Low Impact Development
Eastern Washington
Guidance Manual
prepared by:
june 2013
THIS PAGE INTENTIONALLY LEFT BLANK
Acknowledgements
AUTHORS:
Wayne Carlson, AHBL, Inc.
Erick Fitzpatrick, AHBL, Inc.
Emily Flanagan, HDR Engineering
Robin Kirschbaum, HDR Engineering
Holly Williams, AHBL, Inc.
Len Zickler, AHBL, Inc.
DESIGN & LAYOUT:
Holly Williams, AHBL, Inc.
PROJECT MANAGER:
Russ Connole, Spokane County
PRIMARY GRANT PARTNER:
Tanyalee Erwin, Washington Stormwater Center
ECOLOGY PROJECT MANAGER:
Douglas Howie
ECOLOGY CONTRIBUTORS:
Dave Duncan, Eastern Region
Terry Wittmeier, Central Region
EASTERN WASHINGTON GRANT PARTNERS:
Asotin County
City of Ellensburg
City of Kennewick
City of Moses Lake
City of Pasco
City of Pullman
City of Richland
City of Spokane Valley
City of Walla Walla
City of Wenatchee
City of West Richland
Washington State University
LOW IMPACT DEVELOPMENT – STAKEHOLDER ADVISORY GROUP:
Nancy Aldrich, City of Richland
Rob Buchert, City of Pullman
Marcia Davis, City of Spokane
Jason Detamore, Chelan County
Jennifer Lange, Douglas County
Gloria Mantz, City of Spokane Valley
Jon Morrow, City of Ellensburg
Martin Nelson, City of Kennewick
Gene Patterson, Washington State University
Michelle Perdue, City of Moses Lake
Teresa Reed-Jennings, City of Pasco
Lynn Schmidt, City of Spokane
Jessica Shaw, City of Wenatchee
Cheryl Sonnen, Asotin County
Shilo Sprouse, City of Pullman
Bryan Woodard, City of West Richland
Matt Zarecor, Spokane County
LOW IMPACT DEVELOPMENT – TECHNICAL REVIEW COMMITTEE:
Ben Brattebo, Spokane County
Doug Busko, CH2MHill
Brian Cochrane, Yakima County
Alice Lancaster, Herrera Environmental Consultants
Jim Lenhart, Stormwater Northwest
Aimee Navickis-Brasch, University of Idaho
Scott Rivas, DCI Engineers
Joe Simmler, PACE Engineers
Chris Webb, Maul Foster & Alongi
FUNDING:
Washington State Department of Ecology
THIS PAGE INTENTIONALLY LEFT BLANK
PREFACE
Foreward……………………………………………………………………………………………………………………………………………i
Manual Organization………………………………………………………………………………………………………………………………..iii
Acknowledgements…………………………………………………………………………………………………………………………………….iii
CHAPTER 1: INTRODUCTION……………………………………………………………………………………………………………..1
1.1
Eastern Washington Hydrology & Climate…………………………………………………………………………………………1
1.2
Effects of Urbanization………………………………………………………………………………………………………………….3
1.3
LID & the Eastern Washington NPDES Municipal Stormwater Permit……………………………………………………6
1.4
Hard Engineering & Soft Engineering – Toward an LID Approach……………………………………………………….7
1.5
LID in Eastern Washington…………………………………………………………………………………………………………..10
CHAPTER 2: PLANNING FOR LID………………………………………………………………………………………………………13
2.1
Introduction………………………………………………………………………………………………………………………13
2.2
LID Planning Principles………………………………………………………………………………………………………………..14
2.3
Site Analysis……………………………………………………………………………………………………………………………….14
2.4
Site Mapping Process………………………………………………………………………………………………………………….21
CHAPTER 3: DESIGNING FOR LID…………………………………………………………………………………………………..23
3.1
Design Process Overview…………………………………………………………………………………………………………….23
3.2
Steps for Design of Infiltration Facilities…………………………………………………………………………………………26
3.3
Residential Design Strategies……………………………………………………………………………………………………….27
3.4
Commercial & Industrial Design Strategies………………………………………………………………………………………37
CHAPTER 4: LID BMPS…………………………………………………………………………………………………………………..41
4.1
Introduction…………………………………………………………………………………………………………………………41
4.2
Amending Construction Site Soils…………………………………………………………………………………………………43
4.3
Dispersion………………………………………………………………………………………………………………………49
4.4
Bioretention………………………………………………………………………………………………………………………55
4.5
Trees……………………………………………………………………………………………………………………………………..93
4.6
Permeable Pavement………………………………………………………………………………………………………………..103
4.7
Vegetated Roofs……………………………………………………………………………………………………………………….137
4.8
Minimal Excavation Foundations………………………………………………………………………………………………….145
4.9
Rain Water Harvesting……………………………………………………………………………………………………………….153
TABLE OF CONTENTS
APPENDICES
Appendix A:
