
Creek streams Boones Ferry Copper2•4 Year Round
Benz(a)anthracenel•4
Benzo(a)pyrene'•4
Benzo(b)fluoranthene 3,41.4
Lost Dog Creek Benzo(k)fluoranthene"4
Oswego 1"through 4'order Springbrook Creek Chrysene"4
Creek streams Boones Ferry Indeno(1,2,3-cd)pyrene"4 Not Specified
Tryon Palantine Hill Creek to Spawning
Creek Willamette River Nettle Creek Dissolved Oxygen Oct 15—May 15
Tualatin McFee Creek to Streams on City's Spawning(Cool
River Willamette River south side Dissolved Oxygen' Water)
Tualatin McFee Creek to Streams on City's Biocriteria, Harmful Algal Blooms,
River Willamette River south side Total Iron1 Not Specified
Tualatin McFee Creek to Streams on City's
River Willamette River south side Dieldrinl•3 Not Specified
Willamette Clackamas River to Streams on City's
River Johnson Creek east side Biocriteria;Cyanide';Temperature All Year(Temp)
Ethyl benzene', PAHs', PCBs1;
Willamette Clackamas River to Streams on City's Hexachlorobenzenel;Aldrinl;
River Johnson Creek east side Dieldrinl; DDE 4,41; DDT 4,41 Not Specified
-7-
DEQ determines the number and type of jurisdictions currently
Beneficial uses include: discharging to the impaired waterway and identifies them as
• Domestic water supply Designated Management Agencies (DMAs). A maximum load is
• Fishing calculated for each DMA, or group of DMAs,that can be
• Industrial water supply discharge to the waterway on a daily or seasonal basis.This is
known as a TMDL allocation.
• Boating
• Irrigation After the TMDL allocation is set, DEQ determines which land
management practices the DMA, or group of DMAs, can use to
• Water contact recreation reduce current loading. The DMAs submit a TMDL
• Livestock watering Implementation Plan (Plan)to DEQ using these management
• Aesthetic quality practices or proposing other practices to meet the TMDL
• Fish and aquatic life allocation. Once the Plan is approved by DEQ, the DMA
implements the approved practices through municipal code,
• Hydropower the SWMM, and the Engineering Design Standards.The TMDL
• Wildlife and hunting allocations are enforced through the MS4 or other NPDES
• Commercial navigation permit as a wasteload allocation or through the TMDL
(OAR 340-041-0340) program as a load allocation.
The City is a DMA for the Tualatin River and Willamette River TMDLs (see Table 2) which, together,
affect all of the watersheds in the City. The SWMM requirements help the City meet these TMDL
allocations.
Table 2. City Watersheds affected by TMDLs
TMDL Basin Watershed' Issue Date Parameter
•
2001 • Temperature (surrogate—effective shade)
• Bacteria
Tualatin River Carter Creek
Basin
Ball Creek Revised 1988 Parameters:
Lower Tualatin' 1988/2012 • pH
• Chlorophyll a(surrogate—total phosphorous)
• DO2 (surrogates—TSS2 and VSS2)
• Bacteria
Lower 2006 • Mercury
All watersheds • Temperature (surrogate—effective shade)
p ( g
River in the City 2019 Revised mercury (surrogate TSSZ)
2025 Revised temperature
1 - Lower Tualatin includes the southern area of the City. TSS=total suspended solids; VSS=total volatile suspended solids);
DO=dissolved oxygen
-8-
1.6 DOCUMENT HIERARCHY
Several documents, in addition to the SWMM, govern stormwater management in the city.The
Engineering Design Standards facilitate the planning, design, and installation of conveyance
infrastructure to serve new and future development and to upgrade existing infrastructure.The
Standard Details provide engineers with granular detail of stormwater structures for conveyance and
water quality.The ESC Manual is used to decrease construction site stormwater during development.
While these documents and the SWMM complement each other,they are rarely updated at the same
time. In the event of a conflict between their requirements, the requirement that is most protective of
water quality retains primacy.
-9-
2 DEVELOPMENT PROCESS
The City's requirements for stormwater management vary depending on the proposed project size and
type of development. Most projects start with a pre-application conference for the applicant to discuss
the proposed project, potential constraints, and requirements of the approval process with staff(see
Figure 2).
In this Chapter and those that follow it,the terms"shall"and "must" are mandatory
while the terms "should"and "may"are optional.
•
Conduct Site Assessment Design project Construct Project
a, Determine design requirements
ea
ea
0 tA.5
0.
a
Y � Engineering and Planning Staff Engineering Staff Engineering Staff Inspectors
Project Timeline
f6 • Preliminary Stormwater Report • Final Stormwater Report • Recorded O&M Plan
�^ = • Final Geotechnical Report •Stormwater Certification
E • Preliminary Geotechnical Report
•Construction Plan Set • DEQ UIC Approval
• Preliminary Site Plan • Draft O&M Plan •As-Built Drawings
Land-Use Application
Land Use Approval
1=
DSL/ODFW Permits
Building Permit
"' ESC Permit
o Utility Plan Approval
c Traffic Control Permit
Street Opening Permit
Tree Permit
p Project Stage When Activity Commonly Occurs
DEQ—Oregon Dept of Environmental Quality; DSL—Oregon Dept of State Lands;ESC—Erosion and Sediment Control;
O&M—Operations and Maintenance Plan;ODFW—Oregon Dept of Fish and Wildlife; UIC—Underground Injection Control
Figure 2. Summary of City Review and Permitting Process
- io-
2.1 PLAN REVIEW
Most single-family residential (SFR) projects are reviewed by Engineering Development Review staff. A
land-use review and conditions of approval are generally required for complex projects such as
partitions, subdivisions, and commercial projects (See Figure 3)whereas simpler projects can proceed to
plan submittal (see Figure 4).At the time of land-use application and construction plan submittal, a
stormwater report must be submitted to the Engineering Development Review staff for review and
approval.
Projects that are required to provide public improvements must apply for a public improvement permit
and submit construction plans to Engineering Development Review staff for review and approval (see
Figure 5).The City Engineer may require that the public improvement be completed before the
development of private tax lots.The decision of the City Engineer is final.
2.2 CONSTRUCTION INSPECTIONS
When the construction plan set is submitted to the Engineering Development Review staff,the applicant
must also submit an erosion control and sediment (ESC) plan to the City's ESC Inspector(see Figure 6).
After receiving the ESC permit,the applicant must install the ESCs, schedule the initial ESC inspection,
and wait for approval before starting construction. Additional information is provided in Chapter 12
(Erosion and Sediment Control).
During the construction of public stormwater infrastructure, other construction inspections must be
coordinated with the City's Construction Inspectors.
Failure to install ESCs and obtain approval of the first ESC inspection before
clearing, grubbing, or starting construction is a violation of the stormwater code
and the ESC permit. It is subject to citations,fines, and stop-work orders.
2.3 POST-CONSTRUCTION
After construction,the City requires surveyed as-builts as a post-construction submittal. Contractors for
capital improvements(CIPs) projects must provide surveyed as-builts to the City's CIP Project Manager
for review and approval. Applicants completing public improvements must provide surveyed as-builts to
the Engineering Development Review staff for review and approval. For private projects, a composite
utility plan must be submitted to the Engineering Development Review staff for review and approval.
Public improvements and CIP projects must undergo a warranty period of 1 year before City acceptance
of a facility or structure. In addition, contractors or applicants must post a 1-year maintenance bond.
Applicants constructing private stormwater facilities must provide documents as detailed in Section 4.3
(Post-Construction Submittals).
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Yes
Submit Land Use
CO Application No; require revisions Public No — ! Public
QImprovement Building Permit Improvement
Required? + Permit
MD
c c
°' Review for
Issue conditions
Stormwater Approved? of approval
c CD of
w o
c
110 (L)
c E
c (0 Manage Land Issue Land Use
co
a cu Use Case Decision
0
Figure 3. Land-Use Process(modified from OTAK,2022)
- 12-
gc Construction
cc Plans andStart Post-Construction
Q LhIESCs
o- Submittals �, Construction Submittals
• o c a) c c -o
o_ � o 2 o ,_
N '= =
Cr
r c, c,
a0 4--'
c c
Review against
v E Stormwater LandStormwater and ESC Final ESC
UseYes
Requirements ESC Plans 1st ESC Approved
o Conditions and met? approved Inspections Approved Inspections Inspection
u_iSWMM
IF
a) a)
FE
>-
I.
CC
a)
o Building Permit ESC Permit
c Issued Closed Out
m
Figure 4. Non-Land-Use Process (modified from OTAK, 2022)
- 13-
. Construction
Construction starts Submit As-
a, Plans and Construction
`—' Submittals (bond,warranty _ . Complete builts
T.Q c a requirements)
Q o ,_
� .z � -,
c v
a) a) o L_
V IIv
CC CC
C Review against U
a) Land Use Stormwater
c Conditions of Requirements —Yeses Issue Permit
bziApproval met? Approved _
w
Yes
,I,
uC City Y Warranty Final City Transfer to GIS
a Inspections Period Yeses Acceptance
and notify
E c Inspection p Public Works
a
No; extend maintenance warranty I
Figure 5. Public Improvement Process(modified from OTAK, 2022)
- 14-
Application Application Application
Complete? Yes Plan Review Approved?
No No Yes
Issue Permit Install ESCs Schedule 1st
(Accela) Inspection
1st Inspection' 2nd Unscheduled 3rd Inspection' ESC Permit
(6010) Approved? Yes Inspection2 Approved? Yes Inspections (6050) Approved? Yes Complete
(6030)
•
No No No
1—Conducted after erosion and sediment controls have been installed but before construction begins;2—Scheduled before concrete work begins(pre-footing for private projects);3—Scheduled after soil has been stabilized and stormwater facilities have been
constructed for private projects and prior to closeout for public improvements and capital improvement projects.Post-construction submittals must have been received and approved by the City's ESC Inspector.
Figure 6. Erosion and Sediment Control Process
- 15-
2.4 STORMWATER FACILITY ALTERATIONS
Alterations of a stormwater facility must be submitted to the Engineering Development Review staff for
review and approval after they have been transferred to the facility owner.Any changes must comply
with the current ESC requirements.Alterations include restorations, renovations, or replacements.They
do not include normal maintenance such as replacing media filters in a water-quality vault or removing
sediment in an infiltration gallery.
2.4.1 Restorations and Renovations
Stormwater facilities may need restoration or renovation due to
deferred maintenance. Renovations and restorations differ in the
Restoration vs Renovation
facility's condition and the type of work required to bring the
A restoration is a non- facility back to normal operating capacity.
structural repair to a failing Non-structural repairs to a failing stormwater facility, such as
stormwater facility and replacing soil in a stormwater planter or dredging a detention
requires adherence to the pond, constitutes a restoration. Stormwater facility restorations
original stormwater must adhere to the original approved plans or land-use
requirements. requirements. If a conflict exists between the approved plans
and the land-use requirements, then the requirement that is
A renovation is a structural most protective of water-quality will apply for the restoration
repair to a failing stormwater
facility OR any repair to a Renovations must adhere to the current SWMM requirements.
failed stormwater facility. It Any work on a stormwater facility that no longer provides
requires adherence to the stormwater treatment or detention is classified as a renovation.
current SWMM requirements. Major repairs on a failing or failed stormwater facility, i.e.,
replacing a perforated pipe or a chamber of an infiltration gallery
are defined as renovations.
2.4.2 Replacements
Stormwater replacements are treated as a new project and must adhere to the current SWMM
requirements.
2.4.3 Augmentation
Projects that discharge to an existing facility must adhere to the current SWMM requirements even if
the amount of impervious area does not exceed the stormwater thresholds.A stormwater report must
be submitted to the Engineering Development Review staff for review and approval.The report must
show that the existing facility has capacity for all of the impervious area currently discharging to it in
addition to the stormwater that will be discharging to it with the new impervious area.
If the existing facility cannot provide onsite retention,then the report must show that the facility meets
the requirements of Section 7.5 (Water-Quality Limited Streams) and Section 8.3 (Capacity Analysis).
- 16-
If more than 3,000 sq ft of impervious area will be discharging to the facility after construction,then the
stormwater report must show that the facility meets the Flow Control requirements in Section 7.6 (Flow
Control) and Section).
If more than 10,000 sq ft of impervious area will be discharging to the facility after construction or there
is a hydraulicly-restrictive layer 15 feet below the existing facility,then the stormwater report must
provide a groundwater mounding analysis showing that groundwater separation requirements will still
be met even if groundwater mounding occurs below the facility.
- 17-
3 STORMWATER THRESHOLDS
The following thresholds for stormwater management apply to all projects in the City.The SWMM and
other documents (see Section 1.6—Document Hierarchy) provide design requirements for stormwater
engineers working on private and public projects in the City.
3.1 PROJECT CLASS
For the purposes of determining stormwater management Projects that occur over a 3-year
requirements, projects are categorized based on the period and which exceed the
amount of impervious area created or replaced (see Table stormwater thresholds must manage
3). Projects using an existing facility must follow the stormwater for the current project
requirements of Section 2.4.3 (Stormwater Facility based on the requirements of the
Alterations—Augmentation even if the following SWMM.
thresholds are not exceeded for the project.
Example:In June 2025, a 600-sq ft
3.1.1 Impervious Area Calculation patio was built and was exempt from
The total amount of impervious area being created or the stormwater management
redeveloped must be calculated when determining the because of the 1,000-sq ft threshold.
project class.The total impervious area, as well as the In September 2027, a 750-sq ft
amount of impervious area treated by each stormwater garage was submitted for plan
facility, must be noted on the stormwater plan sheet and review. It would be subject to the
discussed in the stormwater report. stormwater requirements because
the cumulative 3-year effects of the
Pervious pavers and permeable pavement are considered projects is greater than the
to be stormwater facilities.The area covered by pervious stormwater thresholds(600 sq ft
pavers and permeable pavement must be included in the +750 sq ft>1,000 sq ft).
calculation of the total impervious area.
Pools and pool decks are considered to be impervious as well as the roof area delineated by the gutters,
eaves, and drip edges.
Stormwater management is required if a project reaches the stormwater thresholds even if a building
permit is not required for the project. Impervious examples that do not require a building permit
include, but are not limited to, sports courts, artificial turf, outdoor kitchens,flatwork, and hardscaping.
Plans for these projects must be submitted to the Engineering Development Review staff for review and
approval.
3.1.2 Small Projects
Small Projects create 1,000 square feet or more of impervious area but less than 3,000 square feet.
Small Projects which, over the period of three years, cumulatively create and/or replace 3,000 sq ft or
more of impervious area will be considered Large Projects for the purposes of project classification.
- 18-
3.1.3 Large Projects
A project is identified as a Large Project if the impervious area created and/or replaced is 3,000 sq ft or
more of impervious area.A project is also identified as a Large Project if the total amount of created
and/or replaced impervious area over three years is 3,000 sq ft or more.The primary difference
between Small and Large Projects is that Large Projects are required to provide Flow Control.
Table 3. Project Requirements based on Classification
Small Project Large Project
Creation and/or replacement of
>_1,000 sq ft but<3,000 sq ft of Creation and/or replacement of
Project Requirements impervious area ?3,000 sq ft of impervious area
Design by Licensed Professional) ✓ ✓
Onsite Stormwater Retention ✓ ✓
Water Quality Treatment' ✓ ✓
Flow Control3 ✓
Backwater Analysis' I ✓ I ✓
Downstream Analysis3 ✓
DEQ approval of UICs4 ✓ ✓
1—Not required for projects using prescriptive sizing; Licensed professional means civil engineer(PE)or a professional
hydrologist with a minimum 5 years hydrology and hydraulics experience;2—For projects with offsite discharges;3— For Large
Projects with offsite discharges;4—UlCs are underground injection controls and include infiltration trenches,infiltration
galleries,and drywell
3.1.4 Transportation Projects
Transportation projects are a special type of project and include street and road projects, pathways, and
sidewalks.The following transportation projects are subject to stormwater management:
• Projects creating and/or replacing 3,000 sq ft or more of impervious area.
• Utility work where half-street or full-street work is completed.
The following are considered to be creation or redevelopment of impervious area for transportation
projects:
• Changing from an uncompacted soil to a compacted gravel, concrete, asphalt, or similarly
impervious surface.
• Removal of pavement to the base course.
• Extending impervious areas beyond their current boundaries.The area beyond the current
boundaries is classified as new impervious area.
3.1.5 Dredge and Fill Projects
While dredge and fill projects typically do not result in an impervious surface, a permit from the
Department of State Lands(DSL) is required for all projects that include dredge and fill.The applicant
- 19-
must provide a copy of the DSL decision, requirements for the project, and the DSL permit to the
Engineering Development Review staff.
A City ESC permit must be obtained and implemented for all dredging or fill projects within 50 feet of a
waterway or in designated sensitive lands. Dependent on the type of work and affected waterway(see
Section 1.5— Impaired Rivers and Streams),the City Engineer may require additional conditions or
constraints.
3.2 PROJECT EXEMPTIONS AND VARIANCES
Projects may be exempted from specific requirements or the applicant may apply for a variance for a
requirement under limited circumstances and only with written approval of the City Engineer. Approval
must be obtained during the land-use process or prior to the submittal of construction plans,whichever
occurs first.
3.2.1 Exemptions
The following developments are exempt from the SWMM requirements:
• Projects that have entered the land-use process or that have submitted construction plans and
whose submittals have been deemed complete by the Engineering Development Review staff.These
projects must adhere to the requirements of the SWMM in effect at the time that the submittal was
deemed complete.
• Projects undertaken during an emergency, such as
•� where there is immediate danger of landslide, damage to
public or private property, or failure of a public facility.
-Nee-, The City Engineer must concur that there is an emergency
and may require retroactive compliance with this SWMM.
Bch _, a,' 4 The City Engineer's decision is final.
` ® `"`s` • Re-development in response to a natural disaster or fire
iv , when the redevelopment does not expand impervious
® - . surfaces beyond the original building's footprint.
•� Confirmation of the old footprint must be provided through photos and/or original building plans.
-0 .,,,r4s04.' �" "` � , • Utilities
a` '- `=40 `' o Maintenance, repair, or installation of utility facilities,
t '' 0" _ e.g. pipes, conduits, and vaults,that include replacing
, t D. ° ' the ground surface with in-kind material or materials
q,- "e. � t w 4i with similar impervious characteristics.
t� V,, o Utility work where only trenching is done and where
{r ��ss T - t A '� :• the new surface has the same impervious
characteristics as the original surface.
• Pavement Maintenance
o Pothole repair, crack sealing, and square cut patching.
-20-
o Pavement overlays that do not expand the area of coverage.
o Slurry seal that does not expand the area of coverage.
o Pavement maintenance that does not extend below the top of the road base.
3.2.2 Variances
An applicant may apply for a variance from a requirement of the SWMM during the land-use process or
the submittal of construction plans,whichever occurs first. When a variance is granted, conditions of
approval may be imposed on the applicant by the City Engineer to maintain the water-quality of the
receiving stream. Variance requirements and their approval criteria are found in LOC Subarticle
38.25.145.The decision of the City Engineer is final.
-21-
4 SUBMITTALS
The City requires construction plan submittals during land-use and
construction plan review for all projects that meet or exceed the Not following the
stormwater thresholds whether or not an applicant is required to obtain a City-approved
building permit. Proposed stormwater systems may change between land- construction plans
use approval and submittal of the construction plan set to the City, however is a violation of City
the plan set approved by the Engineering Development Review staff must municipal code and
be implemented during construction. If changes occur because of field subject to citations,
conditions,the applicant must notify the Engineering Development Review fines, and stop-
staff within 24 hours for review and approval of the changes.A revised work orders.
stormwater report and plan set may need to be submitted to the
Engineering Development Review staff.
4.1 PRE-CONSTRUCTION SUBMITTALS
The following plan sheets must be submitted to Engineering Development Review staff in order to
facilitate staff review and ensure a timely project start date for the applicant. Incomplete applications
will be returned to the applicant and can result in project delays.
4.1.1 Plan Submittals
Each required sheet must be a separate sheet that follows the basic requirements listed below. Final
plan sheets must be signed and stamped by the design engineer.
4.1.1.1 Basic Requirements
All plan sheets must comply with the City's GIS standards, as published on the City's website, and use
the local datum and benchmarks. In addition, all construction plan sheets must contain:
• The sheet number, site address, building permit number, LU case number(as applicable), PE
stamp/signature, and revision table in the title block.
• An engineering scale
- Horizontal Scale: 1 inch =20 ft
- Vertical Scale: 1 inch =5 ft
• Stationing must increase from left to right with a North arrow on each sheet pointing up (90°),
to the right (0°), or to the left (180°), as appropriate to provide the correct layout.
Each utility structure must be numbered with each structure retaining the same number across all
construction sheets.When existing infrastructure and proposed infrastructure are on the same plan
sheet,the existing infrastructure must be a light gray font to distinguish it from the proposed
infrastructure. Infrastructure to be removed or abandoned must be marked as such.
Profile views must be located under the plan view on each sheet. Stations in the profile view must
correspond to the location of the stations in the plan view.
-22-
All sheets must be a minimum of 22 inches x 34 inches. PDFs are encouraged for submittals but they
must be legible at the 24"x36" scale. Revisions must be highlighted in red font and encircled with a
"cloud" symbology. Revision dates must be documented in the title block.
4.1.1.2 Title Sheet
Small SFR projects must provide a title sheet containing the project address and contact information for
the applicant,the Project's ESC inspector, and the stormwater engineer.The following information is
required for all Large Projects and non-SFR projects:
• Index of sheets (if greater than 10) and date of last revision.
• Complete legend of symbols used in the construction plans.
• Vicinity map.
• Name, address, and emergency contact information of the applicant.
• Name, address, and emergency contact information for the stormwater engineer.
• Name, address, and emergency contact information for the Project ESC Inspector.
• Approval date of the stormwater report, if available.
4.1.1.3 Pre-Development Sheet
The pre-development sheet must include the following information within 50 ft of the project
boundaries:
• 2-ft contours (1-ft contours for sites containing slopes of 5%or less).
• Location of any existing or decommissioned septic systems and underground storage tanks.
• Location of existing soil contamination areas.
• Location of Federal emergency Management Agency(FEMA)-designated 100-yr floodplains,
flood management areas, and sensitive lands.
• Stormwater flow direction.
• Existing wastewater, stormwater, and water systems.
• Pre-Development impervious area.
• Pre-Development catchment areas.
• Infiltration testing locations.
• Existing easements.
In addition, the pre-development sheet must note the following information:
• Location of geologic hazards or steep slopes within 200 ft of the proposed stormwater facilities.
• Location of wells within 500 ft of the proposed stormwater facilities.
4.1.1.4 Erosion and Sediment Control Sheet
The ESC sheet must include the following information within 50 ft of the project boundaries:
• 2-ft contours (1-ft contours for sites containing slopes of 5%or less).
-23-
• Location of existing or decommissioned septic systems or underground storage tanks.
• Areas of soil contamination.
• Areas of sensitive lands,such as streams or wetlands, and the ESCs to protect them.
• Stormwater flow direction.
• Existing and proposed public stormwater facilities and structures and ESCs to be used.
• Existing and proposed private stormwater facilities and ESCs to be used.
• Primary access point(s) for construction traffic.
• Limits of clearing and limits of construction activities, if different.
• Perimeter controls that will be used to prevent sediment or construction debris from leaving the
site.
• Sediment control measures that will be used on and at toes of slopes.
• Stockpile locations.
• Location of concrete washout.
• Other proposed ESCs.
• General notes for erosion and sediment control.
• Wet weather notes if soil will be disturbed between October 1st and May 31st
4.1.1.5 Grading Sheet
The grading sheet must provide the following information within 50 feet of the project boundaries
• 2-ft contours (1-ft contours for sites containing slopes of 5%or less).
• Limits of activity and limits of construction, if different.
• Proposed areas of cut and fill.
• Location of existing wetlands, riparian areas, and floodplains.
• Location of existing roadways and drainage patterns.
• Location of existing and proposed terraces or retaining walls.
• Post-construction plan views of buildings and other structures.
• Location of existing and proposed stormwater facilities.
4.1.1.6 Composite Utility Plan Sheet
The composite utility plan (scale 1 inch = 100 ft) must provide the following information on the site:
• Plan view of proposed wastewater, water, and stormwater systems including structures such as
manholes, cleanouts, and pipes (including point of connection to public systems)within 100 ft of
the project or property line whichever is closer
• Easements for wastewater, water, and stormwater within 50 ft of the project.
• Sensitive lands (if applicable) and 100-yr floodplains within 50 ft of the project.
• Slopes>_ 15%within 200 ft of the project.
• ROW limits.
• Impervious areas including but not limited to structures, driveways, and hardscaping
-24-
4.1.1.7 Stormwater Plan Sheet
The stormwater plan sheet must provide the following within 50 ft of the project boundaries unless
otherwise indicated. Existing systems to be abandoned or removed must be noted as such.
• 2-ft contours (1-ft contours for sites with slopes 5%or less).
• A table of the impervious area treated by each stormwater facility and the total amount of
impervious area created by the project.
• Location of existing and proposed stormwater facilities and the conveyance system to the
facilities (dimensioned and scaled).
• Plan view of existing and proposed stormwater facilities and conveyance system from
stormwater facilities to the offsite discharge point(dimensioned and scaled) including outfall if
applicable. Existing stormwater facilities and structures to be removed or abandoned must be
noted as such.
• Cross-section views of existing(if retained) and proposed stormwater facilities and profile views
of existing (if retained) and proposed conveyance systems, including outfalls.
• Location of existing roadways, shoulders, berms, and drainage patterns.
• Existing wetlands, streams, FEMA-designated 100-yr floodplains, and flood management areas.
• City detail drawings when available; other detail drawings may be used if not available from the
City but are subject to changes by the City Engineer.
4.1.1.8 Landscape Sheet(see Standard Detail SD9-14)
• Plan view of proposed planting plan for vegetated stormwater facilities.
• Table of proposed plants including species, size, and number of plants.
4.1.1.9 Street Sheet
A street plan sheet is required for all public improvements and when sidewalks,walkways, pathways, or
driveways will be affected by the project.The street plan sheet must adhere to the requirements of the
Engineering Design Standards.
4.1.2 Report Submittals
Reports must be submitted to the Engineering Development Review staff for review and approval.The
reports must document existing geotechnical conditions, infiltration capacity, and support the choice of
the proposed or existing stormwater facilities.
4.1.2.1 Stormwater Report
All projects must provide a stormwater report discussing the existing conditions, infiltration rates, and
the proposed stormwater system.A basic stormwater report is required for all projects using
prescriptive sizing and it must discuss the reasons that prescriptive sizing is appropriate.
4.1.2.1.1 Projects using Models
A stormwater report must be submitted to the Engineering Development Review staff for all Small and
Large Projects at the time of the construction plan set submittal.The report shall provide:
-25-
• The project's summary objective, e.g., demolition and re-build of a building.
• Property address and tax lot number(current and historical, if appropriate).
• Existing conditions including:
o Soil classification and depth to groundwater based on borings from the geotechnical reports
and from infiltration tests.
o Infiltration test locations (figure) and table of results.
• Project requirements
o Size of project.
o SWMM requirements.
• Proposed stormwater facilities including:
o the total impervious area created by the project.
o a table with the amount of impervious area and source that is treated by each
stormwater facility.
o a technical analysis, using the facility hierarchy of Section 7.2 (Stormwater Facility
Selection—Facility Hierarchy), that shows why the proposed facilities are appropriate
for use at the site.
o a map of the catchment area and impervious area treated for each stormwater facility.
o Any constraints placed on proposed proprietary technologies by the State of
Washington's Technology Assessment Protocol—Ecology (TAPE) program.
• A summary of the feasibility of the proposed stormwater system and how it meets the SWMM
requirements.
• For projects with multiple facilities, a discussion of the cumulative peak flow and its duration at
the offsite discharge point.
• For projects required to provide Flow Control, the pre-development and post-development flow
analysis and a discussion of the peak flow and its duration, in hours, for each design event(pre-
and post-development).
• A table of the pre-and post-peak flows and durations for each design event (pre-and post-
development).
• An analysis of the proposed system on the existing downstream system including modeled
flows showing the increase on the downstream system's pipe capacity caused by the project.
• Proposed modifications to the downstream conveyance system, if applicable, and how it meets
the requirements of the SWMM.
• Stormwater plan sheet.
• Composite utility plan sheet.
Appendices to the report include the hydrologic and hydraulic flow calculations for the pre-development
and post-development scenarios (including curve number used), infiltration test results and test
locations, and a proposed Operations and Maintenance (O&M) plan.
A stormwater report template is provided in Appendix A.
-26-
4.1.2.1.2 Projects using Prescriptive Sizing
A stormwater report must be submitted to the Engineering Development Review staff at the time of the
construction plan submittal for all projects using prescriptive sizing.The report shall provide:
• The project's summary objective, e.g., demolition and re-build of a building.
• Property address and tax lot number(current and historical, if appropriate).
• Existing conditions including:
o Soil classification and depth to groundwater based on borings from the geotechnical reports
and from infiltration tests.
o Infiltration test locations (figure) and table of results.
• Proposed stormwater facilities including:
o the total impervious area created by the project.
o a table with the amount of impervious area and source that is treated by each
stormwater facility.
o a technical analysis, using the facility hierarchy of Section 7.2 (Stormwater Facility
Selection—Facility Hierarchy), that shows why the proposed facilities are appropriate
for use at the site.
o a map of the catchment area and impervious area treated for each stormwater facility.
• A summary of the feasibility of the proposed stormwater system and how it meets the SWMM
requirements.
• Proposed modifications to the downstream conveyance system, if applicable, and how it meets
the requirements of the SWMM.
