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Natural
Approaches to Stormwater Management
Ordinances
& regulations
Island
County Stormwater Code
Low Impact Development Requirements
Background
In
December 1998, Island County adopted a stormwater ordinance that
provides developers with the option of using low impact development
practices. The design standards are based on Low Impact Development
Design Strategies—An Integrated Design Approach, prepared by
Prince Georges County, Maryland, January 2000.
Description
The
Island County Stormwater and Surface Water Ordinance provides special
performance requirements that developers must meet for their development
proposals to qualify as LID. The code states:
A.
Runoff Volume Control.
The pre-development volume is maintained by a combination of minimizing
the site disturbance from the pre-development to the post development
condition and then providing distributed retention BMPs. Retention
BMPs are structures that retain the runoff for the design storm
event. A “customized” or detailed runoff curve number (CN) evaluation
is required to determine the required runoff volume. The storage
required to maintain the pre-development volume may also be sufficient
to maintain the pre-development peak rate.
B.
Peak Runoff Rate Control. Low-impact development is designed
to maintain the pre-development peak runoff discharge rate for
the selected design storm events. This is done by maintaining
the pre-development time of concentration and then using retention
and/or detention BMPs (e.g., rain gardens, open drainage systems,
etc.) that are distributed throughout the site. The goal is to
use retention practices to control runoff volume and, if these
retention practices are not sufficient to control the peak runoff
rate, to use additional detention practices to control the peak
runoff rate.
C.
Flow Frequency Duration Control. Since low-impact development
is designed to emulate the pre-development hydrologic regime through
both volume and peak runoff rate controls, the flow frequency
and duration for the post development conditions will be almost
identical to those for the pre-development conditions. The impacts
on the sediment and erosion and stream habitat potential at downstream
reaches can then be minimized.
D.
Water Quality Control. Low-impact development is designed
to provide water quality treatment control for the duration storm
runoff from impervious areas using retention practices. The storage
required for water quality control is compared to the storage
required to control the increased runoff volume. The greater of
the two volumes is the required retention storage. Low-impact
development also provides pollution prevention by modifying human
activities to reduce the introduction of pollutants into the environment.
(Title 11.03)
The
ordinance allows applicants who propose to use LID practices for
development approvals a choice. Applicants of small development
projects may accept permit conditions that fulfill the best management
practices for LID surface water rate control in lieu of submitting
a drainage narrative. For major development activities and engineered
grading projects, applicants who propose to use LID drainage controls
may submit a drainage narrative instead of a preliminary drainage
plan. The ordinance does not require a downstream analysis when
the project design includes and is approved for using LID standards.
To
date, LID practices have been partially applied in developments
such as Bayview Corner (see page 26), but no major developments
have used LID technologies in Island County.
Contact
Phil
Cohen
Surface
Water Management Division
Island County Public Works
Phone:
(360) 679-7331 extension 7440
FAX:
(360) 678-4550
philc@co.island.wa.us
Stormwater
Management Policy
for Low Impact Development
City of Issaquah
Background
The
city of Issaquah is growing rapidly. With annexations, the population
could increase from 13,790 today to 47,000 by 2020. Two urban villages
alone—Issaquah Highlands and Talus—could add more than 5,000 residential
units, 3.5 million square feet of commercial and office space and
500,000 square feet of retail space. This growth will place heavy
demands on already limited groundwater supplies, a congested road
system and degraded stream ecosystems. Issaquah Creek is a regionally
significant stream that provides habitat for the threatened Puget
Sound chinook salmon. In 2000, the city of Issaquah adopted an update
to the stormwater code (Title 13.28.055) that provides a process
and criteria for evaluating low impact development proposals.
Description
The
municipal code authorizes the Director of Public Works to authorize
deviations from stormwater design standards to achieve “low impervious
surface development.” The director also has the option of requiring
evaluation and monitoring of project elements. The code language
is on the Municipal Research Services Center website (www.mrsc.org).
Go to “Legal Resources,” then “City and County Codes,” then “City
Codes” to Issaquah City Code Title 13.28.055.
Authorizations
for deviation from design standards are to be based on the following
criteria. The policy states:
1. The deviations
will produce a compensating or comparable result in stormwater
flow control and treatment that is in the public interest;
2. The deviations contribute to and are consistent with the goal
of achieving low effective impervious surface area within a development;
3. The proposed development project offers reasonable assurances
that low impervious surfaces will be achieved and maintained;
4. The deviations do not threaten public health or safety;
5. The deviations are consistent with generally accepted engineering
and design practices;
6. The deviations promote one or more of the following:
a. Innovative site or housing design;
b. Increased on-site stormwater retention using native vegetation;
c. Retention of at least 60 percent of natural vegetation conditions
over the site;
d. Improved on-site water quality beyond that required by current
applicable regulations;
e. Retention or re-creation of pre-development and/or natural
hydrologic conditions to the maximum extent possible;
f. The reduction of effective impervious surfaces to the maximum
extent practicable;
7. The deviations do not allow density greater than what would
otherwise be allowed under city regulations then in effect;
8. The deviations do not present significantly greater maintenance
requirements at facilities that will be eventually transferred
to public ownership;
9. There shall be submitted in conjunction with each such project,
covenants, conditions and restrictions which will be binding upon
the property all necessary native growth protection easements,
impervious surface restrictions and such other critical features
as the Director may require.