Glossary………………………………………………………………………………………………………………………163
Appendix B:
Evaluating Soil Infiltration Rates……………………………………………………………………………………….169
Appendix C:
Sizing of LID Facilities…………………………………………………………………………………………………….173
Appendix D:
Bioretention Plant List……………………………………………………………………………………………………185
Appendix E:
Detail Drawings…………………………………………………………………………………………………………….203
Appendix F:
LID Planning and Design Checklist…………………………………………………………………………………..215
Appendix G:
Maintenance of LID Facilities…………………………………………………………………………………………..221
Appendix H:
References…………………………………………………………………………………………………………………..233
Preface
Foreward
Low Impact Development (LID) is an approach to land
development (or re-development) that works with nature
to manage stormwater as close to its source as possible.
LID employs principles such as preserving and recreating
natural
landscape
features,
minimizing
effective
imperviousness to create functional and appealing site
drainage that treat stormwater as a resource rather
than a waste product. There are many practices that
have been used to adhere to these principles such as
bioretention facilities, rain gardens, vegetated rooftops,
rain barrels, and permeable pavements. By implementing
LID principles and practices, water can be managed in a
way that reduces the impact of built areas and promotes
the natural movement of water within an ecosystem
or watershed. Employed on a broad scale, LID can
help maintain or restore a watershed’s hydrologic and
ecological functions.
Typical applications of LID include new development,
redevelopment, and retrofits to existing development.
LID has been adapted to a range of land uses from high
density urban settings to low density development (EPA
2013), and has been demonstrated to work in arid and
semi-arid regions such as eastern Washington.
The purpose of this Manual is to provide stormwater
managers, site designers, and design reviewers with
a common understanding of LID goals, objectives,
design of individual practices, and flow reduction and
water quality treatment that are applicable to eastern
Washington. LID is a constantly evolving stormwater
management approach. Over time, new technologies
and best management practices (BMPs) will promote
greater efficiency in managing stormwater runoff. This
document will evolve as additional research becomes
available,
new
and
innovative
practices
become
approved for general use, and professionals in the
region gain more practical experience. The Washington
Stormwater Center (WSC) will be cataloging LID research
and new and emerging tools that are relevant to eastern
Washington practitioners and publishing it on its website
(www.wastormwatercenter.org).
Unless adopted through a locally-enacted ordinance,
the Manual is intended to provide guidance to assist
professional designers and does not replace or supersede
local design standards or requirements.
Preface
AMENDING
CONSTRUCTION
SITE SOILS
TREES
MINIMAL
EXCAVATION
FOUNDATIONS
DISPERSION
BIORETENTION
PERMEABLE
PAVEMENT
RAIN WATER
HARVESTING
VEGETATED
ROOFS
AHBL, Inc.
City of Spokane
AHBL, Inc.
HDR Engineering
NAC Architecture
AHBL, Inc.
CleanWater Services
Preface
iii
Manual Organization
This Manual consists of 4 chapters. Chapter 1
(Introduction) sets the context for the LID approach
with an introduction to eastern Washington climate and
hydrology and the effects of urban development on water
resources. Chapter 1 also establishes the goals and
objectives for LID in the context of the reissued Eastern
Washington Phase II NPDES Municipal Stormwater
General Permit.
Chapter 2 (Planning for LID) describes the LID planning
principles, site analysis, site inspection, and composite
map that form the foundation for an LID design. Chapter
3 (Designing for LID) builds on the planning and site
map development and provides guidance for site
design. Chapter 4 (LID BMPs) provides design guidance
describing the use, applications and limitations, design
factors, maintenance, and construction considerations
associated with the design of the following BMPs:
Amending construction site soils.