• Stormwater plan sheet.
• Composite utility plan sheet.
Appendices to the report include the infiltration test results and test locations, and a proposed
Operations and Maintenance (O&M) plan.
A basic stormwater report template is provided in Appendix A.
4.1.2.2 Geotechnical Report
A geotechnical report must be submitted to the Engineering Development Review staff. It must be
signed and stamped by a civil engineer(PE)with a minimum of 5 years of geotechnical experience in
geotechnical analysis.The memo must include:
• Soil classification
o The classification must extend 5 feet below the bottom of the proposed stormwater
facility if completed from November 1st to March 30th .The classification must extend 7
feet below the bottom of the proposed facility if completed from April 1st to October
31st
o Soil mottling must be noted if encountered.
• A map or maps showing the extent and depth of
o Existing and proposed fill.
o Weak or unstable soil.
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o Contaminated soil and locations of underground storage tanks (USTs).
• Elevation and depth of any hydraulically-restrictive layers or bedrock.
• Groundwater elevation, if encountered.
• A table of the infiltration test results and a map showing the test locations.
• Signature and stamp of the civil engineer completing or overseeing the work.
When development is proposed for an area within 200 ft of steep slopes, with soil that has a high
erosion potential, or that has other unstable geologic conditions,the report must also evaluate the site's
potential instability from infiltration.The evaluation must include the following:
• Field investigation summary
• Statements regarding the exact nature and extent of the hazard
• Recommendations for site preparation and construction methods to minimize the effects of the
hazard.
• A description of any hazard areas that must not be disturbed by construction activities or post-
construction use
• Whether infiltration,flow spreaders, or other discharges onto the slope will increase instability
• A statement as to whether or not the proposed development can create conditions conducive to
landslides, subsidence, or further weaken the existing soil conditions.
4.2 STORMWATER PLAN REVISIONS
The City understands that, during construction, site conditions can result in
changes to the approved stormwater plans. Minor changes include changes Changes to
that do not affect facility type, facility design requirements, or water-quality. approved
Major changes such as moving a stormwater facility's location down- stormwater plans
gradient or more than 50ft from the original location, increasing the amount must be reviewed
and approved by the
of impervious area, changing the facility type, or changing design
City's Engineering
requirements require that the applicant provide a revised stormwater
report and stormwater site plan to the Engineering Development Review Development Review
staff for review and approval prior to implementation of the change. Failure staff.
to do so is a violation of the City's stormwater municipal code and will result
in fines, stop work orders, and/or reconstruction of the approved design.
The revised stormwater report must show the revision date on the cover page of the report. Revisions
within the report must be shown as redlines/strikeouts, however when a majority of the report changes
or the proposed stormwater facility or system changes,the report must be resubmitted as a new
application.
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4.3 POST-CONSTRUCTION SUBMITTALS
The City requires that the following documents and video of Post-construction submittals
newly installed pipe be submitted, reviewed, and approved by must be provided to the
the Engineering Development Review staff prior to approval of Engineering Development
the final ESC inspection. For example,the stormwater facility Review staff prior to scheduling
certification can only be submitted after the facility has been the final ESC inspection. Delays
constructed but does not have to wait for the project to be in providing the documents will
completed before it is submitted to the Engineering result in a delay of the
Development Review staff for review and approval. approval for the final ESC
4.3.1 Stormwater Facility Certification inspection.
In order to ensure that facilities are constructed as designed and
provide the intended treatment, including facilities designed with prescriptive sizing, the City requires
that the stormwater professional inspect and certify that the stormwater facilities have been
constructed in accordance with the design specifications and facility location in the City-approved
stormwater report.The certification must include 1) a photo-log of the construction process, e.g. photos
showing the excavation and the pipe layout and 2) documentation of the soil used in vegetated facilities.
The cover page required for the certification will be provided by the Engineering Development Review
staff when the ESC permit is issued.
Designers, even those using prescriptive sizing, must certify that storm water facilities were
built according to the City-approved design. The certification must be provided to the
Engineering Development Review staff prior to the final erosion control inspection.
4.3.2 DEQ Approval of Underground Injection Control Systems
The City allows drywells, infiltration trenches, and infiltration galleries for managing stormwater.These
facilities are considered UIC systems and are regulated by DEQ.The applicant must provide a copy of the
DEQ approval to Engineering Development Review staff for all private systems prior to approval of the
final erosion control inspection.
Sand filters, planters, and raingardens with an underground inlet are considered UlCs and must follow
the requirements of this section.
Public UlCs can only be constructed through the City's capital improvements program.They are not
allowed for public improvements required as a condition of development.
Private development cannot use UICs to fulfill public improvement requirements.
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4.3.3 Recorded Operations and Maintenance Plan
An O&M plan is required for stormwater facilities.The O&M Plan must include:
• Maintenance requirements and maintenance frequency,
• The stormwater site plan (as required by Section 4.1.1),
• The detail drawings of the stormwater facilities, and
• A copy of the DEQ approval for private UICs.
The City's ESC Inspector will provide the required cover page of the O&M Plan at the time of the ESC
permit issuance.The O&M Plan must be recorded in the County of Record for private stormwater
systems.A copy of the recordation, including the County stamp, must be received by the Engineering
Development Review staff prior to the final ESC inspection.
4.3.4 Pipe System Video
Video of new and replaced pipe for public systems must be submitted electronically to the Engineering
Development Review staff prior to approval of the final ESC Inspection. Pipe inspections and video must
comply with the Video Pipe Inspection Section in the most current version of the ODOT/APWA Standard
Specifications for Construction.
4.3.5 As-Built Drawings
Accurately surveyed as-builts are required for all public projects and all private projects with public
improvements. Specifications for the as-builts and GIS requirements can be found on the City's website.
As-builts must be submitted to the City's project manager for capital improvement projects or to the
Engineering Development Review staff for public improvements required as a condition of private
development.The as-builts must be approved by the City project manager or Engineering Development
Review staff prior to the facilities entering the warranty period.
For private systems, an accurately dimensioned and scaled composite utility plan must show the private
water,wastewater, and stormwater systems as they were constructed. Changes must be noted in red
font and the date of the changes must be provided in the revision block of the composite utility plan
sheet.The as-builts must be submitted and approved by the Engineering Development Review staff
prior to approval of the final ESC inspection.
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5 SOURCE CONTROL
Source control is an important component of stormwater management for non-SFR projects.The type of
source control depends on the type of activities that are expected to occur at the site.The following
source controls must be implemented for all non-SFR projects.
5.1.1 Outside Solid Material or Waste Storage Areas
Storage areas must be covered, bermed on three sides, and drain to the wastewater system.Waste and
recyclable materials must be in leak-proof dumpsters.
Hazardous material or waste storage areas must adhere to the same constraints as non-hazardous
waste but be separate from non-hazardous waste, placed off the ground, and clearly labeled as to the
contents.
5.1.2 Liquid Material or Waste Storage Areas
Outside liquid storage areas must be located in a covered area that is bermed on all sides and that
drains to the wastewater system.The storage areas must be able to contain 10%of the total volume of
the material stored or 110%of the largest container, whichever is greater,through a containment
system.
Stormwater must be diverted from areas used for outside storage of liquid and solid material
or waste.
Stationary fuel pumps must be located under cover and a minimum of 10 ft from the edge of the cover.
The area must drain to an oil-water separator appropriately-sized for the facility but with a minimum
capacity of 1,000 gallons.
5.1.3 Covers
Loading docks must provide a cover that extends a minimum of 3 feet either side of the loading area or
be able to accommodate a truck backing into the dock a minimum of 5 feet. When the covers are 10 ft
or higher,they must have a 5-ft overhang relative to the edges of the item they are covering.
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6 SITE ASSESSMENT
Selecting the right stormwater management technique must start early in the planning and design
process.Applicants must complete a site assessment(See Figure 7)to evaluate existing drainage
patterns, geotechnical conditions, hydrology, and setbacks as well as and any other SFR must provide
source control (see Chapter 5—Source Control).
6.1 EXISTING DRAINAGE PATTERNS
Oregon has adopted the civil law doctrine of drainage which states
that adjacent landowners shall maintain the normal course and
Oregon drainage law, which
volume of natural drainage.The downhill or downstream owner
originates from common law
shall accept water that has historically flowed onto their land from
or case law, has developed
without legislative action, and
upstream properties and which is not significantly altered as to the
it is embodied in court
amount and pattern.The downhill landowner may not obstruct the
decisions. Therefore, there are
runoff from the upper property if the uphill landowner is properly
discharging water onto their land. no Oregon Revised Statues to
cite pertaining to Oregon
For the uphill property owner, "properly discharging the water" drainage law. For more
means maintaining the location of the historical discharge point, information on this topic,
avoiding substantial increases in the velocity and volume of consult the ODOT Hydraulics
stormwater, and preserving the existing drainage pattern. Manual.
6.2 GEOTECHNICAL CONDITIONS
A cup of soil can hold millions of microorganisms that are critical to recycling soil nutrients, maintaining
soil structure, processing pollutants from runoff, and aiding plants in nutrient and water uptake.The
ability of a site to infiltrate is dependent on soil health and other factors such as soil classification,
topography, hydraulically-restrictive soil layers,the extent and depth of fill, and areas of soil
contamination.The City understands the importance of the soil-infiltration relationship and requires a
civil engineer(PE) with a minimum of 5 years of geotechnical experience to complete a report on the
geotechnical conditions (see Section 4.1.2 Report Submittals—Geotechnical Report).
6.2.1 Soil Classification
Classifying a soil includes determining the type of soil present at a site. As noted in the Clean Streams
Plan (OTAK, 2009), nearly half of the soils in Lake Oswego are classified as belonging to Natural
Resources Conservation Service (NRCS) Hydrologic Soil Group C(see Figure 8).Another 30 percent of the
soils are classified as Group D, and the remainder of the soils are categorized as Group B.
-32-
Site Assessment
SFR
No 1 Project?
1
Source Control
Required , ,, I
Project
No 4 Exceed 0421)
Thresholds?
1
No Stormwater
Mgmt Required
Contaminate. ► Yes
Soil Present?
No
Project
in Slide Area or ► es ►
Weak Soil?
No
Slopes >_15%
Within 200 ft?
No
'Infiltration Test
Required ,
V
Infiltration Test
Not Required,
Figure 7. Site Assessment Process
*Thresholds are the categories used to determine if stormwater management is required for a project.
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Soil is classified by the NRCS as follows :
• Group A soils have a high infiltration rate.They are predominately gravelly or sandy soil with
less than 10%clay. Infiltration rates are greater than 5.67 inches per hour and groundwater is
generally 40 inches or more from ground surface.
• Group B soils have a moderate infiltration rate and have between 10%to 20%clay. Infiltration
rates range between 1.42 inches and 5.67 inches per hour.The depth to groundwater is
generally 20 to 40 inches.
• Group C soils are typically fine-textured soils with 20%to 40%clay. Infiltration rates vary
between 0.14 inches per hour and 1.42 inches per hour. Depth to groundwater can vary
between 20 to 40 inches.
• Group D soils have a clay fraction of 40%or more. Infiltration rates are less than 0.14 inches per
hour and the depth to groundwater is generally less than 24 inches.They are not suitable for
infiltration facilities.
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N �Fisr __;,, J r 0 0.2 0.4 0.6 0.s 1 Mile n e r /) • Feel N
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Figure 8. NRCS Soil Classification in the City of Lake Oswego.
The NRCS maps were completed at a much larger scale and, while informative,they are not indicative of
the soil type at the project scale and cannot be used for the stormwater report or sizing of the facilities
(see warning on the NRCS website).
-34-
6.2.2 Steep Slopes
Steep slopes are defined as topographic relief that is 15%or greater.They can become unstable when
subject to stormwater discharged from impervious areas. For a project to include infiltration facilities on
a property with steep slopes (See Section 6.4.2—Constraints),the geotechnical report must show that
infiltration will not create slope instability, increase slope instability, nor create an erosion hazard.
6.2.3 Hydraulically-Restrictive Layers
Hydraulically-restrictive layers impede infiltration.The geotechnical report submitted with the
stormwater report must provide information on the elevation at which a hydraulically-restrictive layer is
encountered and the depth of the layer.
6.2.4 Soil Fill
The infiltration capacity of a soil can be affected by fill. Infiltration tests completed in areas of existing fill
can artificially inflate the soil's capacity for infiltration. Fill can also provide artificially created
preferential pathways for groundwater and for infiltrated stormwater. If a preferential channel is
created through fill or through grading from the project, it can create an Oregon Drainage Law issue
with neighboring properties.
The geotechnical report submitted with the stormwater report must provide information on existing
and proposed fill and its extent (vertically and horizontally). It must evaluate whether the existence of
fill will create preferential pathways for stormwater or groundwater towards neighboring properties and
the likelihood of the pathways to create or exacerbate existing flooding or drainage problems.
6.2.5 Contaminated Soil
Infiltration facilities cannot be located upgradient from nor over contaminated soil. A Phase II site
assessment, completed in accordance with ASTM E1903 (ASTM, 2019), must be provided to the City
with the stormwater report and evaluate the extent of the contamination (vertically and horizontally).
The report must be stamped and signed by a civil engineer(PE)with at least 5 years of geotechnical
experience.
6.3 HYDROLOGY
The City contains floodplains and areas with high groundwater tables, wetlands, and unstable soil (see
Figure 9).These areas impact the ability of a property to infiltrate stormwater.
All elevations in this section are must be based on the NGVD 29 datum.
6.3.1 Floodplains
The City contains many areas that are in a FEMA-designated 100-yr floodplain.The Lake Corporation
manages the 100-yr flood elevation of Oswego Lake through a spillway on the east side of the lake. For
stormwater facilities influenced by Oswego Lake, the design flood elevation (DFE) must be assumed to
be 100.7 ft. If the bottom of the facility is below 99.7 ft, the structure must be constructed to counteract
buoyant forces.
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t ,
171-T.
g,;\\T'"..
Jo • mbcdNe r ��
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- V•°''' lI \._ At',
Geology
` .� Fault Lines
/ �` Streams
` a? r
Nti f
•,+' Scarps
-, ill! =� . .,� I
Historic Landslides
Rd r - yL N O Urban Services Boundary
'•'` \ Watersheds
u `dm,w £ »,» .» : "'•'b Spring brook Creek
— .` Tryon Creek
L. \\N
Oswego Lake N
a,l 41110` .""'- Oswego Lake '\•
w M.=P Tualatin River
Ji1 )tT
0`° sa Willamette River
0 0250751
Isoil \1`r
.. /.
t, . \841115
a ( l
41- 3
• b tP
lijo,U�
i , 1411
s.r. na,e r ',
Figure 9.Wetlands and Areas of Historic Landslides
-36-
Stormwater designs for properties affected by the Willamette River must assume a DFE of 3.3 feet
above the base flood elevation reached during the 1996 flood as shown in LO Maps. If the bottom of a
stormwater facility is below the base flood elevation, it must be designed to counteract buoyant forces.
For areas with sensitive lands or within 50 ft of a waterway, stormwater facilities cannot be located in
the 25-yr design storm's floodplain. If located adjacent to the floodplain,the DFE must be assumed to be
3.3 feet above the 25-yr design storm's floodplain elevation. Stormwater facilities must counteract
buoyancy forces if the bottom is below the floodplain elevation.
Projects are exempt from the floodplain requirements if they are only repairing or maintaining existing
structures or existing infrastructure.
6.3.2 Groundwater
Groundwater interferes with a stormwater facility's ability to infiltrate stormwater. A separation from
groundwater is required by the City for all infiltration facilities.
6.3.2.1 Groundwater Separation
Groundwater may be encountered during the soil evaluation or infiltration testing. If encountered,the
elevation at which it was encountered must be shown on the infiltration test log and in the geotechnical
report.
Infiltration testing from April 1 to October 31st is unreliable in the City due to seasonally high
groundwater. Soil characterization must be completed to a depth that is 5 feet below the proposed
depth of the stormwater facility if completed between Nov 1'and March 30th and 7 feet beyond the
depth of the proposed stormwater facility if completed between April 1st and October 31st
If a deeper storm water facility is constructed than what was approved, the applicant must
submit revised boring logs showing that the facility meets the groundwater separation
requirements and that it has similar infiltration capabilities at the revised depth.
When determining groundwater separation for properties located in areas influenced the Oswego Lake,
the groundwater elevation must be assumed to be 97.7 ft. For properties located in areas influenced by
the Willamette River,the groundwater elevation must be assumed to be the highest base flood
elevation of the property. For properties with a sensitive lands overlay or that are within 25 ft of a
waterway,the groundwater elevation must be assumed to be the elevation of the 25-yr design storm's
floodplain,the groundwater elevation encountered during the infiltration test, or the groundwater
elevation encountered during the geotechnical investigation,whichever is shallowest.
6.3.2.2 Groundwater Collection and Disposal
Projects on sites with high groundwater present a special challenge for development.The volume of
groundwater to be discharged offsite can be difficult to determine and is highest during the winter when
stormwater volumes place the highest demands on the stormwater facilities. Because of the competing
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demands that would be placed on a stormwater facility and the difficulty in determining groundwater
volumes, structures that collect groundwater must not discharge to a stormwater facility.
Discharging groundwater to stormwater facilities is prohibited.
Sump pumps cannot be used to discharge stormwater to stormwater facilities.
6.3.3 Infiltration Tests
Infiltration tests must be conducted by, or under the supervision of, a professional hydrogeologist or
civil engineer(PE) with geotechnical experience. A signed and stamped infiltration report must be
completed by the supervising professional. A template for the infiltration test and report is available in
Appendix B.
6.3.3.1 Infiltration Test Methods
A minimum of three infiltration tests must be completed for all Large projects and one infiltration test
must be completed for all Small projects. Projects affecting only roadways, pathways, sidewalks, or
retaining walls must provide 1 infiltration test per 1,000 linear feet of impervious area or a minimum of
three infiltration tests.
The median infiltration rate of the tests must be used as the measured infiltration rate. While the
measured infiltration rate must be included in the stormwater report,the design infiltration rate must
be used in the stormwater model and design.
Infiltration tests must be completed using one of the following methods and under the constraints as
noted:
• Double ring infiltrometer(ASTM D3385).
o All projects
o Medium to fine-grained soil with no expansive (high plasticity) clay
• Large Scale PIT (Washington DOE, 2025, Volume V-5.4)
o Large Projects, Public Improvements, and Capital Improvement Projects
o Surface area of pit
— 12 to 32 sq ft for projects disturbing less than 1 acre
— 100 sq ft for projects that will disturb 1 acre or more
o Presoak at least 6 hours
• Encased Falling Head (ASTM D8152)
o All projects
o Medium to coarse-grained soil
• Open PIT(Gresham, 2025)
o Small Projects Only
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o All soil types
o Test area must be at least 4 sq ft.
o Pre-soak at least 4 hours
6.3.3.2 Infiltration Test Depth
The depth at which the test is completed must be at the proposed bottom elevation of the facility and
noted on the infiltration log.
Based on the requirements of the City's design standards (see Chapter 9—Stormwater Facility Design)
and standard details,the depths at which the infiltration tests must be conducted are:
• Filter Strips or Sheet Flow Dispersion 1 to 2 ft bgs
• Permeable Pavement, Pervious Pavers, or Swales: 2 to 3 ft bgs
• Planters, Raingardens, and Infiltration Trenches:4 to 5 ft bgs
• Infiltration Galleries: 6 to 7 ft bgs
• Drywells: 8 to 9 ft bgs
Post-construction infiltration testing (see Section 6.3.5—Post-Construction Infiltration Testing) is
required for all facilities not meeting these requirements. A revised stormwater report using the post-
construction infiltration test results must be submitted to the Engineering Development Review staff
prior to approval of the final ESC inspection.
6.3.4 Groundwater Mounding Analysis
A groundwater mounding analysis is required if the stormwater from 10,000 sq ft or more of impervious
area is infiltrated onsite or if there is a hydraulically-restrictive layer less than 15 ft below the bottom of
the stormwater facility.The analysis must show that groundwater separation requirements will be met
even if groundwater mounding occurs below the facility.
MODRET or an equivalent model must be used to complete the analysis.
6.3.5 Post-Construction Infiltration Testing
At the time of construction, at least one of the infiltration test locations must be within the construction
footprint of the stormwater facility. Otherwise, post-construction infiltration testing of the facility must
be completed.
Post-construction testing of an infiltration facility is also required when the facility type was changed
during construction,the location is more than 50 ft (10 ft for SFR projects) from the proposed location,
or when 10,000 sq ft or more of impervious area is infiltrated onsite.
6.4 SETBACKS
Certain site conditions may determine the type of stormwater facility that can be considered for a
project. Infiltration facilities cannot be located over utilities nor in areas of known fill, contaminated soil,
or areas where exposure is likely from hazardous waste or materials such as fuel or solvents.
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6.4.1 Onsite Wastewater Systems
Infiltration-based stormwater treatment is rarely compatible with existing septic systems and must meet
County-required setbacks. Infiltration facilities proposed for stormwater management must be located
downgradient from leach fields. A groundwater mounding analysis (see Section 6.3.4—Groundwater
Mounding) must be completed if the two systems are within 10 feet of each other.
Applicants may be required to connect to the public wastewater system,whether available within 200
feet of an existing line or not,to alleviate conflicts.
6.4.2 Constraints
Stormwater facilities that will provide onsite retention must meet the following horizontal setback
requirements, as measured from the outside top edge of the stormwater facility (See Figure 10):
• 500 feet from drinking water supply wells or springs (for UlCs only)
• 200 feet from contaminated soil. (See Section 6.2—Geotechnical Conditions)
• 200 feet from steep slopes (See Section 6.2—Geotechnical Conditions) or historic landslide
areas (see Figure 9)
• 20 feet from the maximum ponding depth for ponds and wetlands
• 10 feet from a building foundation
• 10 feet from septic systems or drain fields
• 10 feet from underground storage tanks
• 7.5 feet from utility trenches
• 5 feet from property lines
• 5 feet from ROW for private facilities
hI■I I---___
5 I I 10
InfiltrationZone 11111: • — L i
T _
tA„ {�
Figure 10. Setbacks from Foundations and Property Lines
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7 STORMWATER FACILITY SELECTION
The project type, project size, infiltration rate, receiving water, and setbacks will often determine the
type and location of an appropriate stormwater facility. All projects must provide onsite retention or
stormwater treatment of the water-quality storm event (see Table 4).All projects must provide
extended filtration for offsite discharges and a backwater analysis. All projects must provide specific
treatment if the receiving water is a water-quality limited stream, as designated by DEQ, (see Section 1.5
—Impaired Rivers and Streams). Non-SFR projects must provide treatment for copper and zinc prior to
offsite discharge. Flow control is required for Large Projects not discharging to an exempted waterway.
Table 4. Performance Standards
Requirement Project Type Performance Standards
Onsite All projects meeting Infiltrate the
Retention minimum infiltration rates 10-year,24-hour design storm
Projects that cannot meet Capture and treat the water-quality storm
Water Quality minimum infiltration rates (80%of the average annual runoff)
Reduce Suspended Solids by 80%(all watersheds)
Extended All projects with an offsite Reduce Phosphorous by 65% (Tualatin River basin
Filtration discharge and Oswego Lake watersheds only)
Non-SFR projects with an Reduce copper by 30%and zinc by 60% (all
Metals offsite discharge watersheds)
Do not exceed pre-development peak flows for
24-hour design storms with 2-year, 5-year, and 10-
Flow Control Large Projects year recurrence intervals
1—Precipitation depths for design storms are found in Table 7(Chapter 8 Stormwater Modeling)
7.1 PROJECT TYPE
The stormwater facilities appropriate for a project depend on the type of project being proposed by the
applicant. SFR projects can use raingardens, planters, swales, infiltration trenches/galleries, drywells,
pervious pavers, permeable pavement,vegetated filter strips,wetlands, and ponds.
Public improvements completed as a condition of development cannot use pervious pavement, pervious
pavers, vegetated filter strips, detention tanks, detention vaults, or UlCs to satisfy stormwater
requirements. Proprietary treatment systems and water quality vaults can only be used if they are pre-
approved in writing during the land-use process by the City Engineer and the Public Works Director.
Projects using proprietary technology must incorporate the constraints of the Washington DOE
TAPE program into their design and submit the constraints as part of the stormwater report.
-41-
Capital improvement and non-SFR projects can use any of the available stormwater facilities approved
for use by the SWMM.
7.2 FACILITY HIERARCHY
The stormwater professional must provide a technical feasibility analysis describing why the proposed
stormwater facilities provide the best treatment and management of stormwater created by the
project. Starting with the facilities in Tier 1 (see Table 5), applicants must provide a technical analysis
showing that the proposed stormwater facility will provide the most appropriate stormwater
management for the property. When using a Tier 2 facility,the applicant must show why onsite
retention is not technically feasible at the site.When proposing a Tier 3 facility,the applicant must show
why Tierl and Tier 2 facilities are not technically feasible.The feasibility analysis must be submitted with
the stormwater report.
The feasibility analysis must use the site assessment results of Chapter 6 (Site Assessment)to provide
documentation of the infiltration capability and feasibility of the proposed stormwater facility.
Table 5. Stormwater Facility Hierarchy
Tier Approved Stormwater Facilities
Infiltration Planter
Infiltration Raingarden
Tier 1 Pervious Paver
(Onsite Retention) Permeable Pavement
Infiltration Trench or Gallery
Drywells
Filtration Planter
Tier 2 Filtration Raingarden
(Extended Filtration)1 Swale
Water-Quality Vault (non-SFR projects only)
All other technologies approved for use in the SWMM
Tier 3 and meeting the restrictions of Chapter 6 (Site
Assessment)
1—Tier 2 Facilities must be used to treat stormwater before discharge offsite
If it is infeasible to treat stormwater created by the new or redeveloped impervious area triggering the
stormwater requirements,the applicant may apply for a variance to treat stormwater from an
equivalent amount of pre-existing untreated impervious area on the property.The required submittals
and criteria for approval of a stormwater variance are provided in the City's municipal code (LOC
38.25.145).The written approval of the City Engineer for the variance must be included with the
stormwater report.
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7.3 ONSITE RETENTION
All projects must provide onsite retention of the 10-yr 24-hr design storm when design infiltration rates
are at least 0.25 inches/hr and when the site assessment completed as part of Chapter 6(Site
Assessment) supports infiltration.
A lack of available surface area on the parcel following the placement of the desired structure(s) is
not grounds for determining that infiltration is not feasible.
A facility used to satisfy onsite retention must discharge to the public ROW or an alternative discharge
point that has been pre-approved, in writing, by the Engineering Development Review staff during the
land-use process or prior to construction plan submittal.To ensure proper maintenance and function,
onsite retention systems cannot be directly connected to the underground public stormwater system.
7.4 EXTENDED FILTRATION
Sites that cannot infiltrate the 10-yr 24-hr design storm must provide treatment
of the water-quality design storm, use extended filtration prior to discharging
All flows not stormwater offsite, and provide a backwater analysis.
retained onsite
must be treated Facilities providing extended filtration may be directly connected to the
using extended underground public stormwater system. Facilities not directly connected to the
filtration. underground public stormwater system must follow the requirements for
offsite discharges in Section 10.3 (Conveyance Design- Outfalls and Offsite
Stormwater Discharges).
7.5 WATER-QUALITY LIMITED WATERWAYS
The City is required to reduce concentrations of specific constituents, including phosphorous and
bacteria, by DEQ. Additional stormwater treatment is required for projects that discharge to waterways
that are designated as water-quality limited, have a TMDL, or which are included in the watershed of the
waterway with a TMDL.
All projects are required to reduce phosphorous and total suspended solids for the City to meet its
TMDL allocations. Projects that provide onsite retention or extended filtration (see Table 5—Section 7.2)
will have automatically satisfied the suspended solids and phosphorous reduction requirements.
7.5.1 Suspended Material
The City's MS4 permit requires that all projects must reduce suspended solids in stormwater by 80%
prior to discharge offsite. Bacterial reductions are required for all projects that discharge to the
Willamette River and Tualatin River watersheds and mercury reduction is required for all projects that
discharge to the Willamette River watershed.These requirements are satisfied for impervious areas that
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are treated using facilities approved for onsite retention and extended filtration (see Table 5—Section
7.2).
For non-SFR projects, proprietary treatments that have been approved by the Washington DOE TAPE
program and which have a General Use Level Designation (GULD) for basic treatment can be used to
satisfy these requirements as long as they adhere to the design and installation requirements specified
by the Washington DOE TAPE program and include the constraints in the stormwater report.
7.5.2 Phosphorous
The City is required by DEQ to reduce phosphorous concentrations in the Tualatin River and Oswego
Lake watersheds.All projects except those that discharge to the Tryon Creek watershed or directly to
the Willamette River are required to reduce phosphorous concentrations by 65%(as per equation in
OAR 340-041-0345(4)(e)).This requirement is satisfied for impervious areas that are treated using
facilities approved for onsite retention and extended filtration. For non-SFR projects, proprietary
treatments that have been approved by the Washington DOE TAPE program and which have a GULD-
designation for phosphorous treatment can be used to satisfy this requirement as long as they adhere to
the design and installation requirements specified by the Washington DOE TAPE program and include
the constraints in the stormwater report.
7.5.3 Copper and Zinc
Prior to discharge offsite, stormwater from non-SFR properties must be treated to reduce copper by
30%and zinc by 60%.This requirement is satisfied for impervious areas that are treated using facilities
approved for onsite retention and extended filtration.
Proprietary treatments that have been approved by the Washington DOE TAPE program and which have
a GULD-designation for metals treatment can be used to satisfy this requirement for non-SFR projects as
long as they adhere to the design and installation requirements specified by the Washington DOE TAPE
program and include the constraints in the stormwater report.
7.6 CAPITAL IMPROVEMENTS AND PUBLIC IMPROVEMENTS
Capital Improvement projects and Public Improvements must further reduce suspended solids and
phosphorous whenever technically feasible by providing a:
• Water-quality snout and a 2-ft sump for all new and replaced catch basins.
• 100%vegetative cover, a 3H:1V slope, and 2-ft(minimum) flat bottom,for all restored or
renovated ditches.
• Culvert orientations that match the stream orientation for all replaced culverts.
7.7 SUMMARY
Table 6 provides a list of the stormwater facilities and their applicability to the setbacks, infiltration
rates, project type, and stormwater facility hierarchy required by the SWMM.
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Table 6.Approved Stormwater Facility Types and Applicability
m
c +, o
CU E +IAc Y +' m
' (^ a) u - C N U +^7
a c v c v it c C 4- ^
c �' ° E c a a) c o
o H CD a) N •N c 'a OA 2 ft v LA ro
.1. ++ 0 0 •, rn o 72 473 GC a) J a)
ate+ LL 8- o. iv'
C C N a) J N
ce 0 0' a) _ •o a 3 +� 3 +. +.
a) U L f6 U i •i ea an E T. E •U a) r„
+' a) C +_. d U _ i U
a) C 0 ra ++ as . GC a) C •C :F •C— '^ o i
Facility Type i 0 w cf° a n a 0 o 2 E 2 ccc . v,
Drywell 1 • •' • 0.25 5 >_5 >_10
Infiltration trench or gallery 1 • •° • 0.25 5 >_5 >_10
(Permeable pavement 1 • • • • 0.25 3 >_5 >_10
Pervious pavers 1 • • • • 0.25 3 >_5 >_10
Planter,infiltration 1 • • • • • • 0.25 3 >_5 >_10
Raingarden,infiltration 1 • • • • • • 0.25 3 >_5 >_10
(Swale, infiltration 1 • • • • • I • 0.25 3 >_5 >_10
Planter,filtration 2 • • • • • • • • NA NA >_5 NA
Raingarden,filtration 2 • • • • • • • • NA NA >_5 NA
Swale,filtration 2 • • • • • • • NA NA >_5 >_10
Detention pond 3 • • • • NA NA >_20 >_20
Detention tanks&vaults' 3 • • NA NA NA NA
Infiltration pond 3 • • • • • • 0.25 5 >_20 >_20
Proprietary treatment 6 3 • • • •6 •' —' —7 —7 —7
Retention pond 3 • • • • • • NA NA >_20 >_20
Sand filter 3 • •6 •6 0.25 5 >_5 >_10
Vegetated Filter strip 3 • • • • 0.25 3 >_5 >_10
Water Quality Vault6 3 • • 1 • • I I I NA NA
Wetland, Constructed 3 • • • • • NA NA >_5 >_10
1—Does not include middle housing projects on property zoned as low density residential;2—Restrictive layers include
bedrock,expansive clays,or groundwater;3—Measured from outside edge of facility;4—Needs approval of UIC permit
manager; 5—Engineering Design Standards contains requirements; 6—Needs prior approval from City Engineer and Public
Works Director;7—Dependent on the Washington TAPE GULD requirements;NA=not applicable;SFR=Single Family Residential
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8 STORMWATER MODELING
Modeling is used by stormwater professionals to determine the required facility size and to show,for
projects required to provide Flow Control, that the post-development discharge will not exceed the pre-
development discharge.
Stormwater facility design must be completed by a civil engineer(PE) or a professional hydrologist with
a minimum of 5 years of hydrologic and hydraulic experience. Facilities sized with prescriptive sizing
factors do not require a licensed professional but must show the calculation on the stormwater plan
sheet and in a basic stormwater report. Revised stormwater reports using other approved models are
required if deviations from the prescriptive sizing requirements occur during construction.The design
storms used in modeling a project are listed in the table below.
Table 7. Design Storms and Precipitation Depths
Design Storm (24-hr Recurrence Interval) Precipitation Depth', inches
Water-Quality 1.2
2-year 2.1
5-year 2.8
10-year 3.3
1—Precipitation depths based on data from Portland HYDRA network's rain gage at PCC-Sylvania station(1976-2019)
8.1 APPROVED MODELS
The City allows models that use continuous simulation or single event models using the Santa Barbara
Urban Hydrograph (SBUH). Some software can simulate the effect of a storm event using either a single-
event or continuous simulation. Models using hydrologic soil types, rather than infiltration rates, are not
allowed.
Prescriptive sizing, a simple equation using a conservative sizing factor, can be used for Small SFR
Projects that are not using an engineering firm for the other parts of their project. It was created to help
homeowners and small contractors provide stormwater facilities for relatively simple projects such as a
sport court.
Non-SFR and public stormwater facility design must use a single-event or continuous simulation
model for stormwater design.
8.1.1 Single-Event Models Santa Barbara Urban Hydrograph
Single-event stormwater models based on the Santa Barbara Urban Hydrograph (SBUH) method are
allowed for modeling proposed stormwater systems. Single-event models using SBUH estimate a flow
hydrograph for a single 24-hr storm event using the precipitation depth, amount of impervious and
pervious areas, and a curve number that represents a land-use.Applicable to urban areas, it calculates
the stormwater volume and creates a hydrograph showing peak flows and their duration (Debo and
-46-
Reese 2003). It assumes that the system that it is modeling has full capacity. An example of a single-
event model is HydroCAD.
A Type 1-A 24-hr rainfall distribution is required when using a single-event
model. The City of Portland's
PAC is not allowed for
The Presumptive Approach Calculator(PAC) cannot be used for designing designing stormwater
stormwater facilities in in the City because of differences between the facilities in the City of
design storms, assumptions, and requirements in the stormwater manuals Lake Oswego.
of the City of Lake Oswego and the City of Portland.
8.1.2 Continuous Simulation Models
Continuous simulation models based on the HSPF method are allowed for the design of stormwater
systems. More complex than the single-event method,the continuous-simulation method models
precipitation from multi-day or back-to-back storms which are more typical of storm events in the
Pacific Northwest. Stormwater peak flows and peak flow durations are more accurately predicted
because information from surface runoff, shallow interflow, and infiltration are integrated into the
models. Continuous simulation models take into consideration that a recent storm event may still be
impacting the stormwater system and that the system does not have its full capacity available for the
storm event. Examples of continuous models include EPA-SWMM, HEC-HMS, and others.
8.1.3 Prescriptive Sizing
Prescriptive sizing may be used for rain gardens or stormwater planters on Small SFR Projects with
design infiltration rates that are less than 0.5 inches/hour.The prescriptive sizing calculation must be
shown on the stormwater plan sheet and must be included in a basic stormwater report submitted to
the Engineering Development Review staff for review and approval.
Multiplying the sizing factor by the amount of impervious area to be treated results in the required
surface area of the facility(see Table 8).A total of 3,000 sq ft of impervious area on a SFR property can
be sized using this method.
Table 8.Prescriptive Sizing Factors
Design Infiltration Rate Raingarden Planter
0.00 in/hr to <0.25 in/hrl 9% 6%
0.25 in/hr to <0.50 in/hr2 8% 5%
1—Flow-through(filtration)facilities;2—Infiltration facilities
Stormwater planters and raingardens designed with prescriptive sizing must adhere to the following
design specifications during construction:
• Ponding depth of 1 foot plus a 3-inch freeboard
• Soil depth of 1.5 ft
• Storage course of 1 ft plus a 3-inch choker course between the storage course and the soil
media
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Raingardens must be constructed with a 3H:1V side slope or flatter and a 2-ft minimum bottom width
and length. Planters must have a minimum interior width of 3 ft.
In addition, prescriptively-sized facilities must adhere to the following requirements:
• An orifice diameter of 0.5 inches is required for filtration facilities
• An underdrain is required for flow-through (filtration)facilities
• An open bottom must be constructed for infiltration facilities
A revised stormwater report must be submitted to the Engineering Development Review staff for
review and approval if the constructed stormwater facilities do not comply with the prescriptive
sizing specifications. The report must use a continuous or single-event model to show that the
facility, as constructed,meets the SWMM requirements.
8.2 MODEL PARAMETERS
Model parameters include the amount of impervious and pervious areas, curve numbers, and infiltration
rates.The total impervious area used for the model must equal the impervious area in the stormwater
report and on the construction plan set.
The basins used in the pre-development model must provide a true representation of the stormwater
flow path. Basins used for the post-development scenario must replicate the proposed stormwater
system.
8.2.1 Curve Numbers
Curve numbers(CNs) represent the land cover and infiltration capacity present at the site. When
modeling the pre-development scenario,the stormwater professional must use a curve number of 70
for the site. For impervious areas,the CN is 98.
Weighted curve numbers are not allowed due to their significant under-estimation of stormwater
volumes (Cahill, 2012). Curve numbers and time of concentrations must be provided in the narrative of
the stormwater report.
A curve number of 70 must be used when calculating pre-development flow rates.
8.2.2 Time of Concentration
Time of concentration is the time it takes for runoff to reach the point of discharge from the most
hydraulically-distant point in the basin of interest. It is affected by the slope, land use, and length. It is
composed of sheetflow, shallow concentrated flow, and channel flow. Equations to calculate the time of
concentration are available in many basic hydrology manuals.The TR20 or TR55 equations can be used
to estimate time of concentration when using the SBUH method.
-48-
The time of concentration used in the pre-development model must be a true representation of the site;
for example, a 100-ft flow path on a flat site is approximately 9 minutes.
8.2.3 Infiltration rates
The measured infiltration rate must have a correction factor of 0.5 applied to it to obtain the design
infiltration rate.The infiltration rate used in the model must be the design infiltration rate.The
maximum design infiltration rate is 10 inches/hour.
Design Infiltration Rate' = Median Measured Infiltration Rate X 0.5
1—Maximum is 10 inches/hour
For flow-through facilities,the measured infiltration rate is the infiltration rate of the soil media.The soil
used must be documented in the stormwater report.A revised stormwater report must be submitted to
the Engineering Development Review staff for review and approval if the infiltration rate of the facility's
soil differs from the design infiltration rate by>_10% .
8.2.4 Orifices
Flow control is achieved using an orifice sized to match the pre-development flowrates.The City allows a
minimum orifice diameter of 0.5 inches for vegetated facilities and 1 inch for other facilities. Orifices less
than 3 inches must be made of stainless steel, HDPE, or PVC.The orifice diameter must be greater than
or equal to the thickness of the orifice plate.
8.3 FLOW CONTROL
All Large Projects must provide Flow Control unless they can provide onsite retention of the 10-yr 24-hr
storm event. Flow Control requirements are met when the post-development flowrates are less than or
equal to the pre-development flowrates for the 2, 5, and 10-yr 24-hour design storm events.
Detention tanks and vaults cannot be used for flow control on SFR projects, middle housing projects, nor
to fulfill public improvements required as a condition of private development.
8.3.1 Exemptions
Flow Control is not required if the project can provide onsite retention of the 10-yr 24-hr storm event or
if stormwater will be discharged to an exempted water. An exemption from the Flow Control
requirement is pre-approved if all of the following conditions are met:
• Discharge is to the Tualatin River, Willamette River, or Oswego Lake,
• Discharge does not divert water that would normally go to wetlands,
• Discharge flows only through underground conveyance structures (pipes, catch basins, or
manholes)which extend to the high-water mark of the Tualatin River, Willamette River, or
Oswego Lake,
• The capacity of the downstream public stormwater system plus the Project's offsite discharge is
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sufficient to receive the discharge (maximum capacity of 80%), and
• Stormwater has been treated to the extent required (Section 7.5—Water-Quality Limited
Waterways).
8.3.2 Flow Control Procedure
Small and Large projects must provide onsite retention to the extent possible or treat the water-quality
24-hr storm event (see Figure 11).All projects with an offsite discharge are required to provide
extended filtration, a backwater analysis, and reduce concentrations of pollutants to water-quality
limited waterways (see Section 7.5—Water-Quality Limited Waterways).
Large projects must provide Flow Control unless they discharge directly to an exempted water through
an underground stormwater system (manholes, pipes, catch basins, and inlets) and the offsite discharge
will not cause the downstream public stormwater system to exceed 80%capacity. If the offsite
discharge will cause the downstream stormwater system capacity to be>_80%then a downstream
analysis must be completed.
Large projects not discharging to an exempt waterway must compare post-development peak flowrates
from the 2,5, and 10-yr 24-hr design storms with their respective pre-development flowrates as follows:
A. If the post-development peak flowrates are less than or equal to the pre-development peak
flowrates,then the design can proceed to the backwater analysis.
B. If the post-development peak flowrates are more than the pre-development peak flowrates,
then the stormwater facility must be sized to treat the 10-yr 24-hr design storm and include
extended filtration.The pre-development flowrates from the new design must be compared
with their respective post-development flowrates. If the post-development peak flowrates are
less than or equal to 110%of their respective pre-development flowrates then the design can
proceed to the backwater analysis.
C. If the post-development flowrates are more than 110% of their respective pre-development
flowrates then the stormwater facility must be sized to treat the 25-yr design storm and provide
extended filtration.The pre-development flowrates from the new design must be compared
with their respective post-development flowrates. If the post-development peak flowrates plus
the flowrates in the existing downstream stormwater system are<_80%of the capacity of the
existing stormwater system then the design can proceed to the backwater analysis.
D. If the post-development peak flowrates plus the flowrates of the existing downstream
stormwater system exceed 80%of the capacity of the existing downstream system then a public
improvement is required.The capacity analysis must follow the steps in Section 8.4 (Stormwater
Modeling-Capacity Analyses).
A public improvement is required to expand the public downstream system if flow control cannot be
achieved after treating the 25-yr storm, if offsite flows cause the public downstream system to exceed
80%capacity, or if backwater occurs offsite with the proposed stormwater design.The public
improvement must extend to a point at which these conditions are no longer present or until the public
system discharges to a waterway.
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4620
nfiltration Test No WQ Storm With Smal (NO Exempted
'equired? Extended Filtration Project? aterway?
No
See Note 1 Y@S
CYes Treat Offsite' ost<—Pre.
Discharge
No
Design
Infiltration>_ 10-Yr Storm With
0.25/Hr? Extended Filtration
See Note 2
Yes 400 Post<—
T (Pre+ 10%)?
Infiltrate 10-
Yr Storm No
25-Yr Storm With
Extended Filtration
See Note 3
Post+
Existing
<—80%7
- No
Design Completek No Backwater? t See Note 4
Downstream
Capacity
Yes Analysis
V
Stormwater
Improvement
Required
Figure 11. Stormwater Design
Notes: 1—Offsite discharges to water-quality limited streams must be treated to reduce pollutants to the extent required in Section 7.5.
2—Post-Development Flowrate cannot add more than 10%additional flow to the Pre-Development Flowrate for each design storm event.
3—Post-Development Flowrate+existing flow in public stormwater system cannot exceed 80%of the downstream capacity for each design storm event.
4—Downstream capacity required if public stormwater system downstream of project exceeds 80%(see Section 8.4)
Existing=Pre-development flow in existing public system;Post=Post-development off-site discharge;Pre=Pre-development off-site discharge;WQ=Water-Quality
-51-
8.4 CAPACITY ANALYSES
A capacity analysis is required for all projects with an offsite discharge.An upstream analysis is required
for all projects. A downstream capacity analysis must be completed for Large Projects where the pre-
development flowrates cannot be met and for Large Projects that are discharging to an exempt water
through the public stormwater system. Upstream and downstream analyses must use the following
parameters to determine the capacity of the public system:
• Built-out conditions using the City's most recent Comprehensive Plan or current zoning,
whichever contains the greater amount of lot coverage.
• Middle housing densities for properties where middle housing is allowed.
• Type 1A rainfall distribution for single-event models.
• Design infiltration rate determined during the site assessment phase of the project.
• Offsite infiltration rates using the following hierarchy:
1. Infiltration results listed in existing geotechnical reports.
2. Soil types determined by existing geotechnical reports.
3. Median infiltration rate of soil types as determined by the NRCS.
The use of weighted curve numbers in a capacity analysis is prohibited.
8.4.1 Downstream Analysis
Large projects that cannot meet flow control requirements or that discharge to an exempted waterway
must provide a downstream capacity analysis comparing the pre-development flows in the public
stormwater system with the post-development flows.
If the offsite discharges cause the downstream system to exceed 80%of its capacity, then the applicant
is required to increase the capacity of the public stormwater system so that it reverts back to the pre-
development capacity percentage. If the capacity of the existing stormwater system already exceeds
80%then the applicant must increase the capacity of the public system such that the public system's
post-development capacity is 80%or less.
Large projects that discharge to an exempt waterway must ensure that the downstream stormwater
system has sufficient capacity to manage the additional flow created by the project. If the capacity of
the post-development public stormwater system exceeds 80%then the applicant must increase the
capacity of the public stormwater system such that it reverts back to the pre-development capacity
percentage. If the downstream system is already at 80%or greater capacity,then the applicant must
provide Flow Control (Section 8.3).
-52-
Example Scenarios
Discharge To Non-Exempt Waterways Exempt Waterways
•
Existing Capacity
of Public System 65% 70% 85% 65% 70% 85%
•
Offsite Discharge+
Existing Capacity of Public
System 78% 87% 100% 78% 87% 100%
No No Flow Flow
Post-Development Improvement Control Control
Capacity of Public System Required 5 70% 5 80% Required 70% Required
The downstream analysis must be completed for each of the 24-hr design storms in Table 9 and
continue to the receiving water.
Table 9. Design Storms for Downstream Analyses
_Recurrence Interval Precipitation, inches
_25-yr 3.84
50-yr 4.27
100-yr 4.68
8.4.2 Backwater Analysis
As a final step for all projects with an offsite discharge, the applicant must document that stormwater
volumes from the project will not: 1) encroach upon or discharge onto adjacent properties except at the
approved discharge point and 2) cause or exacerbate groundwater seepage onto adjacent properties
due to backwater elevations. The storm event to be used for the analysis is the event required to be
treated for the project.
If backwater occurs, the stormwater design professional must redesign the system or contact the City
Engineer to determine what is required for a public stormwater improvement.
-53-
9 STORMWATER FACILITY DESIGN
The design and construction of stormwater facilities must follow specific standards to achieve the water-
quality requirements of the City's MS4 permit, UIC permit, and TMDL allocations.The standards can be
grouped into those that are generally the same for a facility type (see Section 9.1—General design
standards) and those that are specific to a facility(see Section 9.2—Specific design standards). Both
types of standards must be incorporated into the stormwater design. If a conflict occurs between the
general and specific design standards,the requirement that is most protective of water quality applies
to the design.
The City's standard details must be used when the construction plans Failure to provide the
are submitted to the Engineering Development Review staff for review City's standard details,
and approval.A non-City detail may be used if one is not available from when available, will
the City, however the submitted detail is subject to changes by the City result in an incomplete
Engineer.The decision of the City Engineer is final. design submittal.
9.1 GENERAL DESIGN STANDARDS
Most of the approved stormwater facilities can be grouped into types such as vegetated facilities, UlCs,
regional facilities, and proprietary treatment. Each facility type has a set of design requirements that are
the same regardless of the specific facility within the facility type.
9.1.1 Vegetated Facilities
Vegetated facilities include raingardens, planters, swales, and vegetated filter strips.All of these
facilities can be used to meet the landscaping requirements of development (see LOC Subarticle
50.06.004).
9.1.1.1 Vegetation
Vegetation must provide 100%coverage at plant maturity and include at
Plants in a facility must least 3 plant families to avoid catastrophic die-off within the facility.
represent at least3 Perennial forbs may be used for 10%of the plant palette to assist with
plant families. It is not aesthetics. Shrubs and small trees may be used to provide up to 50%of
appropriate to plant the facility coverage as long as the soil depth is increased to two feet.
three types of caryx Turf grass is prohibited from use in vegetated facilities. Appendix C
however the criteria is provides additional information on plant selection.
met when planting a Plants must be chosen from the approved plant list(see Appendix C), be
combination of caryx, in potted containers (minimum 1-gallon) or be ball and burlapped, and
deschampia, and juncus. be installed with the root crown level with the ground surface. Root-
bound plants are prohibited.
Plants must have a staggered spacing to maximize flow dispersal and increase plant viability (see Figure
12).
-54-
STORMWATER FACILITY STORMWATER FACILITY
EDGE EDGE
ON CENTER ._
SPACING
\
1 1 1 1 \ 7)ç_ N\\\
VS
111V
1
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'G 1 1 I 1 1 I
Z 1' 1 1 1 1 1 1
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In
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.n • - 1 1 1 1 1 I I
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I i A A , I
•
1 IIIIIIIIIIIII 1
VII 111111111111111 1 11 11 1111111 0 V 0
STREET
IIIIIIIIIIIII INLET
STAGGERED SPACING
Plan View
ROOT CROWN LEVEL WITH OR JUST ABOVE FINISH
GRADE.NO MULCH OR COMPOST TO BE APPLIED.
y
TAMP SOIL TO ELIMINATE AIR POCKETS IN
PLANTING HOLE.
1/
\\ \AJ.Ai%`J\i%`J\JJ\JJ\i%J�===----------J`S\•%`S`•%`J`•%`J`•%`J`J`J`V`J`�\✓\v PLANT ROOTS TO BE STRAIGHT AND UNDAMAGED
\�`�?i`3`.i?i`.i`.i`.i`.i`.i`ib' = r%,�`,.,;`,T,;Y'!`,;�;:'-. DURING INSTALLATION.
v.
`JJ`VJ`V:__ J`JJ`JJ
v.J✓✓Y
CONTAINER PLANTING
Profile View
Figure 12. Planting requirements for vegetated facilities
-55-
Bare-root trees and plants must be planted in the spring and fall (October 1 to December 1 or February
1 to April 1). Potted plants must be installed between October 15 and April 30. Plants may be installed
from May to September but must have temporary irrigation installed to ensure plant viability. Public
stormwater facilities constructed as part of a public improvement or capital improvement project must
provide permanent irrigation.
9.1.1.2 Soil
Soil used in stormwater facilities may have up
too to 20%clay. It must be classified as a sandy
90 / ^� loam, loam, or silt loam (See Figure 13); and
ryo contain a 10% biochar additive. Biochar
80 suppliers can be found at
/4
70 o \ www.pnwbiochar.org.
clay
�
Q��� 60 . Soil depths for planters, raingardens, and
swales can range from 18 inches to 24 inches.
50 silty
sandy clay A 6-inch layer of soil media must be tilled
/ 40 clay into vegetated filter strips prior to planting.
silty o
clay loam ''
30 sandy clay loam Shredded mulch, up to a depth of 2" may be
20 used to increase plant viability in the summer
silt loam �o but cannot decrease the ponding depth. If
10 sandy loam mulch is used, a 3-inch area around the
loamy silt o
sand sand ^� overflow must be rocked to prevent mulch
'oo Oo �0 'o 0 so po �o ao 'o from entering the overflow pipe. Bark
nuggets and non-shredded mulch is
Figure 13. Soil classification prohibited in vegetated facilities because of
From:Soil Health—Soil Texture and Structure,NRCS Factsheet at
nrcs.usda.gov their propensity to be transported into the
overflow pipe during storm events.
To protect plants from heat-island effects, the use of a top layer of rock in
vegetated facilities is prohibited.
9.1.1.3 Inlets
Inlets for vegetated facilities adjacent to driveways,flatwork, or streets must comply with Standard
Detail SD9-02—Curb Inlet).All inlets must be at an elevation that is above the facility's overflow
elevation to prevent backwater from occurring.
Waterproof connections are required for inlets that are cored through the side of a facility. Pipe boots
are required for lined facilities.
All vegetated facilities must provide energy dissipation at the inlet. For raingardens, planters, and
swales,the energy dissipation must be clean rock (1-Y2" to %") or a concrete pad with 1-inch tall edging.
Vegetated filter strips must use either a ift x 0.5ft rock strip or a non-galvanized 6-inch wide trench
-56-
drain that extends to the edges of the facility to evenly disperse flow.Trench drain grates must have a
load designation following AASHTO M306 standards.A load class B is required for residential driveways
and landscapes, C for commercial applications, D (H20) for industrial applications, and E (HS25)for areas
subject to loads up to 50,000 pounds or 620 psi. Galvanized trench drains are not allowed because of
durability and water-quality concerns.
9.1.1.4 Storage Courses
A storage course may be used for raingardens, swales,and planters. It can range in depth from 12 inches
to 24 inches but must be comprised of clean rock (1-%2"to%")that complies with the Subsurface Drain
Section in the most current version of the ODOT/APWA Standard Specifications for Construction.
A 3-inch choker course must separate the soil layer from the storage course. It must be comprised of
clean rock(3 "to 1/2")that complies with the Subsurface Drain Section in the most current version of the
ODOT/APWA Standard Specifications for Construction.
9.1.1.5 Underdrains
Underdrains are required for filtration facilities and must consist of a perforated pipe that extends a
maximum 2/3 of the length from the overflow to the first inlet(see Standard Detail Drawing SD9-11). If
the overflow is located in the center of the facility,the pipe must not extend longer than 1/3 of the
length on either side. For multiple-celled facilities,the underdrain must be installed only in the last cell.
A minimum 4-inch diameter perforated pipe must be used for private facilities and a minimum 6-inch
diameter pipe must be used for public facilities (See Standard Detail SD9-11)
When used, all pipe connections exiting through a vegetated facility must be waterproof.
9.1.1.6 Liners
•t" + A 30-mil PVC or HDPE liner must be installed in filtration
' r facilities and extend to a height equal to the ponding
1
• - _ depth.A HDPE liner with equivalent or better
-
specifications may be used to replace a PVC liner. Spray-
..<< ,_
P% on liners are prohibited from use in stormwater facilities.
In planters, the liner must cover the bottom and the
i ' ' sides. It must be attached using a non-rusting aluminum
flat bar(2"x 1/8") and caulk must be used to prevent
` ► water from infiltrating behind the bar. In filtration
- raingardens, the liner must extend past the top of the
4.00-
,.. facility and be staked into a 1 ft wide dirt shelf at the top
„�,,. „�,� .. � of the facility.A 1-ft deep layer of dirt must be placed on
.igg top of a raingarden liner to help secure it in place.
Spray-on liners are prohibited from use
in stormwater facilities.
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9.1.1.7 Outlets
The outlet from a swale, planter, or raingarden must be a beehive structure (see Standard Details SD8-
01 and SD8-02) that is located as far as possible from the inlets.The overflow elevation must be below
the elevation of the lowest inlet. For multiple-celled facilities,the overflow must be located in the
lowest cell. In vegetated filter strips,the outlet can be a non-galvanized non-plastic trench drain that
discharges to an approved point of discharge.
9.1.1.8 Construction of Vegetated Facilities
The following notes are required with the construction plan submittal and must be followed during
construction:
• Construction fence must protect the facility footprint plus a 10-ft buffer around it.
• Stormwater must be diverted away from the facility footprint during construction.
• Prior to constructing the facility,the native soil must be scarified to a depth of 6 inches.
9.1.2 Underground Injection Controls
UlCs approved for use in the City include infiltration trenches, infiltration galleries, and drywells. All UlCs
receiving runoff from surfaces other than roofs are required to obtain DEQ approval of the system and
provide a copy of the approval to the City with the post-construction documents(see Section 4.3—Post-
Construction Submittals). UICs receiving stormwater only from SFR roofs are not required to obtain DEQ
approval.
UICs may not be used to satisfy public improvement requirements. CIP projects may incorporate UICs
only if no other stormwater facility is feasible.A feasibility analysis must be completed and provided in
the stormwater report.The UIC permit manager must agree to the construction of the UIC.
Facilities that discharge underground, without first allowing infiltration from the ground
surface, are considered to be UICs even if the facility not normally considered a UIC.
9.1.2.1 Pretreatment
Pretreatment is required by DEQ prior to discharging stormwater to a UIC. Pre-approved treatment
includes the use of vegetated facilities or sumped catch basins with a water-quality snout. If using a
catch basin for pretreatment, the minimum sump is 18 inches for SFR projects and 36 inches for non-SFR
projects.The water-quality snout must be attached to the outlet pipe.
To allow for adequate maintenance,the maximum depth of a catch basin used for pretreatment is 3 ft
for SFR projects and 5 ft for non-SFR projects. Cleanouts,vertical standpipes, and PVC pipes cannot be
used for pretreatment. Catch basin grates larger than 2.5ft cannot be used for SFR projects because of
the weight of the grate.
Catch basins used for pretreatment of UICs but placed in landscaping must have a solid top to protect
water-quality and reduce the volume of mulch and yard debris entering the system.
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9.1.2.2 Maintenance Access
Maintenance access is required for all UlCs. Drywells must be with the drywell cover located at-grade to
provide maintenance access. Infiltration trenches must include a minimum 6-inch diameter inspection
port while infiltration galleries must provide a minimum 10-inch diameter inspection port.
9.1.2.3 Construction of UlCs
The following notes are required with the construction plan submittal and must be followed during
construction:
• Construction fence must protect the facility footprint plus a 10-ft buffer around it.
• Stormwater must be diverted away from the facility footprint during construction.
• Prior to constructing the facility,the native soil shall be scarified to a depth of 6 inches.
9.1.3 Regional Facilities
Ponds and wetlands have traditionally been used to serve more than one property with maintenance
responsibility delegated to a Homeowners Association or Neighborhood Association. Other types of
shared facilities are not allowed due to the complexities of shared maintenance among unaligned
homeowners.
9.1.3.1 Existing Facilities
Existing regional facilities can be used to fulfill flow control requirements for a project if stormwater
modeling shows that the existing facility has capacity for the proposed stormwater volume and all other
stormwater currently being discharged to it. New projects must still comply with the onsite retention
and water-quality treatment requirements of the SWMM.