Dispersion.
Bioretention, infiltration planters and flow-
through planters.
Trees.
Permeable pavement.
Vegetated roofs.
Minimal excavation foundations.
Rain water harvesting.
Appendices include:
Appendix A: Glossary.
Appendix B: Evaluating Soil Infiltration Rates.
Appendix C: Sizing of LID Facilities.
Appendix D: Bioretention Plant List.
Appendix E: Detail Drawings.
Appendix F: LID Planning and Design Checklist.
Appendix G: Maintenance of LID Facilities.
Appendix H: References.
Acknowledgements
This Manual is a collaborative product of Spokane
County, the Washington State Department of Ecology
(Ecology), the Washington Stormwater Center (WSC),
Washington State University (WSU), and the Eastern
Washington Phase II Municipal Stormwater Permittees.
Funding for this project was provided by Ecology. Figure
A depicts the six county and 18 city Permittees.
Preface
FIGURE A
Eastern Washington and NPDES Municipal Stormwater General Permit Areas
Source: AHBL, Inc.
Introduction
In this chapter:
Eastern Washington Hydrology & Climate 1.1
Effects of Urbanization 1.2
LID & the Eastern Washington NPDES Municipal Stormwater Permit 1.3
Hard Engineering & Soft Engineering – Toward an LID Approach 1.4
LID in Eastern Washington 1.5
chapter1.0
Introduction
1.1 Eastern Washington
Hydrology & Climate
The landscape of eastern Washington is varied and
includes prairies, pine forests, the shrub-steppe,
channeled scablands, and vast areas of irrigated and dry
land agriculture. Likewise, the hydrology and climate of
eastern Washington also vary considerably.
Hydrology in eastern Washington is highly influenced by
landscape, topography, and precipitation. Across the
region, much of the winter precipitation falls as snow
which does not melt until warmer temperatures of spring
cause high-runoff to occur from April through June. By
July, most of the mountain snow has melted and the
streamflow becomes low (USGS, 2013). Seasonal
irrigation and dams have altered the natural hydrology
of some streams.
The 2004 Ecology Stormwater Management Manual for
Eastern Washington (2004 SWMMEW) has classified
eastern Washington into four climate regions (Ecology,
2004). Figure 1.1 depicts the four climatic regions which
include: East Slopes of Cascade Mountains (Region
1); Central Basin (Region 2); Okanogan, Spokane,
Palouse (Region 3); and Northeastern Mountains and
Blue Mountains (Region 4). The following text provides
discussion of the precipitation patterns in each region.
Chapter One
FIGURE 1.1 – EASTERN WASHINGTON CLIMATE REGIONS
Approximate eastern Washington climate regions.
Source: Ecology Stormwater Management Manual for Eastern Washington (2004) and AHBL, Inc.
olu
River
n R
Metho
Pal
e R
Snak
12.5
Miles
195
395
Ellensburg
Yakima
Spokane
Walla Walla
Pasco
Kennewick
Richland
Moses
Lake
Wenatchee
Ellensburg Valley
Yakima
Valley
Selkirk
Mountains
Blue
Mountains
Palouse
Saddle
Mountains
Winthrop
Okanogan
Columbia River
Pullman
Colville
Chelan
1.1.1 Eastern Washington
Climate Regions
REGION 1 – EAST SLOPES OF CASCADE MOUNTAINS:
This region is comprised of mountain areas on the east
slopes of the Cascade Mountains. It is bounded to the
west by the Cascade crest and generally bounded to
the east by the contour line of 16 inches average annual
precipitation.
Precipitation in this region diminishes as the distance
from the summit increases and the elevation decreases.
For example, within a distance of 20 miles, the average
annual precipitation decreases from 92 inches at
Stampede pass (elevation 3,958 ft.) to 22 inches at Cle
Elum (elevation 1,920 ft.). The average winter season
snowfall decreases from approximately 400 inches
near the summit of the mountains to approximately
75 inches at 2,000 feet above sea level.
REGION 2 – CENTRAL BASIN: This region is comprised
of the Columbia Basin and adjacent low elevation areas in
central Washington. It is generally bounded to…