When using an existing regional facility,the applicant must provide a copy of a recorded O&M Plan as
part of the post-construction submittals. It must include all property owners discharging to the regional
facility as the responsible parties and their signatures.
9.1.3.2 Vegetation
A minimum of nine plant species are required for the treatment area.The facilities must be designed so
that they do not require mowing.
Use woody vegetation to provide shade over standing water and to provide structural diversity
surrounding the pond. Maintain a 20-foot minimum distance between hydrophilic trees and shrubs
(e.g., Oregon ash, alder, willows, and dogwoods) and inlets or outlets to prevent roots from blocking
structures or obstructing maintenance efforts.Trees and shrubs cannot be planted on berms that are
four feet or taller.Trees and shrubs with a fibrous root system (no tap roots) can be planted on berms
shorter than 4 feet.A fibrous root system reduces chances of blowdown, piping, and the creation of
preferential flow paths.
Trees and shrubs must be planted on the south and west sides of the facilities when feasible to lower
water temperatures.
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9.1.3.3 Spillways
All ponds and constructed wetlands must provide an emergency overflow route (spillway)that will
convey the 100-yr storm event over the facility's embankment.A downstream analysis is required for all
spillways to ensure that they do not cause or exacerbate flooding downstream.Additional information is
provided in Section 8.4.1 (Downstream Analysis).
The approved discharge point must be the public stormwater system.
The minimum width of a spillway is 6 ft.The invert elevation of the spillway must be at least 12 inches
above the primary overflow outlet elevation but 12 inches below the top of the embankment.
Spillways must be constructed of concrete or riprap with an apron at the bottom that can contain and
disperse hydraulic jumps that may occur during use.The stormwater report must provide information
on the size and location of hydraulic jumps.
Spillways must be designed by a civil engineer(PE)with hydrologic and hydraulic experience.
9.1.3.4 Other Requirements
The Flow Control structure, or orifice, in a regional facility must be at an elevation that detains the
design storm. A ditch inlet with a box frame and grate (Standard Details SD6-01A and SD6-01C) must be
used as the outlet structure. Overflows must connect directly to the public stormwater system.
Ponds(private and public) must have access roads capable of carrying maintenance vehicles (such as a
track hoe and truck).A 4-ft fence and access gate around the pond is required if the ponding depth is
over 2 feet.The Engineering Design Standards provide additional requirements for access roads.
Staff gauges are required at the inlet and outlet.
Vector(mosquito) control is an important design consideration for any facility that has standing water
for extended periods of time. Bat boxes, diverse planting and other design strategies to encourage
biological controls can help to keep mosquito populations in balance.
9.1.4 Proprietary Stormwater Treatment
Proprietary stormwater treatment devices may be used for non-SFR projects if all of the following
requirements are met:
• The device is approved by the Washington Department of Ecology (DOE)TAPE (Technology
Assessment Protocol) program and has received a general use level designation (GULD)for the
water quality treatment required for the project.
• The facility design adheres to the Washington DOE TAPE constraints placed on the facility type.
• The Washington DOE TAPE constraints are provided in the stormwater report and on the
construction plans.
• The applicant has received written approval from the City Engineer during the land-use process
or prior to the submittal of the stormwater report, whichever occurs first.
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The City Engineer may require additional conditions for the projects using proprietary treatment.Their
decision is final.
9.2 SPECIFIC DESIGN STANDARDS
The following design standards are required in addition to the general design standards specified in the
previous section.
Section Stormwater Facility Section Stormwater Facility
9.2.1 _ Drywells 9.2.7 Sand Filters
9.2.2 _ Permeable Pavers 9.2.8 Swales
9.2.3 Pervious Pavement 9.2.9 Trenches and Galleries
9.2.4 Planters 9.2.10 Vegetated Filter Strips
9.2.5 Ponds 9.2.11 Water Quality Vaults
9.2.6 Raingardens 9.2.12 Wetlands
9.2.1 Drywells (Standard Detail SD1-02)
Applicability Table A drywell is an underground perforated concrete cylinder or
vault that discharges stormwater through the perforations and
Tier 1 into the surrounding soil.
Onsite Retention `,/ 9.2.1.1 Dimensions
Flow Control Maximum Depth: 16 feet for public, 8 feet for private
Water Quality Treatment Maximum Width: 4 feet
Extended Filtration
9.2.1.2 Materials
Capital Improvement ✓
Drywells must be precast concrete that conforms with ASTM
Public Improvement C478 (ASTM, 2022).
Single-Family Residential ✓ A minimum 12-inch wide ring of drain rock that complies with
Prescriptive Sizing AASHTO No.4 must be placed between the perforated section of
the drywell and the surrounding soil.
A minimum 12-inches of clean crushed rock(3/4" ) must be placed under the bottom of the drywell to
create a level base.The rock must comply with the Subsurface Drain Section in the most current version
of the ODOT/APWA Standard Specifications for Construction.
9.2.1.3 Other Requirements
Pretreatment must comply with the UIC requirements in Section 9.1.2 (General Design Standards—
Underground Injection Controls).
The perforated section of the drywell must be lower than 1)the floor elevation of basements in adjacent
properties and 2)the elevation of the surrounding property to avoid preferential pathways or piping
onto the surrounding properties.
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Soil adjacent to the drywell's drain rock must be scarified and uncompacted.
The outside edge of the drywell's drain rock must be at least 10 feet from building foundations and from
newly planted trees and large shrubs.
To provide access for maintenance,the top of the drywell must be at ground surface. A lockable lid is
required for private facilities and a manhole cover is required for public facilities.
Additional requirements are listed in the general design requirements(Section 9.1.2—UlCs).
The facility must drain within 24 hours.
9.2.2 Permeable Pavement(Standard Detail SD9-09)
Permeable pavement is a surface designed to infiltrate or treat
Applicability Table precipitation that falls on it.An underlying storage reservoir
Tier 1 beneath the pavement can be used for temporary storage. It is
not designed to treat or infiltrate stormwater from other
Onsite Retention ✓
impervious areas.
Flow Control — Permeable asphalt is an open-graded asphalt that allows
Water Quality Treatment ✓ precipitation to infiltrate into underlying soil. It uses a hot or
Extended Filtration warm asphalt mix where the amount of fines is reduced from an
impervious asphalt mix to create a pavement with more voids
Capital Improvement' `/ that can provide infiltration.
Public Improvement Permeable concrete is a concrete with interconnected voids (15
Single-Family Residential ✓ to 33%)that allow water to flow through the material under
Prescriptive Sizing
gravity(ACI, 2023). It is comprised of open-graded coarse
aggregate, cement, little or no fine aggregate, and water.
1—Requires Prior City Approval
9.2.2.1 Location
Permeable pavement can be used for pathways, access roads (maintenance or emergency), and
driveways.
Permeable pavement cannot be installed:
• In the public ROW without written City Engineer approval obtained during the land-use process
or the submittal of construction plans,whichever occurs first;
• Over culverts or bridges;
• Over areas of fill;
• Above the ground floor of a multi-level parking area;
• In areas of frequent sharp turns, i.e., parking lots;
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• In areas of frequent winter maintenance where de-
icing or anti-icing materials are used e.g.
�n-
magnesium chloride, sand,gravel, rock salt; k. •
• At industrial sites; or 1 � V
K{
• At commercial sites using or storing petrochemicals • {
or hazardous materials.
9.2.2.2 Slopes a • .,•-
Slopes must be 6 percent or flatter. F '� y j
Check dams or concrete weirs must be installed in the
storage course for slopes>_3/. _ V ,6
9.2.2.3 Materials s r }.;
Permeable pavement located adjacent to a road or building
foundation must have a 30-mil PVC or HDPE liner or cast-in- '"°
place concrete curb that extends beyond the depth of the road base or building foundation.
A 3-inch choker course must separate the soil layer from the storage course. It must be comprised of
clean rock(3 "to 1/2")that complies with the Subsurface Drain Section in the most current version of the
ODOT/APWA Standard Specifications for Construction.
A storage course is optional for permeable pavement. If used, it must be a clean angular open-graded
rock ranging from 1-%2" to 3 "that complies with the Subsurface Drain Section in the most current
version of the ODOT/APWA Standard Specifications for Construction.The depth for vehicular areas such
as parking lots or driveways must range between 12 to 24 inches to provide structural support.
9.2.2.4 Other Requirements
Permeable asphalt design must follow the Porous Asphalt Concrete Section in the most current version
of the ODOT/APWA Standard Specifications for Construction.
Permeable concrete projects must be designed by a civil engineer(PE)with a minimum of 5 years of
experience designing permeable concrete systems.The specifications and their source must be
submitted with the stormwater report.
The elevation of the top of the storage course must be below the elevation of adjacent properties and
the finish grade of basements in adjacent properties.The bottom elevation of the storage course must
be at least 4 inches below the elevation of the frost line.
Underdrains are not permitted in permeable pavement systems.
While important for all stormwater facilities, proper installation and regular maintenance is critical for
these facilities.
9.2.2.5 Construction Notes
During construction,the location must be protected from sediment and runoff.
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The subgrade must be protected from compaction,truck traffic, material storage, and construction
equipment.
9.2.3 Pervious Pavers (Standard Detail SD9-10)
Pervious pavers are flagstones or pavers.They
have a gap that is filled with high-infiltration A
material such as sand. _r
Permeable interlocking concrete pavement (PICP) IIII
and grid systems are types of permeable pavers.
PICPs are solid, precast, modular units that are
made with a high-strength Portland Cement
concrete and placed on an open-graded bedding
course.Joints are filled with permeable
aggregate. .2
";.:Zr;y.
Grid systems are used for pedestrian and low -."
traffic areas such as patios, driveways, emergency ?'.a
access lanes, and parking areas used for '
temporary(overflow) event parking.A high-
strength `°
concrete (5,000 psi or greater) or plastic grid is filled with pea gravel or sand.
Pervious paver designs treat and infiltrate only the precipitation that falls on them. Stormwater from
other impervious areas is not allowed to flow onto permeable pavers.
Applicability Table Pervious pavers are not suitable:
Tier 1 • In the public ROW unless pre-approved by the City Engineer in
1( writing;
Onsite Retention
• Over culverts or bridges;
Flow Control • Over areas of fill;
Water Quality Treatment `,/ • Above the ground floor of a multi-level parking area;
Extended Filtration • In areas of frequent winter maintenance where de-icing or
Capital Improvement' ✓ anti-icing materials are used e.g. magnesium chloride, sand,
gravel, rock salt
Public Improvement
• At industrial sites; or
Single-Family Residential ✓ • At commercial sites using or storing petrochemicals or
Prescriptive Sizing hazardous materials.
1—Requires Prior City Approval
9.2.3.1 Slopes
Slopes must be 6 percent or flatter.
Check dams or concrete weirs must be installed in the storage course for slopes>_ 3%.
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9.2.3.2 Materials
Pervious pavers located adjacent to a street, road, or building foundation must have a 30-mil PVC or
HDPE liner or cast-in-place concrete curb that extends beyond the depth of the road base or building
foundation.
Edge Restraints
• To prevent lateral migration of the pavers, an edge restraint is required.
• The edge restraint for SFR applications must be either a spiked metal edge restraint or a cast-in-
place curb.The edge restraint for non-SFR applications must be a cast-in-place curb that is at least
6 inches wide and 12 inches deep.
Leveling Course
• The leveling course must be 1 to 3-inches thick and consist of clean sand.
Choker Course
• A 3-inch of clean rock ranging from %"to%" and complying with the Subsurface Drain Section in
the most current version of the ODOT/APWA Standard Specifications for Construction.
Storage Course(optional)
• The aggregate storage course must be a clean angular open-graded rock ranging from 1-Y2"to 3/"
that complies with the Subsurface Drain Section in the most current version of the ODOT/APWA
Standard Specifications for Construction.
• The depth for pervious pavers must range between 6 inches to 36 inches in vehicular areas, such
as parking lots or driveways,to provide structural support.
• The depth of the storage course for PICPs can vary from 6 to 12 inches. Grids must have a storage
course of 6 inches.
9.2.3.3 Other Requirements
The elevation of the top of the storage course must be below the elevation of adjacent properties and
the finish grade of basements in adjacent properties.The bottom elevation of the storage course must
be at least 4 inches below the elevation of the frost line
Underdrains are not allowed for pervious paver systems.
While important for all stormwater facilities, proper installation and regular maintenance is critical for
these facilities.
9.2.3.4 Construction Notes
During construction,the location must be protected from sediment and runoff.
The subgrade must be protected from compaction, material storage, and construction equipment.
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9.2.4 Planters (Standard Details SD9-12 and SD9-13)
Planters are vegetated facilities with four structural
Applicability Table walls.They require minimal space because of their
1(Infiltration vertical walls. Filtration (flow-through) planters can be
Tier 2 (Filtration) constructed adjacent to building foundations.
Onsite Retention Infiltration Only 9.2.4.1 Dimensions
Flow Control I Filtration only Treatment areas must be at least 3 feet wide.
Water Quality Treatment ✓ The minimum freeboard must be 6 inches for facilities
Extended Filtration Filtration only treating impervious areas that are 3,000 sq ft or
greater.The minimum freeboard for facilities treating
Capital Improvement ✓ less than 3,000 sq ft is 3 inches.
Public Improvement ✓
The maximum freeboard is 12 inches.
Single-Family Residential ✓
✓ The ponding depth must be between 0.5 ft and 1 ft.
Prescriptive Sizing
The soil media depth must range from 1.5 ft to 2 ft.
9.2.4.2 Materials
Planter walls and bottoms must consist of concrete with a 28-day compressive strength of 3,000 psi.
Planter walls and bottoms must be 6 inches thick concrete. *�0
Planters located next to roads or streets must include a 30-mil
4
PVC or HDPE liner on the street/road side of the planter. 411
I EI
A storage course is optional for an infiltration facility but �� ;'16 �;br; IT _T
required for a filtration facility. ,' �
An underdrain is prohibited for infiltration facilities but required '. `ti ��� } � ,'T
for a filtration facility. Requirements are provided in the general e qq,
4,4
design criteria in Section 9.1.1 (Vegetated Facilities) � s , �
9.2.4.3 Other Requirements ter n w` 1.
Multi-celled planters(see Standard Detail SD9-01) can be used a. � :: " , K. ,k , ,rt
on sloping properties via two or more flat areas separated by \N,iv e.
weirs that allow water to drop with the slope.All cells must f ' 44
^ y�
have a dissipation pad to reduce erosion of the soil.The
overflow must be located in the lowest cell of the facility. 9' I' ++
The building foundation must NOT be used as a wall for a storm water planter.
-66-
Planters must discharge stormwater within a 24-hour time period.
Pedestrian safety and access must be incorporated into the planter design. Ensure that planters located
next to parking areas have clearance for pedestrians exiting vehicles.
Water quality planters shall not be located downstream of detention.
Additional requirements,such as storage layers and liners, are listed in the general design
requirements(Section 9.1.1—Vegetated Facilities).
9.2.5 Ponds
Applicability Table Stormwater ponds are a good choice where there is a
large contributing area and where they can be easily
Tier 3 accessed for maintenance. Ponds approved for use
•
Infiltration and include detention ponds, infiltration ponds, and
Onsite Retention Retention Only retention ponds.
Flow Control `( Detention ponds temporarily store water for 24 hours
Infiltration and and use an orifice to control the discharge rate from the
Water Quality Treatment Retention Only pond.There may be incidental infiltration but soils are
Extended Filtration 1/ not adequate for infiltration.
Capital Improvement ✓ Infiltration ponds temporarily store stormwater while it
infiltrates into the soil. Infiltration ponds must be sized
Public Improvement ✓ for onsite retention.They differ from raingardens in size
Single-Family Residential ✓ and ownership. Raingardens are generally owned by
one property owner whereas ponds are generally
Prescriptive Sizing I
owned and maintained by a business, home owner's
association (HOA), or neighborhood association.
Retention ponds have a permanent pool of standing water and must be designed with aeration to avoid
stagnation and minimize disease vectors during the dry summer months. Retention pond may be used
to provide Flow Control if they are designed with additional storage to provide detention of the design
storm.The orifice must be located at an elevation that is above the permanent pool.
9.2.5.1 Dimensions
Include two cells, with the first cell (sediment forebay) containing approximately 10%of the design
surface area.A pollution control manhole can substitute as a sediment forebay.
Sides slopes must be 3H:1V or gentler.
The length to width ratio must be 3:1 or greater.
The length from the inlet to the outlet must be maximized to provide the greatest residence time.
For retention ponds,the maximum permanent pool depth is 2 feet.The depth must not exceed 6 feet
during the design storm.
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Berm embankments must have a minimum top width of 6 feet.
Ponds must be designed by a civil engineer(PE)with hydrologic and hydraulic experience.
9.2.5.2 Other Requirements
Ponds cannot be constructed in floodplains or waterways.
Drawdown time for detention ponds and infiltration ponds is 24 hours. Retention ponds must revert to
the permanent pool depth within 24 hours.
Additional requirements are listed in the general design standards(Section 9.1.3—Regional
Facilities).
9.2.6 Raingardens (Standard Details SD9-15 and SD9-16)
Applicability Table Rain gardens are vegetated facilities with gently sloping sides.
While generally circular in shape, they can adapt to any area.
1 (Infiltration) Linear rain gardens may look similar to swales; however,
Tier 2 (Filtration) swales gently slope longitudinally as water is conveyed
Onsite Infiltration through the swale.
Retention Only
They are ideal for residential and commercial sites, within
Flow Control Filtration Only parking lots, and along roadways.
Water Quality
Treatment 1/ Sculpture is allowed in a rain garden as long as the treatment
area is increased to compensate for the sculpture's footprint.
Extended Filtration Filtration Only
Capital Improvement ✓ 9.2.6.1 Dimensions
Public Improvement ✓ Raingardens must have a flat bottom of 2 ft x 2 ft with a
Single-Family minimum cross-slope of 1%.
Residential ✓
Sides slopes must be 3H:1V or flatter.
Prescriptive
Sizing ✓ The ponding depth can range from 0.5 ft to 1 ft but the facility
must empty within 24 hours.
The maximum freeboard is 12 inches.The minimum freeboard must be 6 inches for facilities treating
impervious areas that are 3,000 sq ft or greater.The minimum freeboard for facilities treating less than
3,000 sq ft is 3 inches.
-68-
9.2.6.2 Other Requirements
The design must ensure that the elevation of the overflow is lower than the invert elevation of the inlets
to the facility.The design must also maximize the distance between the overflow structure and the inlet
structures.
Raingardens can be used on sloping properties via two or ;� `y
�s
more flat areas separated by weirs (Detail Drawing SD9-01)
that allow water to drop with the slope. Standard detail I' ` =' ,_,`` '``
drawing SD9-07 provides the additional requirements .�
1 ,,„, a r am,+ r £ ` y
needed for a multiple-celled facility.All cells must have a d ,
dissipation pad to reduce erosion of the soil, prevent short-
circuiting of the flow, and preserve structural integrity.The •
�� -
overflow must be located only in the last cell.
Raingardens located next to streets and roads must include a '"��.: r,i "��s;'► :. :
30-mil PVC or HDPE liner on the street road side of the %:'•i; „+�, •''l '�
raingarden to minimize degradation of the road base.
Additional requirements, such as storage courses and liners, are listed in the general design
standards(Section 9.1.1—Vegetated Facilities).
9.2.7 Sand Filter
Sand filters may be horizontal or vertical. Both require
Applicability Table a flow spreader and a sand bed.Vegetation is optional.
Tier 3 A horizontal sand filter is a shallow rectangular facility
Onsite Retention that allows stormwater to be filtered through a sand
Flow Control and gravel bed. A vertical sand filter is a tall
- rectangular facility that uses hydraulic head for
Water Quality Treatment filtration through the sand bed.
Extended Filtration Sand filters require written approval from the City
Capital Improvement ✓ Engineer and the Public Works Director obtained
Public Improvement' during the land-use process or prior to the submittal of
✓
construction plans, whichever occurs first.
Single-Family Residential
Prescriptive Sizing
1-With prior City Engineer Approval Only
9.2.7.1 Dimensions
The width must be 2 feet or greater.
The length must range from 3 ft to 15 ft.
The depth of the sand course must be 1 foot or greater.
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The length to width ratio must be 2:1.
The minimum ponding depth is 1 foot.
The minimum freeboard must be 6 inches for facilities treating impervious areas that are 3,000 sq ft or
greater.The minimum freeboard for facilities treating less than 3,000 sq ft is 3 inches.The maximum
freeboard is 12 inches.
The slope must range from 0 to 0.5%towards the overflow for horizontal facilities and towards the
center for vertical facilities.
9.2.7.2 Materials
The walls and bottom of a sand filter must be made of 6-inch thick concrete with a 28-day compressive
strength of 3,000 psi.
Using a building's foundation as a 4t'wall for a sand filter is prohibited.
The sand bed must consist of a medium sand meeting the size gradation (by weight) given in Table 10.
The contractor shall obtain a grain size analysis from the supplier to certify that the No. 100 and No. 200
sieve requirements are met.The certification must be provided as part of the post-construction
submittal.
Table 10.Sand Media Specifications
U.S.Sieve Number Percent Passing
4 95-100
8 70-100
16 40-90
30 25-75
50 2-25
100 <4
200 <2
From:King County(1998)and Washington DOE(2024).
A 3-inch choker course must separate the sand course from the storage course,with clean rock ranging
in size from %"to 1/2", and comply with the Subsurface Drain Section in the most current version of the
ODOT/APWA Standard Specifications for Construction.
The storage course must range from 1 foot to 2 feet, with clean rock ranging in size from 1-Y2"to 3/"
that complies with the Subsurface Drain Section in the most current version of the ODOT/APWA
Standard Specifications for Construction.
A 30-mil PVC or HDPE liner is required along the bottom and sides of the facility. It must extend to the top
of the ponding depth.
A perforated pipe that complies with Standard Detail SD9-11 is also required.
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9.2.7.3 Other Requirements
Pretreatment must be provided using a separate compartment, pollution control manhole, or sumped
and snouted catch basin.
For vertical facilities, the hydraulic head must be 4 ft or greater.
The overflow for a horizontal facility must be a beehive (see Standard Details SD8-01 and SD8-02).
9.2.7.4 Construction Notes
After construction, flood the facility with 10-15 gallons of clean water per cubic foot of sand to
consolidate the sand course.
9.2.8 Swale (Standard Details SD9-19 and SD9-2O)
A swale is a gently sloped,vegetated channel.They
Applicability Table differ from ditches in that they treat stormwater and
1 (Infiltration) are designed for a low velocity whereas ditches only
Tier 2(Filtration) convey stormwater and are designed for high
stormwater velocities.
Onsite Retention Infiltration only
Swales differ from linear raingardens in that they have
Flow Control ✓ flatter side slopes and lower flow depths.They work
Water Quality Treatment ✓ well along roadways, driveways, and parking lots.
Extended Filtration Filtration Only
9.2.8.1 Dimensions
Capital Improvement ✓
The minimum length is 100 feet. Sites which cannot
Public Improvement accommodate a minimum 100-foot length should be
Single-Family Residential ✓ designed as rain gardens or planters.
Prescriptive Sizing The minimum bottom width is 3 feet.
Side slopes must be 4H:1V or flatter
Longitudinal slopes can range from 0.5 to 4 percent.
The maximum flow depth is 4 inches.
The minimum freeboard must be 6 inches for facilities treating impervious areas that are 3,000 sq ft or
greater.The minimum freeboard for facilities treating less than 3,000 sq ft is 3 inches.The maximum
freeboard is 1 foot
9.2.8.2 Other Requirements
Velocity must be less than 3 ft per second and provide a residence time of 9 minutes or longer. Rock
check dams spaced a maximum of 10 ft apart, can be used to decrease velocity through the facility.
Swales that are constructed with a storage course must provide weirs instead of check dams to minimize
the possibility of creating preferential flow path.
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Inlets must conform to the requirements of Detail Drawing SD9-02 for swales receiving stormwater from
flatwork or streets.
Swales located next to roads must include a 30-mil PVC or HDPE liner on the street side of the swale to
minimize degradation of the road base.
Multi-celled swales must be used for roads with slopes greater than 4 percent (see Standard Detail
Drawing SD9-07).They must include concrete weirs instead of check dams to avoid preferential flows
through the facility.
Swales must not be located downstream of detention.
Additional requirements, such as storage layers and liners, are listed in the general design
standards(Section 9.1.1-Vegetated Facilities).
9.2.9 Trenches and Galleries (Standard Detail SD9-06)
A trench is a rectangular facility that infiltrates stormwater
Applicability Table discharging from a perforated pipe laid in a gravel trench.
Tier 1
An infiltration gallery infiltrates stormwater through a perforated
Onsite Retention ✓ pipe placed in rock that is structurally supported to provide more
storage than a trench. It can consist of multiple rows of storage.
Flow Control
Water Quality Treatment 9.2.9.1 Dimensions
Extended Filtration The storage course depth for infiltration trenches ranges from 1
Capital Improvement) I/ to 3 feet. It ranges from 2 feet to 7 feet for galleries and must
comply with manufacturers specifications.
Public Improvement
— The facility width is a minimum of 2 feet for infiltration trenches
Single-Family Residential ✓ and 4 feet for infiltration galleries.
Prescriptive Sizing The depth of the overlying soil for infiltration trenches ranges
1-With approval of UIC permit manager from 1 to 3 feet.The depth for galleries will depend on
manufacturer requirements.
9.2.9.2 Materials
A 3-inch choker course must separate the soil overlying the trench or gallery from the storage course,
with rock ranging in size from %"to%z", and comply with the Subsurface Drain Section in the most
current version of the ODOT/APWA Standard Specifications for Construction. If placed below a
driveway,the pavement section can substitute for the choker course however the base layer for the
driveway cannot be used as additional storage during design.
The perforated pipe (see Standard Detail SD9-11) used to discharge stormwater into the facility must be
placed within the top third of the storage course for trenches and in the upper section of the structural
support for galleries.The elevation for a gallery is dependent on the manufacturer specification.
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The storage course must consist of clean rock(1-1/2"to 3 " )that complies with the Subsurface Drain
Section in the most current version of the ODOT/APWA Standard Specifications for Construction.
9.2.9.3 Other Requirements
Trenches cannot be located where they will be subject to vehicular traffic. Galleries, however, may be
placed in residential driveways and parking lots because of their structural support.
The top of the infiltration gallery or trench must be at the same elevation as the adjacent properties and
lower than the floor elevation of basements in adjacent properties to avoid preferential pathways or
piping onto adjacent properties.
9.2.9.4 Construction Notes
• Rock for the storage course must be placed into a gallery with equipment located next to, but
not in,the facility in order to protect the infiltration capacity and structural integrity of the
perforated pipe and structural support.
• Dump trucks cannot be used to push rock into the storage course.
• To protect the perforated pipe and structural support, rock should be leveled parallel to the pipe
or structures.
9.2.10 Vegetated Filter Strips ((Standard Detail SD9-05)
Applicability Table A vegetated filter strip is a vegetated area adjacent to an
Tier 3 uncurbed impervious area such as a sidewalk or driveway.
Stormwater is dispersed evenly across the entire width at a low
Onsite Retention velocity and depth.
Flow Control Sidewalks and other walkways may be reverse-sloped and use
Water Quality Treatment ✓ vegetated filter strips for stormwater management. Patios less
than 500 sq ft may provide a 0.5%slope in order to use a
Extended Filtration ✓
vegetated filter strip to manage stormwater.
Capital Improvement ✓
Vegetated filter strips are appropriate for all soil types and may
Public Improvement be located on a range of site conditions from full sun to full
Single-Family Residential ✓ shade.
Prescriptive Sizing
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9.2.10.1 Dimensions
The length of a vegetated filter strip can range between 5
to 100 feet as measured in the direction of flow(see ,c .
Figure 14). •�a� e� _
The width of the facility must extend 6 inches beyond the Atha
edges of the impervious area discharging to the facility.
Alternatively,the impervious area may be constrained
with an edging that is at least 1 inch above adjacent
surfaces to ensure that flows do not bypass the facility. Atc
9.2.10.2 Other Requirements �Ph
g�h
Flow depths cannot exceed 1 inch and flow velocities
cannot exceed 0.5 ft/sec.
Figure 14. Vegetated Filter Strip
The slope of the facility can range between 0.5 and 10
percent as long as the flow is distributed evenly along the length of the vegetated filter strip.
• if the slope is between 3 and 5 percent or the width of the impervious area discharging to the
facility is greater than 100 ft, a rock strip (1 ft X 1 ft X 0.5 ft) or a non-galvanized trench drain is
required across the length of the facility to disperse the flow.
• if the slope is over 5%, non-galvanized interior trench drains or 1-ft X 1-ft X 0.5 ft gravel check
dams must be constructed along the interior length of the facility to reduce erosion and velocity
and to re-disperse the flow.
Vegetated filter strips must be a minimum of 50 feet from waterways.
Additional requirements, such as soil and plants, are listed in the general design standards
(Section 9.1.1—Vegetated Facilities).
9.2.11 Water-Quality Vaults
Applicability Table Water-quality vaults can be used for non-SFR and capital
Tier 3
improvement projects.They cannot be used to satisfy public
improvements required as a condition of private development.
Onsite Retention
✓ Water-quality vaults are used to reduce solids. Depending on the
Flow Control type of filter used, they can reduce metals, oil, phosphorous, or
Water Quality Treatment ✓ sediment.They must be constructed of reinforced concrete with
the cartridge filters designed according to the constraints of the
Extended Filtration 1( Washington DOE TAPE program for the targeted pollutant (see
Capital Improvement ✓ Section 7.5—Water-Quality Limited Waterways).The
Public Improvement Washington DOE TAPE constraints for the targeted pollutant(s)
must be included in the stormwater report.
Single-Family Residential
Prescriptive Sizing
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9.2.12 Wetlands, Constructed
Applicability Table Constructed wetlands are designed to emulate natural
Tier 3 wetlands.They have irregular shape,variable water
depths, and side slopes.They have standing water for part
Onsite Retention of the year, are shallower than ponds, and have mottled
soil due to long periods of saturated conditions during the
Flow Control ✓
winter.
Water Quality Treatment ✓
Constructed wetlands present an opportunity to integrate
Extended Filtration -
wildlife habitat and a public amenity into the landscape.
Capital Improvement ✓
Vector(mosquito) control is an important design consideration
Public Improvement ✓ Bat boxes, diverse plants, and other design strategies to
-
Single-Family Residential ✓ encourage biological controls can help to keep mosquito
populations in balance.
Prescriptive Sizing
9.2.12.1 Dimensions
The minimum bottom width is 3 feet.
The minimum length to width ratio is 2:1.
The maximum ponding depth is 3 feet with an average ponding depth of 2.5 feet.
Side slopes below the design ponding depth must be 5H:1V or flatter.They must be 3H:1V or flatter
above the design ponding depth.
9.2.12.2 Other Requirements
Constructed wetlands must be tear-drop shaped with the inlets at the narrow end to minimize dead
zones and facilitate flow.The outlet and spillway must be at the opposite end to maximize treatment.
Wetlands must either have aerators installed or be oriented with the prevailing summer winds to
minimize anoxic conditions.
Permanent water depth in a wetland should vary in the different cells. For design purposes,the pond
should be designed to have standing water for at least 10 months of the year.
Pretreatment is required and can take the form of a pollution control manhole or a sediment forebay. If
using a sediment forebay, it must contain 10 percent of the design volume. A sediment forebay provides
a clear visual indicator of when maintenance is needed.
Additional requirements, such as vegetation and spillways, are listed in the general design
standards(Section 9.1.3—Regional Facilities).
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10 CONVEYANCE DESIGN
Conveyance systems carry stormwater from one location to another through a series of catch basins,
pipes, and manholes.The requirements for conveyance system design is primarily provided in the City's
Engineering Design Standards.The information contained in this Chapter are additional requirements.
Discrepancies in requirements between the SWMM and the Engineering Design Standards will default to
the requirement that is most protective of water-quality.
Conveyance design must account for full build-out.The assumptions and parameters used for full build-
out are listed in Section 8.4 (Capacity Analyses).
10.1 DETENTION
Detention pipe and detention vaults are allowed for non-SFR projects and must follow the requirements
of the Engineering Design Standards with the following changes:
• The minimum diameter for private detention pipes is 36 inches.
• The CN used for pre-development flows calculated during design must be 70.
• A pollution control manhole or water-quality vault is required at the inlet to the detention tank
or vault to reduce sedimentation in the tank or vault.
• A flow control manhole is required at the outlet to the detention tank or vault to maintain pre-
development flowrates.
• O&M Plans for detention pipes and vaults must state that a current confined space certification
is required for all people completing maintenance on the facilities.
10.2 CONVEYANCE STRUCTURES
The Engineering Design Standards contain many of the design requirements and material specifications
for conveyance systems. Public stormwater structures must be designed in conformance with the
Engineering Design Standards and be able to convey stormwater generated from the design storm in the
Engineering Design Standards for the entire upstream catchment. Full build-out, as defined in Section
8.4 (Capacity Analyses), must be assumed for the design.
10.2.1 Alignment and Location
Storm lines must run in straight lines, with a constant slope, material, and diameter from manhole to
manhole.The minimum cover for stormline is 3 feet or at a depth that is sufficient to protect it against
damage from construction loads or final traffic loads,whichever is greater.
In public and private streets, new or replaced stormwater mainline locations shall follow these
requirements to the extent possible:
• On the opposite side of the water system,
• On the south or west side of the street, and
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• In the pavement for uncurbed streets.
If the water system is, or can be, located in the center of the street then stormwater mainlines must be
located on the opposite side of the wastewater system.
The Engineering Design Standards provide additional information for utility separations in its
Wastewater Chapter.
10.2.2 Private and Public System Connections
Private systems are not allowed in the public ROW and must connect to the public system at a 90° angle.
A right-of-way permit is required for all private system connections to the public stormwater system.
Public systems must be located in the ROW with the exception of treatment or detention facilities which
may be located on City-owned properties. Private stormwater laterals must connect to the public
system at a 90°angle.
The public system must not discharge to a private system.
The public stormwater system must be located in the public ROW and cannot discharge to a
private system.
10.2.3 Stormline and Manholes
The Engineering Design Standards provide a majority of the standards to be used when designing a
pipeshed.The following standards are in addition to the requirements of the Engineering Design
Standards. If a conflict arises, the standard that is most protective of water-quality shall take
precedence.
10.2.3.1 Stormline Size
Public stormwater pipes shall be, at a minimum, 10-inches from inlets and catch basins to mainlines.
Mainlines must be a minimum of 12 inches but must be sized to convey flows from the upstream
pipeshed at full buildout, as defined in Section 8.4 (Capacity Analyses), during the design storm event
listed in the Engineering Design Standards with the exception that the minimum design storm event is a
25-yr 24-hr storm event. Stormline cannot be smaller than that used in the upstream pipeshed.
Private stormline shall be a minimum of 4 inches in diameter and be comprised of material meeting the
requirements for conveyance pipe in the Engineering Design Standards.
At increases in pipe diameter,the crown of the upstream pipe must not be lower than the crown of the
downstream pipe.The invert of the upstream pipe must provide a minimum drop of 0.2 ft from the
invert of the outlet pipe.
10.2.3.2 Video
All new and replaced public stormline must be videoed to ensure quality construction and must comply
with the Video Pipe Inspection Section in the most current version of the APWA/ODOT Standard
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Specifications for Construction.The video must be submitted to the Engineering Development Review
staff or CIP Project Manager as part of the post-construction submittals.
10.2.4 Catch Basins and Inlets
In addition to the spacing required in the Engineering Design Standards, inlets and catch basins must be
provided at intermediate locations a) where the design flow at the curb line (or berm) exceeds 3 inches
in depth or 3 feet in width (as measured from the curb face or berm) whichever is less and 2) at the low
point for all cul-de-sacs and dead-end streets with a descending grade.
Water-quality snouts are required for all new and replaced catch basins.The snout must be attached to
the outlet pipe.
10.2.5 Ditches
Ditches provide stormwater conveyance only and are not designed to provide water-quality treatment.
To prevent erosion, ditches must:
• Have sides slopes of 3H:1V or flatter.
• Be sized to carry the design storm at non-erosive velocities.
• Maximum design depth must be 1 ft below adjacent roads.
• If the slope is 4%or greater,the design must provide:
o 6-inch concrete weirs, gabion baskets, or gabion mattresses that do not exceed a 1-ft
elevation drop and,
o energy dissipation at the elevation drop (see Detail SDX-XX Multiple-Celled Facilities).
Quarry spalls may be used for the bottom of the ditch however the side slopes above bank-full
conditions (see Definitions) must be seeded with native grasses and shrubs. If planted, trees must be
located at top of bank and on the south and west sides to assist with temperature TMDL allocations.
10.2.6 Culverts and Bridges
Designs for culverts and bridges must meet these design standards, the Engineering Design Standards,
Oregon Department of Fish and Wildlife (ODFW) criteria, and DSL requirements.Where the
requirements conflict, the criteria most protective of water-quality applies.
ODFW criteria for fish passage (physical and velocity barriers) shall be met for all perennial waterways
and wetlands. Riprap placed to protect abutments shall be placed only below bankfull depth and shall
not constrict channel flow.
Designs must be submitted to DSL and the ODFW for their review. A copy of their decisions and
requirements must be submitted to the Engineering Development Review staff with other land-use and
construction plan submittals.
10.2.6.1 Bridges
Design storms for bridges are listed in the Engineering Design Standards with the following changes:
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• For streams without a FEMA-designated 100-year floodplain, bridges must convey the 100-yr
24-hr storm event.
• The vertical clearance between the design water surface and the bottom of the bridge deck shall
be a minimum of 2 feet.
10.2.6.2 Culverts
Design storms for culverts are listed in the Engineering Design Standards. Culverts must match the
existing slope and orientation of the ditch or waterway.
Bottomless culverts shall be used for crossing wetlands and perennial streams. Bottomless culverts shall
provide clearances that meet the requirements of regular culverts.
Culverts shall be designed such that the headwater a) does not exceed 0.8 times the culvert diameter
OR b) remains 1 foot below the subgrade of the road,whichever is less.
The minimum culvert diameter is 10 inches for private culverts and 12 inches for public culverts of
normal length and depth.A 24-inch minimum diameter is required for culverts that are 150 ft long or
are under 15 ft or more of fill. The culvert diameter must equal or be larger than the diameter of
upstream culverts.
Culverts must be made of materials with a 75-year design life. Due to low service life (ODOT, 2014),
galvanized steel culverts are prohibited. Concrete culverts are preferred over metal or plastic due to
their low maintenance and fewer adverse effects to water-quality.
To prevent under-sizing and to protect riparian corridors and property within the City, culvert
replacements must adhere to these requirements.
10.3 OUTFALLS AND OFFSITE STORMWATER DISCHARGES
All stormwater must be treated to reduce suspended solids and phosphorous by 80% prior to discharge
offsite (see Section 7.5).
Discharges to ditches and waterways must comply with the City's outfall detail drawing (SD9-08).
Sheetflow offsite cannot be at erosive velocities or exceed 100 ft before entering the public stormwater
system or a waterway.
To protect existing wetlands, discharges cannot increase the pre-development water surface elevation
by more than 1 inch.
10.3.1.1 Location
The point of discharge offsite and outfall locations must be approved by the City Engineer during the
land-use process or the submittal of construction plans, whichever occurs first. In general,the following
criteria apply:
• Discharge cannot be to another property's stormwater facility.
• For maintenance reasons, outfalls can't be under a bridge, in a culvert, or connect as a blind tee.
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• To prevent slope failure, outfalls cannot be located within 200 ft of steep slopes unless a downslope
pipe or other means of velocity reduction are installed to the toe of the slope to prevent erosion and
hydromodification (see next section—Velocity).
• Flow spreaders cannot be used to discharge on slopes greater than 5%.
10.3.1.2 Velocity
Stormwater discharged offsite must have energy dissipation adequately designed to prevent erosion at
the point of discharge. Design calculations must include the peak discharge and the peak flow duration.
The City Engineer may require additional energy dissipation based on these factors and the soil type of
the receiving area.
10.4 PUBLIC CONVEYANCE EXTENSION
Extensions of the public stormwater system required as a condition of a project shall be extended to the
far side of the property, i.e. "to and through" to allow connection for upstream properties. Except as
otherwise provided,the extension of the public conveyance systems to serve any parcel or tract of land
shall be done by and at the expense of the property owner or applicant.
All extensions must be constructed in the public ROW and adhere to the stormwater requirements of
the Engineering Design Standards.
Extensions must be sized for a built-out scenario using the assumptions and parameters detailed in
Section 8.4(Capacity Analyses).
10.5 EASEMENTS
The requirements for easements, access roads, and access pathways are primarily provided in the
Engineering Design Standards.Access roads are required for all stormwater facilities that require
mechanized equipment for maintenance or that are located more than 150 feet from the public ROW.
Access pathways must obtain prior written approval from the City Engineer during the land-use process
or the submittal of construction plans,whichever occurs first.
Easements for railroad crossings shall be obtained by the applicant, and all terms for the easements
shall be met by the applicant and contractor.
Utility construction within easements shall minimize land disturbance, especially to trees and other
vegetation.Any disturbed areas within easements shall be stabilized and restored to the condition prior
to development unless requirements more protective of water-quality are required through the
municipal code.
All private storm lines in easements shall be explicitly labeled "Private" on the plat.
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10.6 ENCROACHMENTS
An encroachment permit is required for private structures, pavement, retaining walls,vegetation, or
landscaping located in the public ROW or in a public stormwater easement.
Encroachments are not permitted in areas 1) with a history of flooding, 2) that require frequent
maintenance problems, or 3) used as an access road or pathway to a stormwater system.
The City Engineer may include additional requirements as a condition of an approval.
The approval or denial of an encroachment by the City Engineer is final.
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11 MAINTENANCE OF STORMWATER FACILITIES
Stormwater facilities, private and public, must be maintained to preserve the treatment capacity and
comply with Flow Control requirements.The responsibility for maintenance is determined during the
land-use process or the submittal of construction plans, whichever occurs first. Entities responsible for
O&M of a stormwater facility must be listed on the recorded O&M Plan. Public facilities constructed as a
result of the capital improvement program or as a condition of private development become the City's
responsibility after the warranty period is completed and the City has formally accepted the facility.
11.1 OPERATIONS AND MAINTENANCE PLANS
An O&M Plan is required for all projects required to provide stormwater
O&M Plans must state management.The O&M Plan must describe how to properly maintain
that unmaintained each stormwater facility,the frequency of maintenance, and the
facilities can result in a responsible party.The maintenance of access roads and pathways must
required replacement be included in the O&M Plan.
of the facility.
Developers must record O&M Plans for private stormwater facilities in
the County of Record and provide a copy of the recorded O&M Plan
(with the County stamp)to the Engineering Development Review staff prior to receiving approval of the
final ESC inspection. Public facility O&M Plans for water-quality vaults and proprietary treatment
facilities must be provided to the Engineering Development Review staff or CIP Project Manager prior to
City acceptance of the facility.
The cover sheet required for the O&M Plan must be obtained from the Engineering Development
Review staff. Appendix D contains a maintenance template for use with the cover sheet.
11.2 FACILITY ACCESS
An access road or access pathway must be constructed when public stormwater facilities cannot be
accessed from the public ROW with industry-standard maintenance equipment.An access road is
required for mechanized maintenance and an access pathway is required for facilities that use hand
tools, do not require mechanized maintenance, and which are no farther than 150 ft away.The
Engineering Design Standards contain the design standards for access pathways and roads.
11.3 INSPECTIONS
Inspection frequency depends on the type of stormwater facility but must be completed a minimum of
once per year or when:
• The system does not drain within 24 hours or is otherwise not operating as designed.
• Nuisance conditions are present. Nuisance conditions include, but are not limited to, overflow
from smaller storms, stagnant water with algae, insect breeding, odors, discarded debris, or
safety hazards.
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11.3.1 Inspection Records
The owner or responsible party identified in the O&M Plan is required to keep all records of
maintenance.The responsible party must document repairs and keep the records for a minimum of five
years.The records may be kept electronically but must be available to the City Engineer upon request.
11.3.2 City Inspections
The City reserves the right to inspect private facilities to confirm that they are functioning as designed.
Examples of inspections may include but are not limited to:
• Routine inspections All storm water management
• Random inspections facilities, whether located on
• Inspections based upon complaints or other notice of private or public property,
possible violations shall be accessible for City
• Joint inspections with other agencies inspecting under inspection.
environmental or safety laws
• Inspection of facilities operating under a Partial Letter of
Acceptance
11.3.3 Property Sale and Facility Ownership Transfer
When ownership of public stormwater management facilities are transferred to and accepted by the
City,the transfer shall include all maintenance and access easements.
If a property is transferred to another owner,the responsible party shall:
• Inform the new owner(s) or responsible party of the existence of private stormwater facilities on
the site,their restrictions (including design capacity and setbacks), and the requirement to
inspect and maintain them
• Provide the new owner with a copy of the maintenance records documenting the facility
inspections and any repairs completed on the facility.
11.4 MAINTENANCE
While the maintenance requirements and frequency is specific to each facility type, size, and location,
there are some general requirements.The applicant can provide additional maintenance steps however
the following procedures must be incorporated into the facility's O&M Plan.
11.4.1 Catch Basins
Routine cleaning of catch basins is one of the most important methods for protecting water-quality of
waterways and for protecting the infiltration capacity of stormwater facilities. Catch basins must be
cleaned annually or when the sump is reduced by one-third.
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11.4.2 Detention Tanks and Vaults
Maintenance of below-ground Remove oil, sediment, and debris from the facility when it
facilities,such as tanks and exceeds 1/3 of the sump.
vaults,must be completed by In the spring, inspect the vault or tank for structural integrity and
people who have current make the necessary repairs during the summer when the facility
confined space certifications. is empty or mostly empty.
11.4.3 Drywells, Infiltration Trenches, and Infiltration Galleries
If overflows occur during small storms or if water remains for more than 24 hours, check for clogging of
the pipes or perforations. Remove any clogs through vacuum suction rather than jetting to avoid
clogging of the outlying soil and reducing the lifespan of the facility.
UICs and their pretreatment system must be inspected annually for structural integrity.As a general
rule, repairs should be made during the summer when they are relatively empty.
11.4.4 Permeable Pavements and Pervious Pavers
Debris and sediment must be removed from pervious pavement and Sealing pervious pavement
permeable pavers each year.The responsible party can either dry- or permeable pavers is
sweep the area or hire a company that does regenerative air prohibited and a violation
vacuuming.After vacuuming pavers, restore sand or crushed rock of the municipal code.
between the pavers..
If moss prevents infiltration from occurring or creates a public slip hazard, use physical removal
measures. Herbicides and other chemical applications cannot be used for moss removal.
Annually inspect the edge restraints in areas with pavers for structural integrity and repair as necessary.
Over time, settling may occur in areas using permeable pavers. Replace aggregate base, washed sand,
and broken pavers as needed. Refer to manufacturer's recommendations for detailed maintenance
procedures.
11.4.5 Planters, Raingardens, and Swales
Annually inspect pipe inlets and outlets for water tightness and caulk as necessary. For planters check
the structure for concrete spalls or cracks and repair as necessary.
Inspect liners in filtration facilities for structural integrity. Repair holes and tears and close gaps. For
planters, check the metal bar attaching the liner to the concrete and caulk as necessary to maintain a
water-tight connection. Replace attachment bars that have rusted.
For raingardens, ensure that the liner retains at least 6 inches of cover(soil) at the top of the facility.
Remove sediment at the inlets if it exceeds 1 inch or is interfering with plant growth. In areas of erosion,
rake the area level and replace rock and soil as needed to maintain a level surface.
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Vegetation must cover a 100 percent of the surface area of the facility.
The use of herbicides Replace dead or diseased plants. Remove weeds manually and replant
and pesticides to unvegetated areas. Do not use pesticides, herbicides,or fertilizer.
remove weeds in
vegetated facilities
Check for clogging if ponding occurs longer than 24 hours after a storm
isa violation of the event. Clogging can occur in the outlet pipe of a facility or by creating a
municipal code.
layer of sediment on top of the soil. Remove clogs in pipes and rake the soil
to a depth of 4 to 6 inches to regain the infiltration capacity. If no clogs are
present in the pipes and raking is ineffective then replace the soil.
11.4.6 Ponds and Wetlands
Ponds and wetlands must be maintained and inspected annually. Remove sediment that has
accumulated at the inlet, rake to remove rills, and replace rock as necessary. Remove weeds and
replant, as necessary,to maintain 100%vegetative cover of the surface area of the facility. Prune trees
and shrubs as necessary to maintain protect traffic sightlines and pedestrians from plant overhang.
Inspect the interior overflow areas and orifice for structural integrity and repair or replace as necessary.
Remove accumulated sediment.
Inspect the emergency spillway. Remove all trees and shrubs within 20 feet of the spillway. If it is a dirt
or vegetated spillway, rake and replace soil in areas of erosion and repair areas of seepage. If it is a
concrete spillway, check for spalling and cracks and repair as necessary. If repaired areas deteriorate
more than one year, consult a civil engineer (PE)with geotechnical experience for solutions.
Inspect the outlet for clogging if ponding occurs longer than 24 hours for detention and infiltration
ponds. Remove clogs and sediment as necessary. Rake to a depth of 6 inches and replant to achieve 90%
vegetative cover. Sediment in the bottom of the facility, even thin layers, can create areas of dead
vegetation and reduce infiltration.
11.4.7 Sand Filters
The filter medium, including sands and gravels, must allow adequate infiltration.Annually remove
sediment that has accumulated on the surface and check the inlets and outlets for structural integrity.
Remove sediment and debris from structural components. Repair cracks and replace damaged
components as necessary. Rake the sand bed to create a level surface.
Inspect the liner if present. Repair holes and tears and close gaps. Re-attach liner as necessary. Caulk the
liner at the attachment bar and at pipe inlets and outlets to maintain waterproof connections. Replace
the liner attachment bar if it is rusted.
If the facility is vegetated, remove weeds and replant as necessary to retain 100%cover at plant
maturity. Do not use pesticides, herbicides, or fertilizer.
If ponding occurs longer than 24 hours, rake to a depth of 6 inches to restore the infiltration capacity or
replace the soil media. Contact a stormwater engineer if ponding continues to occur beyond 24 hours.
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11.4.8 Vegetated Filter Strips
Filter strips must be inspected annually. Remove accumulated sediment at the inlet and outlet. Evaluate
the vegetation, remove weeds, and replace dead plants to ensure 100 percent coverage. Do not use
herbicide, pesticides, or fertilizer.
Check the inlet and treatment area for erosion. Rake areas where rills have occurred and add rock or
soil, as necessary, to create a level surface. Where flow spreaders are being used, remove sediment and
check for structural integrity. Replace or repair as necessary.
11.4.9 Wetlands
Constructed wetlands must be inspected annually. Remove weeds and replant as necessary. Do not use
herbicides, pesticides, or fertilizer. Check depth and remove accumulated sediment from the interior of
the wetland as necessary to retain the ponding capacity.
Check the overflow for structural integrity and remove accumulated sediment. Ensure that the orifice is
not clogged and is functional; repair or replace as necessary.
Inspect the emergency spillway. Remove all trees and shrubs within 20 feet of the spillway. If it is a dirt
or vegetated spillway, rake and replace soil in areas of erosion and repair areas of seepage. If it is a
concrete spillway, check for spalling and cracks and repair as necessary. If repaired areas deteriorate
more than one year, consult a civil engineer (PE)with geotechnical experience for solutions.
If ponding occurs longer than 24 hours, check the outlet for clogging and remove clogs as necessary.
Sediment in the bottom of the pond, even thin layers,can create areas of dead vegetation and reduce
infiltration. Rake to a depth of 6 inches and replant to achieve 90%vegetative cover.
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12 EROSION AND SEDIMENT CONTROL
Erosion is the movement of soil from land to water or from one area of land to another area. It can be
natural such as beach dunes shifting or the appearance of oxbows in a stream system. It can also be
anthropogenic such as streambank slumping or rills caused by stormwater from development or excess
stream sediment caused by a discharge from a construction site. Because the erosion rate on
construction sites has been estimated to be 500 times greater than on natural sites and because
mercury is naturally present in soil, DEQ has determined that minimizing erosion and stormwater
discharges from construction sites are effective methods for reducing mercury in streams (DEQ, 2019).
Sediment is soil that has been moved by water from one area to another. It can be natural or
anthropogenic such as 1) downcutting in a stream system caused by excessive flows (natural or
anthropogenic) or 2) solids moved by stormwater from impervious or unvegetated areas to waterways.
12.1 REGULATORY OVERVIEW The ESC requirements are
mandated by the Clean
ESCs are implemented at a construction site to ensure that an illicit Water Act and enforced
discharge does not occur at the site. In addition to the SWMM,the by DEQ through the
City's municipal code, MS4 permit, and TMDL Implementation Plan City's NPDES MS4
affect which ESCs are required at a construction site. permit.
12.1.1 Municipal Code
Covered under LOC Chapter 52 of the municipal code,the ESC program requires a permit for any project
that disturbs at least 500 square feet or is within 50 feet of waterways. Landscapers and homeowners
with projects disturbing between 500 and 1,000 sq ft are required to submit a simple ESC plan for
review and approval by the City(see Appendix E for template).
In conjunction with LOC Chapter 52, LOC Article 38.25 prohibits the "discharge, directly or indirectly, of
any pollutant into the surface water management system,private storm drainage system connected
to the surface water management system, or receiving water within city limits. This includes
discharges as a result of an unintentional spill or deliberate dumping."
12.1.2 MS4 Permit
The City's MS4 permit requires that sediment discharges do not occur from construction sites. It
requires staff review of plans, inspections of construction sites, and enforcement. Discharges offsite that
reach the public stormwater system are considered to be illicit discharges and a violation of the
applicant's ESC permit as well as the City's municipal code.
12.1.3 TMDL Implementation Plan
Mercury in sediment accumulates in fish tissue during their life cycle and can become toxic for people
who consume fish. In 2019,the EPA and DEQ revised the mercury TMDL allocation for the City sharply
downwards to combat these issues.
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The City's TMDL Implementation Plan requires source control and ESCs to control sediment movement
and erosion. Steep slopes, riparian areas, and riparian-adjacent projects are required to use coconut coir
blankets to stabilize soil during construction. Non-SFR projects are required to retain a certified ESC
professional to ensure that ESCs remain functional.
12.2 EROSION AND SEDIMENT MOVEMENT
Factors that influence erosion and sediment movement include 1) soil type, 2) slope gradient, 3) slope
length, and 3) project size and timing.
12.2.1 Soil Type
Soil type determines if the ESCs at a construction site should focus on erosion control or sediment
containment. Erosion control is necessary with coarse-grained soil such as loams and sands. Fine-
grained soil such as silt and clays require more focus on sediment controls. A majority of the soil types in
the city are fine-grained, however the west side of the city contains coarse-grained soil because of the
Missoula Floods (see Figure 8—Section 6.2.1).
12.2.2 Slope Gradient
• r- ,`�.� "''y r 4 , Soil particle size affects the stability of slopes.The angle
o- .5 : of repose is a soil property that affects slope stability and
,;: is based on particle size. Beyond the angle of repose, a
0'1 •
slope becomes unstable resulting in slumping. It is very
II� . •` important when grading a construction site, excavating a
trench, or during stream restoration.
As a general rule, doubling the slope increases the
potential for erosion by five times. Unprotected steep
slopes can become unstable during relatively small
storms.
. ' While not intuitive, sites with large excavations or flat
grades can have difficulty with sediment control because
rainfall ponds on the site and,for fine-grained soil, does
not infiltrate easily.A flat site can have difficulty keeping
sediment from being tracked offsite by construction
vehicles. Construction entrances may need refreshing
Steep slopes require additional ESCs
more frequently on a flat site and a project manager may
need to install a tire wash facility to reduce tracking or temporary sediment settling tanks (e.g. Baker
tanks)to reduce sediment in construction stormwater. The same conditions and solutions may be
necessary for a site with a large below-ground excavation such as seen on commercial projects with
underground facilities.
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12.2.3 Slope Length
The slope gradient combined with slope length determines the amount and method of soil movement.
Long steep slopes can result in a landslide however even long gentle slopes can result in rills and gullies.
As the length of a slope increases, stormwater velocity increases and erodes unvegetated areas.As a
general rule, doubling the slope length increases erosion by four times.
12.2.4 Project Size and Timing
Vegetation is the most effective form of erosion control especially for large projects where the work
tends to move from one area to the next and rarely has work occurring everywhere. Breaking a large
construction site into smaller areas of work(phasing) is very effective in reducing disturbed areas and
the likelihood of erosion and sediment movement. Even small projects can benefit from leaving
vegetation in place until clearing is necessary for construction work.
Construction of a project in the summer requires different ESCs than if the project is constructed in the
winter.The dry summers of the Willamette Valley require attention to dust control whereas projects
started in the winter require more sediment control to reduce tracking offsite and the likelihood of a
sediment fence failure. ESC professionals managing sites with large excavations, such as commercial
developments, need to determine if temporary sediment settling tanks or dewatering facilities will be
needed to reduce the volume of ponded water onsite.
12.3 ESC PERMITS
Projects that disturb at least one (1) acre of soil or are part of a common development must apply to
DEQ for a construction stormwater(1200-C) permit. Once approved by DEQ, a copy of the permit, with
the site plan, must be provided to the City's ESC Inspector for review. Unless there are special
circumstances such as riparian areas, land disturbance within 50 ft of a waterway,or steep slopes on a
project, the DEQ-issued 1200-C permit will be accepted for the project.
Applicants must apply for a City ESC permit for all projects that disturb less than an acre and which are
not part of a common plan of development. An online application on the City's website is available for
applicants.
12.3.1 ESC Plans
ESC plans must be submitted as part of the application; they include a narrative as well as a site plan.
The narrative must describe the proposed project and location as well as the ESCs to be used and any
riparian areas or slopes greater than 15%.The site plan sheet(s) must provide the requirements outlined
in Section 4.1.1 (Submittals).
12.3.2 Certified Professionals
Certified ESC professionals are required for non-SFR projects.The City strongly encourages applicants of
SFR or large landscaping projects to engage the services of a certified professional to expedite permit
issuance, decrease time for inspection approvals, and reduce lost time due to enforcement.
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Applicants that use a certified professional can see faster permit approvals and fewer enforcement
actions. Certified ESC professionals know how to create and execute an appropriate ESC plan as well as
how to install, inspect, and maintain the measures.
12.4 EROSION AND SEDIMENT CONTROL SELECTION
The City has adopted Water Environment Services' Erosion
Prevention and Sediment Control Manual for its ESC program. The City has adopted Water
Because the manual is used for urban and rural projects, some Environment Service's Erosion
of the ESCs in the manual are not applicable to the urban Prevention and Sediment Control
environment of the city and could cause a violation of the Manual(available on the City's
City's MS4 permit.Therefore, the decision of certified ESC staff website.
in the Engineering Department is final for plan review and site Questions and inquiries about the
inspections. Erosion Control Program can be
answered by contacting the City's
12.4.1 Required Erosion and Sediment Controls Erosion Control Inspector.
Every project must provide a construction entrance, catch
basin inserts, proper waste management including
covered/closed dumpsters, sediment fences around the project perimeter, and wattles near tree
protection areas.A leak-proof concrete wash-out is required to be onsite before the foundation pour
and during all activities that involve the use of cementitious materials such as grout, mortar, concrete,
or stucco.All projects adjacent to Oswego Lake or its canals must provide silt curtains.
12.4.2 Construction Access and Parking
As the primary access point for construction,the
construction entrance must be installed before any work is ":i.: a
done including clearing and grubbing(see Standard Detail - .
E1-06). Using rock with fines or not properly refreshing the t = �
t
rock during construction can result in sediment leaving the ,$ ;
construction site with subsequent citations and other - r `' '
enforcement actions.
Construction site parking is a common source of land •
disturbance and tracking. Keep parking limited to hard- Interlocking pathway on lakebed
surfaced or compacted graveled areas. Do not block the
construction entrance with crew parking,job trailers, or materials.
Load and unload materials within the construction site perimeter and not from the street. Even small
equipment can cause serious land disturbance or tracking from the site. Material spills or waste
discarded outside the construction site perimeter can result in a stop work order, citations, fines or a
combination of these actions.
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12.4.2.1 Maintenance
The function of a construction entrance is to minimize the amount
Washing dirt or debris into of sediment leaving a site. It also provides a focused access for
the street, curb inlets, or vehicles to enter and leave a site.
catch basins is a violation of •Keep construction entrances of dirt and debris. Refresh rock as it
the ESC permit and municipal becomes filled with soil from the site.
code.
•Sweep streets adjacent to the construction site at the end of
each day.
12.4.2.2 Optional Controls
For smaller projects with limited access, a construction pathway can be used instead of a construction
entrance.The pathway must use plywood or steel sheeting to reduce land disturbance and limit damage
to existing root systems. For larger projects or larger equipment near water bodies, interlocking
pathway boards capable of withstanding 600 psi can be used to minimize sediment tracking.
A tire wash facility may be necessary for large sites or projects where the construction entrance has
been shown to be ineffective in eliminating tracking offsite.
12.4.3 Sediment Control
The function of a sediment control is to prevent sediment from leaving a site. It detains stormwater and
allows fine-grained particles to settle out.
Required sediment controls include sediment fences, catch basin inserts, wattles near tree protection
areas, and silt curtains for projects adjacent to Oswego Lake.
12.4.3.1 Sediment Fences (Detail E-03)
Sediment fences are required at the limits of clearing for all ��*..� 9 y—, :; ;
projects. If construction fencing is not used at the site, iff
sediment fences must be used to protect and delineate
sensitive lands, placed around the perimeter of stormwater
facility locations, and installed at the project limits.
On slopes,the fence must be at a set elevation (across the
slope), rather than sloping (following the descent of the
property),to avoid channelized runoff and fence failure.
3.�
Multiple lines of sediment fence may be necessary on long or
steep slopes to avoid failure of the fence during storm events. Joining sediment fence segments
Sediment fence must be trenched in to a depth of six inches (usually denoted by a line on the sediment
fence) and staked.The fence must be straight and not sag. Lengths of sediment fence are joined
together by wrapping two end stakes together at least 2 times.
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12.4.3.2 Catch Basin Inserts (E1-01)
Catch basin inserts are required to protect all catch basins within 200 feet of the project perimeter.They
are a final effort to avoid a sediment discharge into the stormwater system.They are NOT a primary line
of defense.
12.4.3.3 Wattles
Wattles are required at tree protection areas and can be used as secondary protection on the site.They
must be installed between the tree protection fence and the disturbed area and staked down.Wattles
cannot be used as a primary ESC anywhere other than tree protection areas.
12.4.3.4 Maintenance
Sediment must be removed from sediment fences when it reaches 1/3 of the height of the fence.The
weight of water ponding next to a sediment fence will break the wooden stakes of the fence, allow an
uncontrolled discharge from the site, and result in a violation of the ESC permit. If sediment hasn't been
removed from a fence, it can exacerbate the situation because the water's weight will be centered
higher on the fence line.
Stakes in a fence must be replaced when they are broken and fence sections must be replaced when a
hole develops in the fence material.
Catch basin inserts must be replaced when they become 1/3 filled with sediment.
Wattles must be replaced when they become flattened or filled with sediment. Driving over them will
increase replacement frequency.
Sediment removed from sediment control measures can be distributed back on flat areas of the site
after dewatering.A 50-ft vegetated buffer must separate riparian areas and stormwater facility locations
from areas where sediment is re-distributed.
12.4.3.5 Optional Controls
Buffer zones may be used to prevent run-on and to protect riparian areas. Preserving natural vegetation
reduces the amount of soil disturbed during at one time on a construction site. It can be used to phase
construction of large projects or as a sediment control for small projects.
Biobags or dewatering bags may be used to filter stormwater.They can be used to provide additional
protection for the required sediment fences and catch basin inserts but cannot be used to replace them.
Biobags must be replaced when flattened or filled with sediment. Dewatering bags must be replaced
when they become clogged or when turbid water is leaving the bag.
If additional sediment removal or additional time for removal is needed then temporary sediment
settling tanks can be used to provide the time necessary to remove sediment. If chemicals are needed to
enhance sediment removal, pH monitoring is required to keep the pH between 6.5 and 8.5 before
stormwater is discharged offsite.
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12.4.4 Run-on Control
While sediment control is the primary ESC used in the city, project managers should minimize the
amount of water entering the site from adjacent properties. Channelized stormwater or groundwater
should be diverted from exposed soil or steep slopes to reduce erosion and sediment transport.
Water from adjacent properties should be diverted from unvegetated areas on a site and routed to the
downslope side of the property for discharge off the site. If it is allowed to reach unvegetated areas,the
project will require additional sediment controls to filter the water before it is discharged offsite.
Swales and pipe slope drains can be used to divert water aware from disturbed areas. Both will require
an outfall at the perimeter of the site to reduce velocity and prevent erosion at the discharge point.
Swales on slopes will require check dams to reduce water velocity and trap sediment.
12.4.4.1 Maintenance
Remove sediment and regrade below outfalls to repair erosion. Placing a geotextile or coconut coir
blanket below the rock used for the outfall will reduce scour and maintenance time.
12.4.5 Dust Control
Dust from a construction site must be minimized during dry weather. Using water trucks to wet
disturbed soil is the required method for dust control in the city. Other approved methods for
minimizing dust include seeding, mulching, or using coconut coir blankets.
12.4.6 Stabilize Slopes and Disturbed Areas
Unvegetated areas and slopes are a source of sediment during storm events. Areas that have been
cleared, but are not under active construction, must be stabilized until active construction. If the soil will
be exposed during winter, it must be covered at the end of each day.
Cover unvegetated areas with 3 inches of straw, compost mulch,wood chips, gravel, or other ground
cover to minimize land disturbance and reduce the potential for tracking. Coconut coir blankets are
required for all projects with slopes 15%or greater(see Detail E1-04) and for all areas that are 50 feet
(measured horizontally) or closer to a waterway (See Detail E1-05).
12.4.6.1 Maintenance
Replace or add more ground cover when patches of bare soil can be seen. Repair holes in coconut coir
blankets or replace them if the holes are too large to adequately repair.
12.4.6.2 Optional Controls
Surface roughening, or tracking, can be used to prevent erosion of a slope. Ensure that equipment tracks
up and down the slope, instead of cross-slope,to prevent forming channels on the slope.
Pipe slope drains can be used to divert water from disturbed sloped areas but are not a substitute for
stabilizing the soil.
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Permanent or temporary seeding may be used to stabilize soil. Hydroseeding or using a bonded-fiber
matrix is the easiest method for large sloped areas or stockpiles that need to be stabilized.
Plastic sheets can be used but must be surrounded by sediment fence when used on a slope or to cover
a stockpile. Rain falling on a plastic sheet will create runoff on the construction site. It should be
diverted before reaching unvegetated areas to reduce erosion and sediment movement on a site.
12.4.7 Stockpile Areas
Material storage areas must be identified on the ESC plan. Materials, other than soil, must be placed on
a hard surface such as a gravel base, or plywood. Soil stockpiles must be encircled by a sediment control
such as a sediment fence. When plastic sheeting is used,tie-downs or anchors are required to keep the
plastic from becoming airborne (see Detail E1-07). A dual barrier is recommended for large stockpiles.
Soil stockpiles must be covered daily during active construction.They must be covered or hydroseeded if
unworked for 14 days or longer.
12.4.7.1 Maintenance
Repair holes in sheeting and maintain equidistant spacing of tie-downs/weights. Replace sheeting if
holes are not able to be adequately repaired. Remove material from behind barriers when it reaches 1/3
of the height of the barrier.
12.4.7.2 Optional Controls
Stockpiles of compost, bark dust, topsoil, or other amendments may be placed on tarps if the storage
time onsite is minimized,the volume is minimal, and methods are installed to divert water or control
discharge from the stockpile.
12.4.8 Source Control
Project managers must minimize, store, control, and dispose of construction waste properly. Closed
trash containers, spill response kits, and concrete washout containers are required for every project.
Construction waste must be stored away from stormwater facilities and waterways.
All concrete wash-out, mortar, grout, wet saw ,
slurry, and other liquid wastes must be
contained in leak-proof prefabricated pans. '"
Onsite construction of washout containers is
prohibited. y .
Ground or open-pit dumping is prohibited.
Additional requirements may be required by
t.
the City's certified ESC professionals.
12.4.8.1 Maintenance
Leak-proof concrete washout containers must be removed after a concrete pour is completed or when
they become 2/3 full including washwater and rainfall.
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Trash leaving a site is a violation of the ESC permit. Construction
sites must be cleaned of outdoor trash at the end of each day or Source control includes:
immediately when strong wind gusts are forecast.Trash must be • Storage of solid waste
placed in leak-proof covered containers that are marked as including concrete waste.
"Trash". Small (up to 55-gallon) containers must be emptied • Spill prevention and
weekly or when %full.They can be emptied into larger response.
containers. Larger containers such as drop-off bins must be • Disposal of fluids and
emptied monthly or more frequently if needed.
wastes.
Discarded building materials should be sorted by recyclability • Control of emissions from
such as steel and wood.They must be stored in closed recycling painting,finishing, and
containers. coating of buildings and
Spill response kits must be located in easily-accessible areas and equipment.
have prominent signage. Kit materials must be replenished as • Storage or transfer of solid
soon as possible after they are used so that the kit has its materials, by-products, or
maximum spill response capability. Staff must be properly trained finished products.
in spill response with documentation of the training available to
City staff upon request.
12.4.9 Wet Weather Requirements
ESC requirements for the wet weather season (October 1st to May 31st ) are in addition to standard ESC
requirements and must be included, or incorporated by reference, into the ESC plan.
• All stockpiled material must be fully covered with secured plastic sheeting and isolated with silt
fencing or check dams/wattles at the toe of the slope unless being actively accessed.
• All unvegetated areas must be covered at the end of each work day with a 3-inch minimum
depth of straw, compost mulch, or wood chips.
• Inspections are increased to weekly and within 24 hours of storm events exceeding 0.5 inches
of precipitation within 24 hours.
12.5 PRE-CONSTRUCTION
ESC effectiveness is increased with good project management.These practices include efficient
scheduling, project phasing, awareness of weather conditions, and training.
12.5.1 Schedules and Phasing
Scheduling can be a very effective means of reducing construction impacts. Reducing the number of
contractors onsite reduces the amount of parking needed, the likelihood of tracking sediment offsite,
the likelihood of accidental spills, and the amount of waste to manage at the site.
Phasing, when used, must be communicated to Engineering Development Review staff during plan
review with each phase and its ESCs documented on a separate plan sheet.
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12.5.2 Weather Forecasts
Weather forecasts including expected precipitation amounts are available
Project managers from the National Weather Service (www.weather.gov) or local weather
must be aware of forecasting websites. Hourly precipitation forecasts are available at these
changing weather websites in addition to radar. Some local websites include forecasts by
conditions at all the minute for 2-hr windows. Using the City's two primary zip codes of
times. Not being 97034 (east side) and 97035 (west side) can result in more precise
aware of a wind or weather forecasts.
precipitation event
is not a defense Activities should be scheduled, as much as possible, based on the season
against an ESC and daily weather forecast. For example, grading activities should occur
violation. during dry periods and disturbed areas must be stabilized if rain is
forecast within 24 hours.
Soil stockpiles must be covered and sediment fences must be inspected to ensure that they are in good
condition and will be able to withstand the amount of runoff expected from a storm. Catch basin inserts
must be inspected and replaced if sediment is near the 1/3 depth required for replacement in order to
reduce flooding and failure of the insert during a storm.
12.5.3 Training
Staff and subcontractor training on ESC requirements is required for all projects. If construction
practices result in an ESC violation,the permittee will pay any fines associated with the violation even if
it was caused by a subcontractor. Stop work orders apply to the entire site.
12.6 CONSTRUCTION
After the ESC application is approved and the permit is issued, the applicant must install the
construction entrance before installing the other approved ESCs because of the likelihood of equipment
tracking soil offsite after unloading materials. After the site has been protected by the ESCs,the
applicant must schedule the initial inspection and obtain approval from the City ESC inspector before
clearing and grubbing.
Clearing and grubbing before approval of the 1"ESC inspection is a
violation of the ESC permit.
Establishing protective buffers and minimizing grading at the beginning of a project and around sensitive
lands, such as riparian areas and stormwater facilities,will reduce the chance of an ESC or sensitive
lands violation.
Minimizing the extent and duration of exposed soils and maximizing the preservation and protection of
site features, especially areas to be used for stormwater management, will reduce potential erosion and
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sedimentation. Compaction of areas used for infiltrating stormwater can lead to failure and subsequent
reconstruction of the facility before approval of the final ESC inspection.
12.6.1 Inspections and Inspection Logs
Approval of an ESC
City ESC staff will routinely visit project sites to ensure that the approved plan by the City does
ESCs are properly installed and functional. While three inspections are not relieve the
mandatory and must be scheduled with the City's ESC Inspector, permit holder from
construction sites that are active for more than 6 months may receive the responsibility to
additional inspections. ensure that ESCs are
properly installed
ESC inspectors hired by the applicant or contractor must be, at a minimum, and maintained at
knowledgeable in ESC maintenance. Inspectors for subdivisions or on the construction site.
properties zoned as commercial, industrial, or multi-family must possess
certification as an ESC professional.
Inspections should occur on a routine basis and before large storm events.All ESC inspections at the
construction site must be documented during the project.The inspections must be recorded in an
inspection log documenting 1) the date of the inspection, 2)the amount of rainfall during and 24-hours
prior to the inspection, 3)the type and location of the inspected ESCs,4) observed issues and any
corrective actions taken, and 5)the inspector's name and signature. Inspections must be documented
with photographs and any sampling results.
The inspection log must be kept onsite at all times and available to City or DEQ inspectors upon request.
Four weather stations, located in various areas, are maintained by the City and can provide information
on the amount of precipitation required for the inspection logs.The weather station location and the
collected information is available at the water conservation page on the City's website.
12.6.2 Significant Discharges
The following discharges from a construction site are considered significant. !
They must be included on the permittee's inspection log and documented d 1.
with photographs: � y
•Earth slides or mud flows.
•Evidence of concentrated flows such as the presence of rills, channels, or
gullies. r.
•Turbid water leaving the construction site. x
•Sediment from the construction site tracked onto public or private streets. ,k
*Sediment on adjacent property that is not part of the project. �sy �
When a discharge occurs,the ESC permittee is responsible for informing the A significant discharge
City's ESC Inspector, updating the ESC plan to prevent another occurrence,
and submitting the modified plan to the City's ESC Inspector for review and approval. Unreported
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discharges discovered during a City inspection are a violation of the ESC permit and subject to citations,
fines, stop work orders, and permit revocation.
12.6.3 Modifications to Approved ESC Plans
It is important to modify the ESC Plan to respond to changing conditions at the
Ineffective ESC construction site. Additional controls must be installed immediately if site
Plans are subject conditions deteriorate because of rain or ineffective controls.A modified ESC
to fines and Plan documenting these changes must be sent within 2 business days to the
enforcement. City ESC Inspector for review and approval.
Changes not needed to respond to a time-sensitive event must be documented
as a modification on the previously-approved ESC plan and sent to the City's
ESC Inspector for approval prior to making the change in the field.
12.6.4 Enforcement
To avoid a citation, contractors and developers must inspect and maintain all ESCs on a regular basis.
Stop work orders, citations, fines, and permit revocation may be issued for failure to install and maintain
required ESCs, or for allowing sediment or other pollutants to enter waterways or the public stormwater
system.
Stop work orders apply to the entire construction site.
12.6.5 Post Construction
After a project has been completed, the disturbed area must be stabilized using permanent landscaping
material. When the disturbed area has been stabilized, the ESCs may be removed from the site and from
adjacent catch basins. For developments with multiple buildings or structures, ESCs must remain until
the last building or structure has been completed and all disturbed soil is stabilized.
Mulched areas larger than 100 sq ft which have no other stabilization
method will not be considered to be stabilized.
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13 DEFINITIONS
303(d) list
A list developed in conformance with Section 303(d) of the federal Clean Water Act that identifies
waters that do not meet water quality standards and where a total maximum daily load (TMDL) needs to
be developed.
Access Road
The area on private property that extends from the public ROW and is used to access and maintain a
stormwater facility.
Aggregate
Rock of specified quality and gradation.
Aggregate, Fine
Crushed rock, crushed gravel, or sand that passes a 1/4" sieve.
Altered
Changed from the City's original approved design.
Applicant
An individual, group, or legal entity that submits documents to the City Engineer for review and
approval.
Approval
For the purposes of this Manual, approval is the written notice that Engineering staff have reviewed and
approved the documents submitted in compliance with stormwater requirements.
As-Built
Drawings showing the constructed surface and subsurface utility infrastructure and their surveyed
locations on the vertical and horizontal plane.
Base Course
A layer of material placed under the surface wearing course of a pavement and its bedding course in
order to support them. For permeable pavements,the base course is open-graded.
Bankfull
Elevation at the lower edge of perennial vegetation in the riparian corridor. It is the depth reached in a
waterway during the 1.2-yr 24-hr storm event.
Base Flood
The flood having a one percent chance of being equaled or exceeded in any given year. For areas
influenced by the Willamette River, it is the elevation reached during the 1996 flood. Reference LO Maps
and LOC Figure 50.05.011-A, Maps A to D.
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Base Flood Elevation
The elevation to which floodwater is anticipated to rise during the base flood, as determined by FEMA,
plus a safety factor of 2.7 feet. For areas influenced by the Willamette River, it is the elevation reached
during the 1996 flood plus 2.7 feet.
Bedrock
The native, contiguous, consolidated rock underlying the surface of the Earth. Above bedrock is usually
an area of broken and weathered unconsolidated rock or soil. Bedrock is sometimes exposed on the
surface, indicating that soil has been eroded.
Beneficial Use
The purpose or benefit to be derived from a waterway as designated by the Oregon Water Resources
Department or the Oregon Water Resources Commission.
Bridge
A single or multiple span structure, including supports, that carries motorized and non-motorized
vehicles, pedestrians, or utilities on a roadway,walk, or track over a watercourse, highway, railroad or
other feature.
Built-out
Land developed to the maximum extent allowed by the Comprehensive Plan's zoning designations.
Capacity
The flow volume that a conveyance structure is designed to transport. See also design capacity.
Catch Basin
Structure with a sumped sediment storage below an outlet pipe that collects and conveys stormwater to
a stormline or a stormwater facility.
Channel
The land features (bed and banks) that confine a stream.
Channelized Flow
Stormwater flow that generally occurs 300 feet from the point of origin along the flow path but which is
not in an open channel.
Check Dam
A rock structure placed across an open channel or stormwater facility to control water depth or velocity.
Choker Course
A layer of aggregate placed into a facility to provide stability and reduce finer material above it from
migrating to the coarser layer below it.
Civil Engineer
An engineer, recognized by OSBEELS as a licensed professional, with experience in stormwater
hydraulics and/or hydrology.
Cleanout
An access port, less than 6 inches in diameter, used to clean or inspect underground pipes or structures.
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Clearing
Activity that removes vegetative cover while leaving the root system intact.
Construction
Includes, but is not limited to, clearing, grading, excavation, and other site preparation or ground-
disturbing work related to the construction of residential buildings and non-residential buildings, and
heavy construction (e.g. highways, streets, bridges, tunnels, pipelines,transmission lines, and industrial
non-building structures).
Contaminated Soil
Soil which does not meet the Oregon Department of Environmental Quality's Clean Fill Determinations.
Contractor
The person, partnership,firm or corporation licensed in Oregon contracting to complete construction.
The term shall also include the Contractor's agents, employees and subcontractors.
Contour
The vertical location of the ground surface as depicted by a line drawing.
Conveyance System
A system of structures to detain and convey stormwater in a manner that allows efficient flow to a
discharge point.
Course
A material placed in one or more lifts to a specified thickness.
Cross-Section
The image formed by a plane cutting through an object, at right angles,to a central axis. Generally used
for conveyance structures and stormwater facilities.
Crown
The inside top of a pipe.
Culvert
A conduit, open on both ends,that conveys water under a road, driveway or embankment in order to
connects two stream segments or open channels.
Curve Number(CN)
A factor used in hydrologic models using the SCS runoff equation, such as TR-55 and the Santa Barbara
Urban Hydrograph,that is a function of the soil type, antecedent moisture, land cover, and infiltration
capacity, and land use.
Designated Management Agency(DMA)
A federal, state or local governmental agency that has legal authority of a sector or source contributing
pollutants, and is identified as such by the Department of Environmental Quality in a TMDL" (OAR 340-
042-0030(2)).
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Design Capacity
The flow volume or rate that a stormwater facility or structure is designed to contain, treat, detain, or
conveyor infiltrate to meet a specific performance standard.
Design Flood Elevation
One foot above the base flood elevation.
Design Storm
A storm event with a specific amount of precipitation in a specified amount of time which is used to
design stormwater infrastructure.
Detention
The storage and controlled release of stormwater during and after a storm event.
Development
Any manmade change to unimproved real property, including, but not limited to, construction,
installation or alteration of a building or other structure, change of use, land division, establishment or
termination of a right of access, storage on the land, grading, clearing, removal or placement of soil,
paving, dredging,filling, excavation, drilling or removal of trees.
Discharge
The volume of water or stormwater moving from one point to another over a specific time period, e.g.
cubic feet per second (cfs).
Discharge point
The location at which water or stormwater leaves a watershed or structure.
Ditch
A constructed open linear depression which conveys stormwater and where infiltration is incidental.
Easement
The area of land granted for use by the City for the construction, reconstruction, operation,
maintenance, inspection and repair of utilities.
Edge Restraint
An edging or curb that surrounds the bedding course of pavers to that they do not move laterally under
loading.
Emergency
An event or circumstance causing or threatening life, injury to persons or property, and includes, but is
not limited to,fire, explosion,flood , severe weather, multi-year drought, earthquake,volcanic activity,
spills or releases of oil or hazardous material, contamination, multi-day utility or transportation
disruptions, and disease.
Engineering Development Review Staff
City staff with responsibilities for stormwater management. For capital improvement projects (CIPs), it
means the CIP Project Manager.
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Energy Dissipation
The use of rock or concrete to reduce stormwater velocity.
Erosion
The process of wearing of soil by water, wind, ice, or gravity and the detachment and movement of soil
particles by the same methods.
Establishment Period
The time to ensure satisfactory establishment and growth of planted materials.
Excavation
Any act by which soil or rock is cut into, dug, quarried, uncovered, removed, displaced or relocated.
Existing
Buildings, facilities or conditions, which are already in existence, constructed or officially authorized.
Facultative
Vegetation that can occur in wetlands and uplands.
Fill
Placement of any soil, sand, gravel, clay, mud, debris, refuse, or any other material, organic or inorganic.
Filtration
The treatment of stormwater using vegetation, sand or media designed to specifically remove a
pollutant but which does not include infiltration.
Fine Aggregate
See Aggregate, Fine.
Flatwork
Flatwork includes, but is not limited by, sport courts, covered decks, outdoor kitchens, spas and pools
with associated decking, hardscaping, driveways, sidewalks, patios, and parking lots.
Floodplain
The land subject to a periodic flooding from a waterway.
Flow Control
The controlled release of stormwater used to reduce post-development flowrates to pre-development
flowrates.
Flow-Through
See Filtration.
Freeboard
The vertical distance from the top of the ponding depth to the point at which water overflows a
structure or enters an overflow structure.
Grading
Altering the contour,topography, or natural cover of the land.
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Gravel
Particles of rock, rounded or not,that will pass a 3-inch sieve and be retained on a No.4 sieve.
Green Infrastructure
Stormwater infrastructure that 1) uses vegetation or other pervious surfaces to treat or infiltrate
stormwater or 2) allows the storage of rainwater for later use. See also Low Impact Development.
Groundwater
Subsurface water that occurs in the saturated zone of a geological formation and which fluctuates
seasonally. Seasonally high groundwater,for the purposes of calculating separation distance to
stormwater facilities, includes perched groundwater.
Hardscaping
Landscaping that provides structure and functionality to outdoor areas but which results in an impervious
surface. It includes, but is not limited to, water features, fire pits, retaining walls, covered arbors and
gazebos, and playgrounds not using woodchips or lawn as a surface.
Hazardous
A material or waste that exhibits one or more of the following characteristics: toxic, corrosive, irritant,
strong sensitizer, flammable, combustible, or pressure-generating through decomposition, heat or other
means.
Hydraulics
The study of the conveyance capacity of a stream or stormwater system given a specified amount of
water at a given time.
Hydraulically-restrictive soil layer
Bedrock,glacially consolidated soils with more than 50%fines, or glacially unconsolidated soil with more
than 70%fines.
Hydrograph
A graphic display of the discharge of stormwater over time.The area under the hydrograph represents
the total volume of stormwater created during a storm.
Hydrologist, Professional
A hydrologist, recognized by the American Institute of Hydrology as a certified professional,with
experience in hydrology and hydraulic analysis.
Hydrology
The study of water as it occurs in the atmosphere, on the surface or underground.
Hydromodification
Modification of a stream channel due to urban development that either directly or indirectly results in
elevated streamflow and peak velocities over undeveloped conditions.
Impervious Surface
A manmade surface that prevents or retards the entry of water into the underlying soil. Non-traditional
surfaces include but are limited to: artificial turf, building eaves;walkways; compacted gravel areas;
pools;flatwork, hardscaping, and packed earthen materials.
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Impervious Area
See Impervious Surface.
Infiltration
The movement of water through the soil matrix. See also Surface Infiltration.
Inlet
A structure used to convey stormwater into a stormwater facility or into a stormline.
Inspector
City Engineering representative authorized to inspect and report on project performance.
Invasive Plant
A non-native plant that causes economic or environmental harm and is capable of spreading to new
areas of the State (ORS 570.750).
Invert elevation
The elevation of the lowest part of the inside of a pipe, culvert, or ditch.
Land disturbance
Any activity that alters the land surface in a way that modifies its characteristics and that affects it
potential for runoff or erosion.
Landscaping
An activity that modifies the physical features of an area of land
Large Project
A project that 1) creates, 2) replaces, or 3) creates and replaces a total of 3,000 square feet or more of
effective impervious area.
LO Maps
The City's GIS map of contours, watersheds, waterways, and utilities (wastewater, water, and
stormwater) among other layers.
Low Impact Development
A stormwater management approach that seeks to mitigate the impacts of increased runoff and
pollution using a set of planning, design, and construction approaches that promote the use of natural
systems for infiltration, evapotranspiration, and reuse of rainwater.
Microclimate
A local climate that is different from the overall climate of an area and has, among other characteristics,
1) temperatures affected by large impervious areas, adjacent concrete or brick, 2) shading from tall
buildings or large tree canopies, or 3)wind affected by traffic or tall buildings.
Middle Housing
Duplexes,triplexes, quadplexes, cottage clusters, and townhouses in residential zones.
Municipal separate storm sewer system (MS4)
As defined by 40 CFR 122.26(b)(8), "a conveyance or system of conveyances(including roads with
drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm
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drains): (i) Owned or operated by a state, city,town, borough, county, parish, district, association, or
other public body(created to or pursuant to state law) including special districts under state law such as
a sewer district,flood control district or drainage district, or similar entity, or an Indian tribe or an
authorized Indian tribal organization, or a designated and approved management agency under section
208 of the Clean Water Act that discharges into waters of the United States. (ii) Designed or used for
collecting or conveying stormwater; (iii)Which is not a combined sewer; and (iv)Which is not part of a
Publicly Owned Treatment Works (POTW) as defined at 40 CFR 122.2."
National Pollutant Discharge Elimination System (NPDES)
A program initiated by the U.S. Congress in 1972 and amended in 1987 as part of the Clean Water Act
that regulates stormwater discharges into navigable or regulated waters.
Naturalized Plant
A non-native plant that co-exists with native plants but does not cause environmental or economic
harm.
Noxious Weed
An invasive plant that is a priority of the Oregon Noxious Weed Control Program for prevention and
control due to its economic or environmental impact.They are not easily controlled with chemical,
biological, or physical methods.
Open channel
A structure used to convey channelized water that is partially or fully exposed to the atmosphere.
Operations and Maintenance
Activities required to keep stormwater assets and their components functioning in accordance with their
design objectives. It does not include repairs to a failed or failing structure or repairs required to avert
an emergency situation.
Operations and Maintenance (O&M) Plan
A plan which describes the maintenance required, for a stormwater system and its components
as well as a description of the system's operation.
Orifice
A structure used to control the flowrate out of a stormwater facility or conveyance structure.
Outfall
A structure used to discharge stormwater to a receiving water.
Overflow elevation
The elevation at which water flows into the overflow or outlet of a facility.
Peak flowrate
The maximum rate of flow during or after a precipitation event.
Permeable interlocking concrete pavement(PICP)
Concrete pavers placed in an interlocking pattern with aggregate (not sand) used to fill in the joints
between the pavers.
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Pervious
A surface that is able to infiltrate precipitation.
Planter
A vegetated stormwater facility with vertical walls composed of structural concrete.
Pollutant
Pollutant means dredged spoil, solid waste, incinerator residue,filter backwash, sewage,garbage,
sewage sludge, munitions, chemical wastes, biological materials, concrete wash water, paint, radioactive
materials (except those regulated under the Atomic Energy Act of 1954, as amended [42 U.S.C. 2011 et
seq.]), heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and
agricultural waste discharged into water.
Ponding Depth
The depth of water allowed in a facility before stormwater enters the overflow structure.
Pre-development
Conditions expected to have been present prior to development or land alteration by Anglo-Europeans
(i.e. conditions present at the time of the Lewis and Clark expedition) and represented by a curve
number of 70.
Pretreatment
Treatment of stormwater to remove a specific pollutant prior to being discharged to a stormwater
facility or the public stormwater system.
Professional Engineer
A civil engineer licensed by OSBEELS. See also Civil Engineer.
Public Improvement
An improvement to the public infrastructure required as a condition of private development and built by
a private entity.
Raingarden
A vegetated stormwater facility with a level bottom, sloped sides, and a length under 100 ft.
Receiving water
The waterway receiving stormwater from a public or private stormwater system.Virtually all receiving
waters are Waters of the State, and include "lakes, bays, ponds, impounding reservoirs, springs, wells,
rivers, streams, creeks, estuaries, marshes, inlets, canals,the Pacific Ocean within the territorial limits of
the State of Oregon, and all other bodies of surface or underground waters, natural or artificial, inland
or coastal, fresh or salt, public or private (except those private waters that do not combine or effect a
junction with natural surface or underground waters)that are located wholly or partially within or
bordering the state or within its jurisdiction." (ORS 4686.005(10)).
Redevelopment
The removal of impervious area on a property combined with construction of impervious area that may
or may not coincide with the original impervious area footprint. Construction may or may not be
completed at the same time as the impervious area removal.
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Regional Facility
A stormwater facility receiving stormwater from multiple properties and which provides detention. For
the purposes of design, a regional facility includes constructed wetlands, retention ponds, detention
ponds, and infiltration ponds.
Renovation
(a) Structural repair or alteration of a failing or failed stormwater facility that is not stormwater facility
maintenance. (b) Nonstructural repair or alteration of a failed stormwater facility that is not stormwater
facility maintenance.
Replace or replacement
The removal of an impervious surface that exposes soil followed by the placement of an impervious
surface. Replacement also means the construction of a stormwater facility to substitute for an existing
stormwater facility. It does not include repair or maintenance activities on failing or failed structures or
facilities.
Restoration
Nonstructural repair or alteration of a failing stormwater facility that is not stormwater facility
maintenance.
Retention
The process of collecting and holding stormwater with no outflow.
Right-of-Way(ROW)
Public land used for public roads and utilities.
Rill
Small channels created by stormwater that are only a few inches deep
Santa Barbara Urban Hydrograph (SBUH)
A hydrologic model that converts the runoff from a design storm into a hydrograph and routes it
through an imaginary reservoir.
Sedimentation
Deposition of sediment.
Seasonally High Groundwater
See Groundwater.
Sensitive lands
Areas that the City has designated as sensitive and that have environmental significance such as
wetlands, stream corridors, and tree groves, and that are more sensitive or easily damaged by
development impacts than non-sensitive land.
Single-Family Residential (SFR)
Projects completed on properties zoned as low or medium density residential and that are not
considered as middle housing.
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Sheetflow
Laminar flow that is not channelized and generally occurs from the point of origin to 300 feet along the
flow path.
Small Project
A new or redevelopment project that creates 1,000 sq ft of impervious area but less than 3,000 sq ft.
Source Control
A structure or operation intended to prevent pollutants from coming into contact with stormwater
through physical separation of areas.
Spall, Concrete
The weathering or deterioration of concrete resulting in pieces breaking off from the main structure.
Spillway
An outlet used to pass flows exceeding a pond or wetland's design capacity.
Standard Details
The set of detail drawings contained in the City of Lake Oswego's "Standard Construction Specifications
and Drawings."
Steep slope
Topography with a slope of 15 percent or more.
Storm Drain
A structure that receives stormwater from a street and conveys it to a stormline.
Stormwater
Water from precipitation, primarily rainfall and snowmelt,that runs off impervious surfaces.
Stormwater facility
Designed facilities intended to treat, infiltrate, detain, or convey stormwater.
Stream
A naturally flowing surface water that produces a definable channel and which can be perennial,
intermittent, or ephemeral. It includes areas where development was allowed to divert the natural
stream channel but does not include ditches, swales, or overflow channels from stormwater facilities.
Sump
The distance from the bottom of the structure to the bottom of the outlet pipe.
Surface Infiltration
As defined by OAR 340-044-0005, surface infiltration is defined as fluid movement from the ground
surface into the underlying soil material. See also Infiltration.
Surface water management system
The natural and manmade facilities utilized by the surface water management utility to regulate the
quantity and quality of surface water, including drainage easements, stormwater conveyance and
treatment facilities, and waterways.
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Surface water management utility
The surface water management utility is the entity that plans, designs, constructs, maintains,
administers, and operates all City surface water conveyances and facilities, and the regulations for
facility control.The surface water management utility also establishes standards for design and
construction.
Swale
A linear vegetated facility with sloped sides, check dams, and a length of 100 feet or more.They differ
from ditches in the reduced velocity and gently sloped sides.
Time of Concentration
The time required for stormwater to travel from the most hydraulically-distant point in an area of
interest to the discharge point.
Total Maximum Daily Load (TMDL)
the amount of an identified pollutant, as determined by DEQ, that a specified waterway can receive and
still meet water quality standards.
Underground Injection Control
Discharging stormwater into the underlying soil material without allowing surface infiltration. For the
purposes of stormwater design, UIC facilities approved for stormwater management include infiltration
trenches, infiltration galleries, and drywells.
Utility
The public wastewater, water, and stormwater systems used to provide City services.
Vegetated Facility
A stormwater facility that uses vegetation and a specific soil mixture to treat stormwater. Vegetated
facilities include raingardens, planters, swales, and vegetated filter strips.
Waters of the State
Lakes, bays, ponds, impounding reservoirs, streams, creeks, estuaries, marshes, inlets, canals,the Pacific
Ocean within the territorial limits of the state of Oregon, and all other bodies of surface or underground
waters, natural or artificial, inland or coastal, fresh or salt, public or private (except those private waters
that do not combine or effect a junction with natural surface or underground waters)that are wholly or
partially within or bordering the state or within its jurisdiction [OAR 340-045-0010].
Waterway
Waters of the State as well as springs, wells, rivers, and all other bodies of surface or underground
waters,that are located wholly or partially within the City or for which it has jurisdictional authority.
Wearing Course
The top surface of a pavement system which is directly subject to traffic loads.
Wetland
An area that is inundated or saturated by surface water or groundwater at a frequency and duration
sufficient to support, and that under normal circumstances does support, a prevalence of vegetation
typically adapted for life in saturated soil conditions, commonly known as hydrophytic vegetation.
Wetlands generally include, but are not limited to, swamps, marshes, bogs and similar areas.
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14 REFERENCES
American Concrete Institute (ACI),June 2023, Pervious Concrete—Report, ACI PRC—522-23.
American Public Works Association (APWA) and Oregon Department of Transportation (ODOT), 2021,
Standard Specifications for Construction.
American Society of Civil Engineers (ASCE), 2018, ASCE Standard 68-18: Permeable Interlocking Concrete
Pavement.
American Society for Testing and Materials (ASTM) International, 2018, D3385,Standard Test Method
for Infiltration Rate of Soils in Field using Double-ring Infiltrometer.
ASTM International, 2019, E1903,Standard Practice for Environmental Site Assessments:Phase II
Environmental Site Assessment Process.
ASTM International, 2022, C478/C478M,Standard Specification for Circular Precast Reinforced Concrete
Manhole Sections.
ASTM International, 2022, D8152-18,Standard Practice for Measuring Field Infiltration Rate and
Calculating Field Hydraulic Conductivity Using the Modified Philip Dunne Infiltrometer Test.
Bumbaco, K.A., C.L. Raymond, L.W. O'Neill, D.J. Hoekema, 2024, 2023 Pacific Northwest Water Year
Impacts Assessment.
Cahill,T.H., 2012, Low Impact Development and Sustainable Storm water Management, McGraw-Hill.
Dalton, M., Mote, P.W., Snover,A.K. 2013. Climate Change in the Northwest:Implications for our
Landscapes, Waters, and Communities.Washington, D.C.: Island Press.
Debo,Thomas N. and Andrew J. Reese. 2003.Municipal Storm water Management, 2nd ed. Lewis
Publishers, CRC Press LLC. Boca Raton, Florida.
Fleishman, E., editor, 2023,Sixth Oregon Climate Assessment. Oregon Climate Change Research
Institute, Oregon State University, Corvallis, OR DOI 10.5399/osu/1161.
Greger, M., and Landberg,T, 2023, Removal of PFAS from water by aquatic plants, Journal of
Environmental Management, Vol 351, 29 December 2023.
Gresham, City of, 2025, Stormwater Management Manual.
King County. 1998.King County, Washington Surface Water Design Manual. Department of Human
Resources.
Lane, E.W. 1955. Design of Stable Channels.Transactions of the American Society of Civil Engineers,
Volume 120, pages 1-34.
Leopold, L.B.,and T. Maddock. 1953. The Hydraulic Geometry of Stream Channels and Some
Physiographic Implications. US Geological Survey Professional Paper, 252.
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National Resource Conservation Service (NRCS), 2007, National Engineering Handbook, Part 630
Hydrology, Hydrologic Soil Groups.
NRCS,Soil Texture Calculator, Multi-Point Texture Triangle at
https://www.nres.usda.gov/resources/education-and-teaching-materials/soil-texture-calculator
Oregon Department of Agriculture, 2024, Noxious Weed Policy and Classification System
Oregon Department of Environmental Quality(DEQ), 2019, Final Revised Willamette Basin Mercury Total
Maximum Daily Load.
Oregon Department of Transportation, 2014, Hydraulics Manual.
Oregon Invasive Species Council, 2025, https://www.oregoninvasivespeciescouncil.org/
OTAK. 2009, City of Lake Oswego Clean Streams Plan.
OTAK, 2022,Technical Memorandum: Stormwater Plan Review Procedures.
Portland, City of, 2020,Storm water Management Manual.
Seattle, City of, 2017,Subsurface Investigation and Infiltration Testing for Infiltrating BMP's, Stormwater
Manual—Appendix D.
Syranidou, E., Christofilapoulos, S, and Kalogerakis, N., 2017,Juncus spp. —the helophyte for all(phyto)
remediation purposes?, New Biotechnology,Vol 38, Part B, September 2017, pp 43-55.
Washington Department of Ecology, 2024, Stormwater Management Manual for Western Washington.
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APPENDIX A STORMWATER REPORT TEMPLATE
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STORMWATER REPORT
Date:
Building Permit#or Land-Use Case: Company Name:
Tax Lot Number: Company Address:
Nearest Address:
Proposed Stormwater Facilities: Contact Phone Name and Number:
Stormwater Facility Drainage Type
Type Tier (roof,driveway,parking lot,etc.) Impervious Area Treated
Total Impervious Area
Describe development type and zoning of tax lot(or future zoning of completed
Project project). Discuss requirements of project including whether it is a Small or Large
Project.
Infiltration Rate: Discuss the infiltration test method, the test locations, and the depth
at which the tests were completed. State the median measured infiltration rate and the
calculated design infiltration rate.
Soil Description: Describe the predominant soil class on the property, whether
hydraulically-restrictive layers exist and at what elevation, and whether contaminated
soil or an onsite wastewater system is present on the property.
Geotechnical Hazards: Discuss slopes within 50 ft of the tax lot including any slopes
Existing that are 15%or greater. Discuss the presence or absence of weak soils and faults.
Conditions Discuss landslide risk including the presence of recent landslides(as defined by
DOGAMI)
Hydrological Constraints and Hazards: Discuss the groundwater elevation (or
estimated depth to groundwater), presence or absence of a wetland, stream, or
sensitive lands within 100 ft of the tax lot, and the elevation of neighboring properties
relative to the subject property.
Setbacks: Discuss setbacks applicable to the property.
" 114"'
Proposed Discuss the design infiltration rate,final contours of the property,final elevation at property
Conditions limits in relation to the neighboring properties. Using the existing conditions, discuss proposed
location(s)of stormwater facilities
Determine the type of stormwater facility that will be used to treat the impervious area created
Feasibility by the project. Using the existing conditions previously discussed and the design infiltration rate,
Analysis determine if a Tier 1 storm water facility is feasible or infeasible. If a Tier 1 infiltration facility is
infeasible, discuss whether a Tier 2 facility is feasible or infeasible. .
Flow Control Compare the pre-development flowrates with the post-development flowrates at the respective
Analysis(for Large 'sign storms. Discuss the number of orifices needed, if any, and their diameter, location, and
Projects only) elevation.
Using the results from the storm water model, discuss the pre-and post-development flowrates,
the existing capacity of the downstream public storm water system and whether storm water from
Downstream
Capacity and the project will cause the existing capacity to exceed 80%.
Backwater
Analysis Using the results from the storm water model, discuss whether backwater will occur at the design
storm, the area of flooding that is likely to occur, and whether neighboring properties and
buildings will be affected.
Summary Using the metrics discussed above, discuss how the proposed storm water management plan
complies with the requirements of the SWMM
1. Existing Conditions Map(including a storm water basin map)
2. Proposed Conditions Map
Appendices 3. Composite Utility Map
4.Storm water Model Calculations including time of concentration,pre-development flowrates,
post-development flowrates, and pipe capacity graphics(if applicable).
" 115"'
BASIC STORMWATER REPORT
Date:
Building Permit#: Company Name:
Tax Lot Number: Company Address:
Nearest Address:
Proposed Stormwater Facilities: Contact Phone Name and Number:
Stormwater Facility Drainage Type
Type Tier (roof,driveway,parking lot,etc.) Impervious Area Treated
Total Impervious Area
Project Describe the development type and zoning of tax lot(or future zoning of completed
project).
Infiltration Rate: Discuss the infiltration test method used, the location of the tests, and
the depth at which the tests were completed. State the measured infiltration rate and
the calculated design infiltration rate.
Soil Description: Describe the predominant soil class on the property, whether
hydraulically-restrictive layers exist and at what elevation, and whether contaminated
soil or an onsite wastewater system is present on the property.
Existing
Geotechnical Hazards: Discuss slopes within 50 ft of the tax lot including any slopes
Conditions that are 15%or greater. Discuss the presence or absence of weak soils and faults.
Discuss landslide risk including the presence of recent landslides(as defined by
DOGAMI)
Hydrological Constraints and Hazards: Discuss the groundwater elevation (or
estimated depth to groundwater), presence or absence of a wetland, stream, or
sensitive lands within 100 ft of the tax lot, and the elevation of neighboring properties
relative to the subject property.
Setbacks: Discuss setbacks applicable to the property.
Proposed Discuss the final contours of the property,final elevation at property limits in relation to the
Conditions neighboring properties. Discuss proposed location(s)of storm water facilities
"'116
Discuss requirements of the project. Determine the type of stormwater facility that will be
Feasibility used to treat the impervious area created by the project. Determine if a Tier 1 stormwater facility
Analysis is feasible or infeasible. If a Tier 1 infiltration facility is infeasible, discuss whether a Tier 2 facility
is feasible or infeasible.
Delineate the impervious areas being treated by each stormwater facility on a map and provide a
Prescriptive Sizing able showing the stormwater facility, impervious area treated,prescriptive sizing factor used,
and the surface area of the facility.
Summary Using the metrics discussed above, discuss how the proposed stormwater management plan
complies with the requirements of the SWMM
1. Existing Conditions Map(including a stormwater basin map)
Appendices 2. Proposed Conditions Map
3. Composite Utility Map
"'117
APPENDIX B INFILTRATION TEST LOG AND REPORT TEMPLATE
118
INFILTRATION TEST LOG
Date:
Tax Lot Number: Company Name:
Nearest Address: Company Address:
Tester Name/Email:
(Soil Classification
Depth(ft,bgs) Soil Type I
Infiltration Test
Test Method: Test Hole ID#:
Testing Depth,ft bgs: Test Hole Diameter or Length/Width,ft:
Presaturation Time: to
Time Measurement Water Level Drop Infiltration Rate
Time Interval (hr) (ft) (ft) (inches/hr) Notes
Test#1
NA NA NA I
I
I
Test#2
NA NA NA
I
Test#3 I
NA NA NA I
I
Infiltration Rate:
Measured: inches/hr Design: inches/hr
119
INFILTRATION REPORT
Date:
Tax Lot Number: Company Name:
Nearest Address: Company Address:
Contact Name
Project Include client name and address.
Description Describe project and existing conditions including slope and photos
Discuss the infiltration test methods, number and descriptive location of the tests,
Infiltration depth at which the tests were completed, the measured infiltration rates, and the
design infiltration rates.
Soil Describe the soil class at the depth of each test. Describe whether hydraulically-
Description restrictive layers exist, the elevation (ft, bgs), and the depth of the layer.
Geotechnical Discuss geology and geotechnical hazards.
Hazards
Hydrologic Discuss the groundwater elevation (or estimated depth to groundwater)and the
Hazards presence or absence of a wetland or sensitive lands within 100 ft of the tax lot.
Summary State the median infiltration rate and summarize whether an infiltration facility is
appropriate for the project using the above information as evidence.
1. Map showing the location of test holes.
Map
2. Map showing the location of geotechnical and hydrological hazards, if any
Appendices
3.Attached Boring Logs
-120"'
APPENDIX C PLANT SELECTION AND APPROVED PLANT LIST
Right Plant —Right Place Plants play an important role in the function of a stormwater
facilities and,with the right plant palette, can also contribute
For a vegetative stormwater aesthetically to the surrounding area. Landscape design must
facility to function long-term,the thrive under local conditions such as soil moisture, light
landscape professional must
consider plant placement and exposure, nearby infrastructure, setbacks, sight distance
optimum growing conditions. requirements, expected pedestrian traffic, and existing nearby
Vegetative facilities are required plant communities. Plants must adapt to local micro-climates at
to maintain a minimum plant private facility locations without permanent irrigation. In
coverage at plant maturity. The addition to the "right plant right place" concept, it is important
width and height of each plant to choose plants that do not require fertilizers or pesticides to
species must be considered,as thrive.
well as the number of plants in
the facility,to provide adequate C.1 Vegetative Diversity
coverage.
Healthy and densely planted vegetation in a stormwater facility
improves its performance. Each vegetated stormwater facility requires a minimum number of plant
families to avoid catastrophic die-off within the facility due to weather conditions or pest infestations.
Diverse vegetation in stormwater facilities significantly improves stormwater treatment and plant
survivability. Plant diversity helps to:
• Reduce sediment. Plants act as physical filters by capturing sediment and associated
hydrophobic pollutants. Facultative plant species are : •-_ =fi
fa^ r
particularly suited to reducing sediment load because A .g.'',,=-.sue '- +,� +'4
of their ability to thrive in saturated soils or "'j vf,� -
el
unsaturated soils. 1 3, 1,
• Reduce stormwater velocity.Vegetation reduces the . ,�� t) §� •�, f , R�
velocity through a stormwater facility and allows r�� 3','r ���i.� �fp-o- 1 �,i,'{�, ,t+y
additional settlingtime for pollutants in stormwater. 't, k , `i �. ,,0 , ;1' A
• Increase infiltration. Plant families have different ::�R`. '141., ly;`;li(i 1''�'� f$.�,id,.lifiF "'t
types of root systems (fibrous vs tap) and depth. Root Plants play an important role in filtering
diversity protects a soil's infiltration capacity. sediment and pollutants from stormwater
• Reduce erosion. Fibrous root systems are more effective in preventing erosion in a stormwater
facility especially near inlets and other areas of high velocity or elevation drop.
• Reduce pollutant concentrations. Plants absorb pollutants
through their roots and store them to varying degrees. For stormwater filtration
example, carex rostrata (beaked sedge) is excellent for results in sediment removal
absorbing PFAS (Greger and Landberg, 2023). Plants in the as well as the reduction of
Juncus family are suitable for the removal of many heavy metals,phosphorus, and
metals (Syranidou, E., et al., 2017). other pollutants.
-121"'
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it`�4. _ R« -� jt: A,.
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fi
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iiiit
- Clean Water Services
Constructed wetlands have a variety of trees,shrubs,grasses,and
groundcovers. They benefit wildlife and reduce pollutants.
C.2 Invasive Species, Native Species, and Naturalized Species
Native species are plants that have adapted to our climate and
are a normal component of our ecosystem.They provide
.i, . {. benefits to our waterways and to our wildlife. Native species are
r -� � "' approved for all stormwater facilities and their use is strongly
':' , _ -4,: encouraged for landscaping throughout the city.
",
` "" 41101.1s s ti1 Plants are defined as naturalized, invasive, or noxious by the
* + , A � ,..•�i Oregon Department of Agriculture (ODA) based on tendencies to
become the dominant plant in a vegetative community, their
ability to spread quickly, and the difficulty involved to eradicate
Himalayan blackberries are a common them from an area. Invasive and noxious plants are prohibited
invasive plant in Oregon.
from use in a stormwater facility(see Table C-1).
Naturalized species are plants that are introduced from other areas of the world but co-exist with our
native species without dominating the ecosystem.They provide some benefit to wildlife but, in general,
do not provide a main food source or habitat for native wildlife.
Invasive species do not provide wildlife habitat nor are a main food source for native wildlife. Noxious
species are a subset of invasive species that are extremely hard to eradicate once they have colonized
an area. Invasive and noxious species are prohibited from use in stormwater facilities.
While Table C-1 provides a wide list of plants that are known to be noxious or invasive in Oregon,
the landscape professional must consult the current invasive lists available from ODA and the
Oregon Invasive Species Council to determine whether a plant is prohibited in a stormwater facility.
-122"'
Table C-1. Invasive and Noxious Weeds in Oregon
Plant Latin Name Plant Common Name Plant Latin Name Plant Common Name
Acaena novae-zelandiae Biddy-biddy Hypericum perforatum St.John's Wort
Aegilops,spp Goatgrass Impatiens glandulifera Policeman's helmet
Adonis aestivalis Pheasant's Eye Iris psuedocorus Yellow Flag Iris
Ailanthus altissima Tree of Heaven Isatis tinctoria1 Dyer's Woad
Alhagi pseudalhagi Camel Thorn Linaria,spp Toadflax
Alliaria petiolate) Garlic Mustard Lagarosiphon major Curly waterweed
Amorpha fruticose Indigo Bush Lamiastrum galeobdolun Yellow Archarngel
Anchusa officinalisl Common Bugloss Lathyrus latifolius Perennial Peavine
Arundo donaxe Giant Reed Lepidium,spp2 Whitetop, Pepperweed
Brachypodium sylvaticum False Brome Limnobium laevigatum South American spongeplant
Bryonia alba White Bryonia Ludwigia,spp2 Water primrose
Buddleja davidii Butterfly Bush Lysimachia vulgaris Garden Yellow Loosestrife
Butomus umbellatus Flowering Rush Lythrum salicaria Purple Loosestrife
Carduus,spp Thistle Myriophyllum,spp Watermilfoil, Parrotfeather
Chondrilla junceal Rush Skeletonweed Nymphoides peltate Yellow Floatingheart
Centaurea spp. Knapweed,Star Thistle Odontarrhena spp Yellow tuft
Cirsium,spp Thistle Onopordum acanthium Scotch Thistle
Clematis vitalba Old Man's Beard Orabanche minor Small broomrape
Conium maculatum Poison Hemlock Peganum harmala Wild Rue
Convolvulus arvensis Field Bindweed Phragmities australis Common Reed
Cortaderia jubata Jubata Grass Pilosella,spp2 Hawkweed
Crataegus monogyna English Hawthorn Phalaris arundinaceal Reed Canary Grass
Crupina vulgarise Common crupina Potentilla recta Sulfur Cinquefoil
Cuscuta japonica Japanese Dodder Pueraria lobata Kudzu
Cynoglossum officinale Houndstongue Ranunculus ficaria Lesser Celadine
Cyperus esculentus Yellow Nutsedge Rosa canina Dog Rose
Cytisus,spp2 Broom Rosa rubiginosa Sweet Briar
Daphne laureola Spurge Laurel Rubus ameniacus Himalyan Blackberry
Delairea odorata German Ivy Salvia aethiopis Mediterranean Sage
Dipsacus laciniatus Cutleaf teasel Salvinia molesta Giant Salvinia
Echium spp2 Buglass 5enecio jacobaeal Tansy Ragwort
Egeria densa S American Waterweed Silybum marianum Milk Thistle
Erica lusitanica Spanish Heath Spartina,spp Cordgrass
Euphorbia,spp2 Spurge Sphacrophysa salsula Swainson Pea
Fallopia,spp Knotweed Tamarix ramosissimal Saltcedar
Galega officinalis Goatsrue Taeniatherum caput Medusa head Rye
Geranium,spp Geraniums Tribulus terrestris Puncture Vine
Hedera,spp Ivy Tussilago farfara Coltsfoot
Heracleum mantegazzianum Giant Hogweed Ulex europaeusl Gorse
Hydrilla verticillate Waterthyme Ventenata dubia Ventenata Grass
1—Noxious;2—Some species are noxious;Source:ODA,2024 and Oregon Invasive Species Council,2025
—123—
C.3 Plant Selection
Choosing the plant palette for a stormwater facility should take into account the micro-climate at the
facility, plant availability, and maintenance of the facility(see Figure C-1). Information such as the post-
construction landscape and desired aesthetics will also affect the final landscape design.
C.3.1. Post-Construction Landscape and Microclimate
The design professional should become familiar with the post-construction conditions and microclimate.
Some questions to consider include:
• Is the adjacent area to be used for parking or bike lanes (plant overhang)?
• Is the adjacent landscape a street or a backyard?
• What will be the post-construction light conditions (morning sun, afternoon shade, sun all day)?
• Is the facility located near a tall building or high traffic street where plants will be buffeted by
wind?
• Is the entity responsible for maintenance of the facility a homeowner, business, or the City?
C.3.2 Plant Palette
Select plants that will provide for year-round water quality and aesthetic functions.A stormwater facility
can contain up to 10%forbs to improve aesthetics.
Vegetation coverage within the planted facilities must be shown on the site plan, with a diagram and
calculation for a minimum of 100%coverage at maturity. 100% mature coverage must be achieved
within one year following construction and shall never drop below 90%coverage.
C.3.3 Mature Plant Considerations
Consideration should be given to the mature height, as well as width, of the plants installed in a
stormwater facility. Sightlines need to be preserved at intersections for vehicular and pedestrian safety
when the plant is at maturity. If trees or large shrubs are being installed,the stormwater facility is
required to have 2 feet of topsoil to provide adequate room for the tree to mature.This is especially
important for public facilities.
C.4 Plant Availability
The landscape professional must ensure that plants are available for the
Permanent irrigation expected planting timeframe. Fall and early spring are the most common
is required in public times for planting because they allow some root growth prior to the plant
stormwater facilities. stress that occurs during the dry summers in the City.A temporary irrigation
system must be installed if the project schedule assumes that plants will be
installed from early summer to early fall.
-124"'
Collect Project
Information Permanent
(sun/shade, irrigation Public Facility? _Yes Irrigation
needs,maintenance Required
access)
No
elect plants from
Design Irrigation
City-approved
System
plant list
0
i=
u
w Create Planting
Check Plant Plan and
z Not Availability with
Q —Available Landscape Sheet
a Nurseries for Construction
N Plan Set
w
Available
Review Plant
Requirements
No Will plants survive at Yes
location with minimal
maintenance?
Figure C-1. Considerations for Plant Selection in a Stormwater Facility
C.5 Plant Maintenance
The landscape professional must choose plants that have maintenance requirements commensurate
with the experience normally associated with the type of responsible party.A stormwater facility for a
SFR project must contain plants that are easy to care for whereas a business that is likely to have a
landscape professional on staff could have a stormwater facility with plants that require more attention.
The following questions should be considered:
• Does the planting design provide easy access for maintenance?
• Will plant roots or overhang negatively affect inlets, outlets, or pedestrian traffic?
• Are the plants prone to diseases that require pesticides, herbicides, or fungicides? Maintenance
" 125"'
of plants in stormwater facilities cannot include the use of pesticides, herbicides, or fungicides.
• Do the plants require regular pruning? Plants where pruning will adversely affect the mature
shape of the plant due to sightlines, overhead power, or other utility conflicts must not be
installed in the stormwater facility.
Native Plants
Native species are a priority for storm water facilities. They:
• Are adapted to local soil,hydrology, and climate conditions.
• Protect the infiltration capacity of soil in the storm water facility.
• Compete with invasive species to prevent monocultures.
• Are more resilient to pests and diseases.
Native vegetation provides the following benefits for storm water facilities. They:
• Blend into adjacent natural areas, open spaces, and
neighborhoods.
• Create a park-like visual experience for the community.
• Provides wildlife habitat(food and shelter).
• Encourage the presence of pollinators.
-126-
C.6 Plant List
-127"'
Lake Oswego Plant List: Rushes � � ,.. rt
(V ' r O
GREGo�
N4. ate'+
N
CO Z d _
cc) 2 E ad+
C = y
Ua 7"O Cof tote s 3 a0
L ;
�t m �+'~ Purple flowers in spring.
r Juncus acuminatus
s f' v ,, j,- Wet Sun to Part Sun 3 ft 3 ft Drought tolerant.Attracts
' `1 Ta Taper-Ti Rush
:s, +r•!}• .[� + .' e‹, p p birds and pollinators.
irr .
Evergreen.
I
�t+�<�r' S F � Brown flowers in summer.
�`\ , -. Juncus effusus var
+''',. pacificus Moist to Wet Sun 2 ft 3 ft Grass-like.
- Pacific Rush Attracts birds.
'-ei -,. .'he
‘..al
___ __ _
-+. r
..... Th
L! R 1
r i " a' Iris-like leaves.
t a Juncus ensifolius Moist to Wet Sun 2 ft 2 ft
; -* Dagger-Leaf Rush Attracts birds.
y r._:^ '•
,.. t. „:, , ,..,,,,„
Nit \ti',\� `C,-, , a
iM y 3 4 •
-3-..,..',1„:„..,,..Y,; ,II„ 'AI C, Juncus occidentalis
—? py yL 4 , Moist to Wet Sun 1 to 2 ft 2 ft Evergreen
r"� Western Rush
r r f
�r4 1 i2 A''' � "-..< Juncus patens Blue-green foliage with clustered
Vtrifi y, Moist to Wet Sun 2 ft 2 ft brown seedheads in summer.
,: 3 ,,.r� Spreading Rush Attracts birds.
. °• t Evergreen.
r/-
' / ' . a,t
)Tiz :
t.
t
, /'? ri . ,�
i soft Rush Juncus effusus Moist to Wet Sun 1 to 2.5 ft 1 ft Semi-evergreen.
f
—,
"> %' Scirpus microcarpus
s
\' Small-fruited Bulrush Moist to Wet Sun to Part Sun 2 ft 2 ft Semi-evergreen.
Lake Oswego Plant List: Sedges °,. ��}V �- O
GREGD/
C .. CN
E E 1
R p I
N w7 v iV
E n 3 *' c
i n aai •d v 0L
v
vsct x 3 a0
• otis r...
41
F, t�'�` r X �;'" Dense spreading sedge with
li' i y``., _ Carex morrowii foliage effect of dark green
i s Moderate to Wet Part Shade 1 ft 2 ft
t" .--�' '., r, Ice Dance Sedge with white borders.
,ilk -• 3 ��.. - to Shade
• ip 1.1
, Evergreen sedge that typically
T4?# °1- grows in dense weeping clumps
Carex comans
w d y: Moist to Wet Sun 1 to 2 ft 1 to 2 ft of thin hair-like leaves.
New Zealand Sedge
�� W .
1:;.:1. C& v7 is
4' r ) Good for slowing
1 '� flow and trapping
' Z f., Carex densa pP g
�s Moist to Wet Sun to Part Sun 2 ft 2 ft
sediment.
�� �, � �, . �- Dense Sedge
' iS ' \
r \ Evergreen.
k'cit����FiJ LOl}/ f,. 1
��� i�,YSif ' f r4 f;r� Pleasant colour that
m¢°''JkkK Grp f �4'f'' changes throughout the
y ! • �1 Carex dipsacea
7-7
t Moist to Wet Sun to Shade 3 ft 1 to 1.5 ft ::::vergreen
.
:-` ti 1 r
► ' +t i V I'
f'�; ,,' , Carex obnupta 2 ft Upright seed heads.
i.,, ` �� 1 k, Moist to Wet Sun to Part Sun 3 ft
,� r ` Slough Sedge
er
+y n� 1 • . " This chocolate colored sedge is
'at '"•. Carex tenuiculmis an extrraordinary complement
.f ? Moderate to Moist Sun to Shade 1 ft
,.r New Zealand Hair Sedge 2 ft to any garden.
,A,,. r1 -
_v t �( " Evergreen.
Yl3y
t.
ti�',.A`` V , ` " . Carex testacea
} L Moderate to Wet Sun to Part Sun 2.5 ft 2 ft Lightgreen leaves that developred
; : "e Orange Sedge g
L ri !� or orange highlights.
4� E�
Lake Oswego Plant List: Ferns °x. , �
GREG07...."\..>"
CD N d N
C N CI
0 c.
z2 Niy
aC i v>O 0
_G N dj t M 4-, R bl)O C a O
2 r CR
Gv) ore 2
3 aU
Delicate fronds with black
1 i- rr Adiantum pedotum Moist to Wet Part Sun to Shade 2 ft 1 to 2 ft stems. Prefers shade.
-«+• • Maidenhair Fern Will go dormant in hot
temperatures.
.41-; q\ f _
tt
i ., +r•e Athyrium filix femina Large delicate leaves.
k,.^* 1 .t, ;" ..• Moist to Wet Part Sun to Shade 3 ft 1.5 ft
• ' , t•, w Lady Fern Attracts birds.
tt,,
• ' :,,
Blechnum spicant Attracts birds.
Moist to Wet Part Sun to Shade 2 ft 1.5 ft
� -� Deer Fern Evergreen.
ii
{ '''~' Attracts wildlife.
<'`,�; Dryopteris arguta Moist Part Sun to Shade 3 ft 3 ft
Wood Fern Evergreen.
/, .—
y
' r Gymnocarpium Bright green triangular fronds.
r'• • disjunctum Moist Part Sun to Shade 2 ft 4 ft
Attracts wildlife.
�,,, Western Oak Fern
Polystichum munitum Attracts wildlife and birds.
t 's" "� it,;lea; Sword Fern Dry to Moist Part Sun to Shade 3 ft 3 ft
Evergreen.
'<: ,' ; - , Woodwardia fimbriata
i :L Moist to Wet Part Sun to Shade 6 ft 3 ft Evergreen.
•tv4-. .. "i' + Giant Chain Fern
Lake Oswego Plant List: Grasses and Sed u ms
V(jC. � O
OREGO�
N
. .
C N 0
o
�z N H
c d E «
o 3 ;u
C)co 2 to rY 2 a C)
t .
Reddish brown narrow and
erect(spike-like)seedheads.
,i fj 1 ,- Agrostis exarata
Moist to Wet Sun to Part Sun 1 to 3 ft 1 ft Cool season bunchgrass.
'p Ii� yet •. +,� Spike Bentgrass
., Attracts wildlife,birds,and
pollinators.
�� Drooping seedheads.
�' ` Si ` Cool season bunchgrass. Prefers
Bromus vulgaris�"'�' g Dry to Moist Sun to Shade 2 to 3 ft 2 ft shade.
1 I,( w. Columbia Brome
j'` N" f� f „ Attracts wildlife,birds,and
pollinators.
i//I . /�
t� y ` r Deschampsia Nodding seedheads.
caespitosa
Moist to Wet Sun to Part Sun 1 to 3 ft 2 ft Cool season grass.
= � Tufted Hairgrass
Attracts wildlife,birds,and
"`';' ,. � ". — pollinators.
I
. i,' '` Succulent groundcover with yellow
w Sedum oreganum
r " 4 r ' a flowers from spring to summer.
`1. ti s sr Dry to Moist Sun to Part Sun 0.3 ft 1 ft
Oregon stonecrop Attracts pollinators.
* -rc+a Evergreen.
°"(
5
a °- Succulent groundcover with
r Sedum spathulifolium yellow flowers in spring.
�'�� Dry to Moist Sun to Part Sun 0.5 ft 1 ft Attracts birds and pollinators.
": . '_ Broadleaf Stonecrop
� i - Evergreen.
4:‘A E
Lake Oswego Plant List: Perennials _F r`,
`V On
OREGOC-'
Deciduous varieties must not exceed 10%of planting area
E E c 0 c0i
co ca 0 = +•
ZZ N y 0cc., 2 E
Qt= o iu 1�
Ec u g t ,. m
Ear o cor a cc'a
0co rncr i 3 dU
i'(
Blue,purple,or white flowers in
Anemone oregano 0.25 ft late spring and early summer.
• Moist Part Sun to Shade 0.5 to 1 ft
Oregon Anemone Attracts birds and pollinators.
i
Blue and white flowers in late
v, Aquilegia coerulea spring to early summer.
' '.. ;4 Colorado Blue Moist Shade 1 to 2 ft 1 ft Attracts pollinators.
*. + Columbine
Plant in the fall(needs cold to
:f k! germinate).
:x;t
Red to orange flowers in spring.
4-
Aquilegia formoso Moist Sun to Part Sun 3 ft 1 to 2 ft Attracts pollinators.
Red Columbine Prefers well-drained soil.
1 4' 'Y,
t_k ?� ,:, 1,0k04.4., - ,rr: - ,...
4lit
, Purple flowers from
" z+ Astersus icatusi .� ?�:y» p Dry to Moist Sun to Part Sun 1 to 1.5 ft 1 ft summer to fall. Attracts
{".- .A Douglas Aster
birds and pollinators.
f
•11 .•.a y r— I` -0,
•
` yey Magenta to rose-colored
1,_ �,"� } Chamerion ougustifolium
4. •'•" 37 ?'� Fireweed Dry to Moist Sun to Part Sun 1 to 6 ft 1 ft flowers from summer to fall.
-' 'VI
t
irk y
.sPurple tubular flowers insrin
h -r ":'« Delphinium menziesii P g
0114 "t' , '"dit Dry to Wet Sun to Part Sun 1 to 2 ft 1 ft to early summer.
.,:i . Menzies'Larkspur
il 4roj't • ''.'!-.
tic Attracts birds and pollinators.
r.
- Pink flowers spring to
c.- Dicentra formoso summer.Attracts birds and
Pacific Bleeding Heart Moist Part Sun to Shade 1.5 ft 1.5 ft pollinators.
:M ..;r'' Will go dormant during hot
temperatures.
litIPT%\
A ELake Oswego Plant List: Perennials
\L) visolollr.,,,,, C:2)
GREGOCS
Deciduous varieties must not exceed 10%of planting area
H
d N I
y
H
t r
R
N C 2 3 d U
\ -t', Pink flowers in summer
'
followed by edible berries. Also
ip ''. Gaultheria ovatifolia Part Sun known as Oregon Teaberry.
Wintergreen Moist to Wet 0.25 ft 1 to 3 ft g
! Attracts birds and pollinators.
Evergreen.
•
i; -' Gentiona porryii
, x•' v • ,�.s Mountain Gentian Moist to wet Sun 1 to 2 ft 1 ft Blue flowers in summer.
s k
,--� tr.__ - _` Hydrophyllum teniupes White to lavender bell-shaped
;c Moist Sun to Shade 1 to 3 ft 1 ft flowers in early summer.
4 ,�y,,� ms -;�e'j.",' Pacific Waterleaf
,�
4�� . r '`ii i Iris tenax Purple flowers in spring.
'^"' r Dryto Moist Sun to Part Sun 1 ft 1.5 ft
-•/''� /" ,•� Oregon Iris Attracts birds.
hid: M' tie
Purplish blue flowers in summer.
':,-A- r:`-' ,p7 X1 Lupinus polyphyllus Moist to Wet Sun to Part Sun 3 ft 2 ft p
+_; Large-Leaved Lupine Attracts birds and pollinators.
0--
--y
NtN+'F :,..is.-as! Liriope spicata Lavender flowers late
Moderate to DrySun to Part Shade 1 to 2 ft 1 to 2 ft
iiiek
iS�j r Creeping Lilyturf summer.Goundcover,
;"` I.`r �• speeding.
Fragrant creamy white panicle
Matonthemum of flowers in early summer
racemosa followed by red berries.
4r.. r Moist Part Sun to Shade 1 to 3 ft 1.5 ft
^t. Astscii- -4 ` Western False Attracts wildlife and birds.
: 4ik Solomon's Seal
Slow growth.
O-t vA Eciii
Lake Oswego Plant List. Perennials ri �\
ot V" • ) o
OREGOC‘
Deciduous varieties must not exceed 10%of planting area
a) to o
EE
tom c c
zz N „ N
c o to E 8
♦7 t= Y - FY U
E ar o CIS — 'a = to
R
cite m'� s 3 av
ft -`'g' ' , • •atc`Mimulus guttotus Yellow tubular flowers in
• '` r,, Moist to Wet Sun to Part Sun 0.5 to 2.5 ft 0.5 ft summer.
*.tom _v Common Monkeyflower
a ,z�f a, ,1^;' ,. Attracts birds and pollinators.
hT
Blue flower with white center in
4 N moph la menziesii spring and early summer.
Moist Sun to Part Sun 0.5 to 1 ft 0.25 ft
Baby Blue EyesAttracts pollinators.r7C-4. 7/1,. .s,•II- .1
i o i
Yellow flowers in summer.
, . _fros_
`'••-•& f Hypoxis hirsuto Attracts birds and
Yellow Star Grass Dry to Moist Sun to Part Sun 1 ft 1.5 ft
' pollinators.Needs well-
drained soil.
"` Purple flowers in summer.
"• f �" Penstemon serrulatus
e4o Moist to Wet Sun to Part Sun 1 to 2 ft 1 ft Attracts birds and pollinators.
". 'r Cascade Penstemon
r5, is 0i fi
Semi-evergreen. •
ti
k' J ) � I
.�' +` ! Sagittaria latifolia White flowers in summer to
t i Wet Sun to Part Sun I.to 3 ft 1 ft earl fall.
,i,v_,, Wapato Y
IOW AP
Rosy pink flowers in summer
Sidalcea cusickii Moist to Wet Sun to Part Sun 2 to 5 ft 1 ft that deepen in color as they age.
l __'.2, 4 Cusick's Checkermallow
Attracts pollinators.
X
Viola semperyirens
� Yellow flowers in spring.
"" Evergreen Violet Moist to Wet Part Sun to Shade 0.35 ft 0.25 ft
Agrel
Evergreen.
A"._Y. 7
r.' — -
/O�t,AE��
Lake Oswego Plant List: Medium to Small Shrubs - �!''N�,
n
v � . O/
°REG0-/
C
No
tQ N N *a. N
Z>_
C U a E y
o
"O d
y C �p
U
d r 2 3 dU
_
P - - ----fit--
4 rr r ,� ^r"r1^ Small pink-white flowers
,, 'yt Ceanothus velutinus
�'� l a 1. Y�ti Snow Brush Dry to Moist Sun 2 to 6 ft 3 ft and white berries.
lb gi_ Attracts birds.
Yor
Evergreen.
Pink flowers in spring followed by
'' blue-black berries in the fall.
Salal Gauitheria shallon
. .7mGrows taller in shade.
111111
�+► ' -", Dry to Moist Part Sun to,Shade 1 to 3 ft 3 to 4 ft
'3�"'t 1.t.-
Sala! Attracts birds and pollinators.
Evergreen.
Yellow flowers in spring followed
t. 'i =I Mahonia aquifohum by edible fruit. Bronze fall color
,;ir rsue Tall Oregon Grape Dry to Moist Sun to Part Sun 4 to 6 ft 4 ft4grlf Attracts birds and pollinators.
Evergreen.rid'
--`ri ' ' 7—iv.-
� Yellow flowers in spring followed
"' , (' + by blue fruit.
r< > , .. Mahonio nervosa
...r� Dry to Moist Sun to Part Sun 2 ft 2 ft
3l✓ r• Dull Oregon Grape Attracts wildlife and birds.
1 rf . Evergreen
Sa >' r-_ i . a
mat'„ ,w, `'
.x Fragrant white flowers in late
r "4' ''. spring to midsummer.
MoPhck Orangeelphus lewisii Dry to Moist Sun to Part Sun 5 to 7 ft 3 to 5 ft
;,,' Mock Attracts birds and pollinators.
•
Prefers well-drained soil.
j , ;r "' `, Reddish pink flowers in early spring
ram ` » Ribessanguineum followed by edible bluish black
" " Dry to Moist Sun to Part Sun 4 to 8 ft 7 ft berries in fall.
z Red Flowering Current
:''�.'-., ' ' Attracts birds and pollinators.
�P Prefers well-drained soil.
r .,� , ' 1
a j' --`'T-7 Pale pink fragrant flowers in
" #' Fir Fr Rosa Gymnocarpa 3 ft summer with orange-red rose hips
t'rF fr Moist to Wet Sun to Shade 3 to 5 ft
r Baldhip Rose in the fall.
4110
cit r ° Soft spines(no thorns).
i
l
O�� E �srz-.
Lake Oswego Plant List: Medium to Small Shrubs (� n\
1� o)
\\REGOa /
y y
110
m w c=_t:
R m = w,
zZ dC
C U C
O E y V -
OU 7 N 9 AL —�
�� w� aC)
. i �,- . '.4a - It Fragrant flowers in late spring to
�'a-+ ''4.J ; midsummer with large scarlet rose
R: Rosa nutkana
. me.. ''e x 'N,. .�' Moist to Wet Sun to Part Sun 5 to 7 ft 4 to 5 ft hips in the fall.
_ .,.t,�. Nootka Rose Attracts birds and pollinators.
�A J
,,� Curved thorns.
^ "' "` White flowers in spring followed by
F •�i ?' pinkish red fruit in the summer.
Rubus parviflorus
Thimbleber Moist to Wet Part Sun to Shade 5 ft 5 ft large soft leaves.
r . ry Attracts wildlife,birds,and
' pollinators.
` Magenta flowers in the spring
Rubus spectabilis followed by an orange-red fruit in
�G IIllir7r Salmonberry Moist to Wet Sun to Part Sun 6 to 8 ft 8 ft the summer.
° '+ Attracts wildlife,birds,and
`+ pollinators.
,i a g. r_. Upright pyramidal dark pink
- a•. Spiraea douglasii flower in summer. Shrub shape is
Moist to Wet Sun to Part Sun 4 to 5 ft 4 to 6 ft more compact in the sun.
=^ '4 .,i ;" Douglas Spires
-`';j -.`1 4•- 4*. Attracts birds and pollinators.
• 1µ� Pink bell-shaped flowers in late
' - —a,4'7 .„„,„La, spring to summer followed by
^ ' edible dark blue berries in the fall.
f s-;y- ' * Vaccinum ovatum Dry to Moist Sun to Shade 3 to 6 ft 3 ft Slow growth.
n 1'. 4r Evergreen Huckleberry
` '. .Y Attracts wildlife,birds,and
1,gab ,z.• pollinators.
t +�1 .J• '
. ."i.. °.:•. :' ' Evergreen.
I.
' Yellow or pink flowers in spring
%. : Vaccinum parvifolium followed by red tart berries in the
}� Dry to Moist Part Sun to Shade 3 to 6 ft 4 ft fall.
4< Red Huckleberry
• "' Attracts wildlife,birds,and
y"' > ; pollinators.
White flowers in late spring or
1 early summer followed by red
Viburnum edule 4 ft edible berries. Red fall color.
Highbush Cranberry Moist to Wet Sun to Part Sun 6 ft
Attracts wildlife,birds,and
pollinators.
111.11111 i
AlKf,,.;_,...:—.
ke Osw La ego Plant List Small Trees or Large Shrubs
\,zt,E. 00-\
mcp J
i
mE;= tA t
E0 3d a
G . 5.cin
hx x 3 a.0
-4sr2 J
",;. ^�`• Multiple stemmed tree in sunny
areas. Grows as a vining shrub in
1E --�. Acer circinatum Moist to Wet Part Sun to Shade 15 ft 10 ft shady areas.
• tif, Vine Maple Red-orange Fall color.
Attracts wildlife and birds.
ii .t . rill White flowers in earl y spring
V P g
�' Amelanchier olnifolio followed by edible black fruit.
i' .. Dry to Wet Sun to Part Sun 10 to 18 ft 10 ft
Serviceberry
M Attracts birds and pollinators.
l'A. / •.. .
>a.
T--"-----
Pink flowers in early summer.
r+ ; ,; Reddish flaky bark for winter
.4,- „ , Arctostaphylos interest.
. . :i•: . • ...:. columbiana Dry to Moist Sun 10 ft 10 ft
Hairy Manzanita Attracts birds and pollinators.
~ q Evergreen.
'.,.k+, k� �, f y°. Fragrant blue flowers in spring and
fall.
• ._'• `,• •` Ceanothus thyrsiflorus
.14-e• Dry Sun 15 ft 6 to 8 ft Attracts birds and pollinators.
,, -1' Blue Blossum
f •. . Evergreen.
•
fllJ1 �t�
J'� f Large white to pink blooms in
4 .� `M'fii. Cornus nuttollii Moist to Wet Part Sun to Shade 20 ft 10 ft spring. Orange o purple fall color.
34`.. r.,.,-,am. ,) Pacific Dogwood
• 'g' � White flowers in late spring. Blue
c
N. -c
�► sw. inedible fruit in summer.
,,,i..� Cornus sericea
ti,• r*`, Moist to Wet Sun to Part Sun 8 to 10 ft 6 to 8 ft Red bark in sunny areas.
%` a- .,It • , lit Red-Osier Dogwood
`7 - 0
+ ; Attracts birds and pollinators.
�• • Edible nuts. Yellow leaves in fall.
- Carylus cornuta
' Dry to Moist Part Sun 12 ft 12 ft Attracts wildlife.
,. is ", Beaked Hazelnut
�.
r Prefers well-drained soil.
fi:' A G , li . .
.c, , a t,
Lake Plant t L List: Small Trees or Large Shrubs �„'
..l n)
c;)
0 co 5,
E E c m
iv
N y c
c(..) 22 E
4.
f+ �' G1
Ec ti •_ t ,�
E .o c a 1 -0 c R
"H "�..,.f-...,... .:,..'„,:c' Euonymus occidentalis
Moist Red and
x:<J. 44f.4.,-'':=•n7'', Western Wahoo Part Sun to Shade 10 to 15 ft 10 ft yellow fall color.
White to cream flowers in late
-� - F spring to late Sumer.Flowers
v Holodiscus discolor turn light brown and stay ony, ;a+�° Dry to Moist Sun to Part Sun 10 ft 6 ft plant through winter.
Oceanspray
Vase-shaped.
- — • Attracts birds and pollinators.
it
Yellow flowers in spring and
Lonicera involucrata summer.Paired inedible black
Black Twinberry Moist to Wet Sun to Part Sun 10 to 12 ft 7 ft berries.
0';' =a' 1 Attracts birds and pollinators.
Fragrant pinkish white flowers in
F
spring.Edible tart apples and
Malus Fusco orange-red color in fall.
Moist to Wet Sun to Part Sun 10 to 30 ft 15 ft
r� r + Pacific crabapple Attracts wildlife,birds,and
far
.....:
'.r _' '= pollinators.
l \y,�.‹.
• f < , , ""
"'- ' ip .�. .V'�►.. White flowers in early spring.
4r .c' ''(.i Oemleria cerasiformis
Bluish-black plum-shaped fruit in
••• '�dfT, +�,ar, f Dry to Moist Part Sun to Shade lO ft 5 ft fall.
• Indian Plum
.A` •', -`\; Attracts wildlife and birds
r` a.
n ' - White flowers in late spring. Red
Physocarpus capitatus seed clusters in summer and fall.
.
g."• < .i"e `rVt. Pacific Ninebark Moist to Wet Sun to Part Sun 10 to 12 ft 5 to 8 ft Shredded bark for winter interest.
�, n-
r (k4-' .'t, ,�PIvtf ` Attracts birds and pollinators.
*>. Fragrant white flowers in spring
- followed by inedible red cherries
Prunus emarginata which are favored by cedar
Bitter CherryMoist to Wet Sun to Part Sun 20 ft 15 ft waxwings.
I Attracts wildlife,birds,and
pollinators.
O*€;:-
Lake Oswego Plant List: Small Trees or Large Shrubs (�IV0)
\REGG/
C1
Z Z N d -
U v 5
0 p `io
p CC' DA P � l0
c.n 2 ins s 3 av
White flowers in spring followed
_ prunus vir by edible tart cherries in
o Moist to Wet Sun to Part Sun 15 ft 12 ft mmb
Common Chokecherry
r Attracts wildlife,birds,and
pollinators.
s�. Q •
K Rhamnus purshiana Shrub or small tree depending on
ies;?,,,_ ;""-`mil
Moist Sun to Part Sun 20 ft 15 ft
.4 • Cascara the conditions. Yellow fall color.
4- ¢ Tom " Dome-shaped white flowers
'4, •, 'i� ' Sambucus caerulea
r ., ' _\ �, ' Dryto Moist Sun to Part Sun 15 ft 15 ft followed by edible blue berries.
' Blue Elderberry
G.. .rli,-:',' 'p Attracts wildlife,birds,and
I+ ;/ •ti.-< + pollinators.
la .
',y �, J• Fragrant white flowers and red
/f* tom`
I.;° Sambucus racemosa berries.
/ I'r� ,'I, Dry to Wet Sun to Shade 15 ft 15 ft
.., ! ,1. y � , Red Elderberry
• 11 Attracts wildlife,birds,and
^ r ' a pollinators.
vii.....,
'3, Ak,, White flowers in early summer.
A, .ar m;;,t. i ,I,w: Sorbus s untai sis Tart red fruit in fall.
•.wti�y 's 4' +f, tr'S-c a • Dry to Moist Sun to Part Sun 10 to 12 ft 5 ft
t -4 '., Sitka Mountain Ash
y,. .i', i Attracts wildlife and birds.
Slow rowth. Cited height is at 10
5 :: 5:::::: ch40
Moist to Wet Sun to Shade 10 ft 10 ft
"'a. ►>ik' ', Evergreen.
�' . Small white flowers in spring
with black plum fruit in fall. Red
Viburnam dovidii 10 ft 8 ft fall foliage.
t '••S� • David Viburnam Dry to Moist Sun to Shade
il _
t:$0`.
w Attracts wildlife,birds,and
al" pollinators.
o�� Eos
Lake Oswego Plant List: Large Trees � �,
V _/ 0
OREGO"
N
E a, C0
an0�z N H
c c e E �:
° � 3 e
E 0 s s a, R
$ cCr to •"o cR
c�cn v')ix s 3 CO av
- *. Fragrant white flowers in spring
followed by red fruit in the fall.
l4 y�
Arbutus menziesii Attracts wildlife and birds.Peeling
Dry to Moist Sun to Part Sun 30 to 70 ft 20 to 30 ft bark.
i ` r Pacific Madrone
'. n r .� ,i14-. Needs good drainage. Slow growth.
,�.,�'4 Ever reen.
'' 11N, A It k
Not recommended for areas near
�s' •�• Betula papyrifera patios or parking areas.
-' "; Moist Sun to Part Sun 60 ft 20 ft
Paper Birch Peeling bark.
Attracts wildlife and pollinators.
r.
*,.�"'
r; ^xl1' `�' Fraxinus latifolia
.k Moist to Wet Sun to Part Sun 70 ft Attracts wildlife,birds,and
,�.� `' 25 ft pollinators.
^1�"\�. N ;� Oregon Ash
''•aa•te�' I ( IFP,/
/ Fragrant textured bark.
p `w.; , ,v _ Pin us Ponderosa Dry to Moist Sun 50 ft 20 ft
` Ponderosa Pine Attracts wildlife and birds.
1$ �� Evergreen.
'1g _ -
L.
hss.� Graceful delicate needles.
s Tsuga heterophylla
Western Hemlock
Dry to Moist Sun to Shade 120 to 200 ft 35 ft Attracts wildlife and birds.
P oil,. Evergreen.
' 414' �' r '' ----
APPENDIX D OPERATIONS & MAINTENANCE TEMPLATE
Date:
Building Permit#or Land-Use Case: Owner Name:
Tax Lot Number:
Owner Address,if different:
Nearest Address:
Stormwater Descriptive Drainage Type
Facility Location (roof,driveway, parking lot,etc.) Impervious Area Treated
Total Impervious Area
Stormwater
Facility Season Maintenance
141
APPENDIX E SIMPLE EROSION AND SEDIMENT CONTROL
TEMPLATE
ESC Site Plan Checklist
For landscaping projects,or projects between 500-1000sf of disturbed soil,applicants may submit a
simple site plan for erosion and sediment control.The following elements must be clearly shown on
the site plan.
•Property Address
•Contractor Name and Emergency Contact Information
•Sediment fencing location
•Concrete washout location (if concrete work involved)
•Inlet protection location(first catch basin within 200ft downstream of property)
•Material stockpile location
•Construction entrance and parking location (existing driveway or gravel pad)
•Clearly mark boundary of disturbed area
Additional items may be required based on project scope of work,or other permit requirements
from Building or Planning.Some items listed above may not be applicable to all projects,these are
minimum requirements. Projects are evaluated on a case-by-case basis,and communication is key
to formulating an effective erosion control plan.
Any questions or concerns may be directed to erosioncontrol@lakeoswego.city.
142
Key
Sediment fence
4
4
Direction of
.A7,-'17->
surface flow 4
ey st\r.9
Shed
S\n9\e e
EX6strr9Res\ileac
F amry
././
Concrete
Washout
Material y
Stockpile
7rea o f stcoctror` \ location /
w as GO e \ //
c ar°
°r/r r6o'b,�g EreXrsdr<g
0S0 drWe`fla-
Type 3 (witch's hat) d
inlet protection in oC Roa
downstream catch 1\160-0
basin
John Doe Construction LLC 1234 Neighbor Road
Lake Oswego, OR
Sheet Al ESC Site Plan (SAMPLE) 97035
Example - Simple Erosion and Sediment Control Plan
-143"'