The
Issaquah Municipal Code (Title 13.30) also provides an incentive
for projects that infiltrate stormwater. Projects that infiltrate
100 percent of the stormwater can receive up to a 50 percent reduction
in the stormwater utility fee.
On
other fronts, the city is considering a more comprehensive sustainable
development program, including incentives. Some of these provisions
relate directly to LID, such as green streets, green roofs, and
pervious pavers.
Contact
Kerry
Ritland
City
of Issaquah
(425)
837-3410
kerryr@ci.issaquah.wa.us
Zero
Effect Drainage Discharge Ordinance
City
of Lacey
*
Zero Effect (or Impact) Development
(ZID) means a project that adheres to the 60/0 development standard
and is constrained by characteristics of a healthy watershed as
described in the Salmon in the City Conference Abstracts. “60/0”
means 60 percent forest cover preserved /zero effective impervious
surface.
Background
In
1999, the Lacey city council enacted a “Zero Effect* Drainage
Discharge” ordinance. Lacey, in Thurston County, has a population
of 31,000 and an urban growth area of 31 square miles. City officials,
understanding that even small increases in runoff can damage area
streams, chose to encourage developers to achieve zero discharge
of stormwater runoff. This could well be one of the very first ordinances
of this kind passed in the nation.
Description
The
goal of Lacey’s ordinance is to retain the critical functions of
a forest including evapotranspiration and infiltration after site
development such that near zero effective impervious surface is
achieved. The purposes of the ordinance show that city planners
saw this as a new concept that would go through trial and evolution.
The ordinance states:
A.
Provide those developing land the opportunity to demonstrate zero
effective impervious surfaces.
B. Improve the conditions of habitat and ground and surface waters
within a watershed with innovative urban residential design and
development techniques.
C. Foster broad community acceptance of the use of significantly
less impervious surface and greater natural habitat conservation
on sites.
D. Provide the opportunity to identify and evaluate potential
substantive changes to land use development regulations which
support and improve natural functions of watersheds.
The ordinance is flexible and establishes performance standards
for development rather than specific design criteria. A committee
of Lacey staff has the authority to grant administrative variances
from traditional standards to achieve the ordinance’s goal.
Projects
must preserve 60 percent natural habitat area and achieve “near
zero effective impervious surface.” A variety of practices can contribute
to meeting the provisions of the ordinance, such as:
- Constructing
narrower roads without curb and gutter.
- Using
pervious paving systems.
- Using
native forest as the stormwater management system.
- Avoiding
discharges from impervious surfaces to surface streams.
Expected
Results
The
intent of the ordinance is that projects constructed under this
ordinance will eliminate overland flow discharges and have no measurable
impact on receiving waters and aquatic life. Such projects will
be more aesthetically pleasing, require little or no erosion control
during construction, and add value to the city.
Contacts
Eric
Hielema
City
of Lacey
(360)
438-2686
ehielema@ci.lacey.wa.us
Website:
www.wa.gov/lacey/main_menu/main_set.html
Website for Chapter 14.31 Zero Effect Ordinance:
www.wa.gov/lacey/lmc/lmc_main_page.html
Thomas
W. Holz
SCA
Consulting Group
(360)
493-6002
tholz@scaconsultinggroup.com
Low
Impact Development Strategy for Green Cove Basin
City
Of Olympia
Background
Olympia,
with a population of 41,000, is a rapidly growing city in Thurston
County. Despite a variety of measures enacted in the 1980s and 1990s
to increase density and protect environmental quality, the quality
and diversity of aquatic habitat in the city continued to decline.
In 1998, Olympia undertook a process to “define the balance between
human activities and protecting habitat” in its streams and watersheds.
After reviewing all city watersheds, the city council decided to
focus on the 2,600-acre Green Cove Creek watershed in west Olympia.
In October 2001 the Olympia City Council adopted a unique set of
mandatory low impact development regulations to prevent further
damage to aquatic habitat from urban development in the Green Cove
Basin.
Description
Olympia
elected officials and staff went through a three-year process of
research, analysis and peer review in designing the program for
Green Cove Basin. Following is a summary of the major steps:
- Consultants
developed criteria for evaluating the viability of aquatic habitat
in Olympia’s eight watersheds and recommended goals for growth
and habitat based on the habitat potential of each basin.
- A
team of scientists, including hydrologists and biologists, reviewed
and concurred with the consultant’s recommendations.
- The
city council agreed to use the recommended approach in the Green
Cove Basin as a pilot project and adopted interim standards for
zoning density, stormwater management, timing of clearing and
grading, and tree removal.
- Consultants
developed alternate site plans for two proposed developments in
the basin to determine whether they could achieve low impact objectives.
The city also consulted with realtors, development engineers,
bankers, and developers on the site plans.
- The
science team reviewed the standards and proposed designs and confirmed
that the proposed subdivision designs were generally consistent
with scientific findings and that implementation would have the
potential to maintain habitat conditions equivalent to the present.
Based on the above process, the Olympia City Council completed a
comprehensive policy revision covering development density, impervious
surface coverage, lot size, open space/tree retention, street design,
street width, block sizes, parking, sidewalks, and stormwater management
requirements. The following is an outline of key policy changes
for the Green Cove Basin.
Comprehensive
Plan Amendments
- Designate
Green Cove Creek as a sensitive drainage basin.
- Avoid
high-density development where new development would have a significant
adverse impact upon the habitat within designated sensitive drainage
basins.
- Administer
development regulations that protect critical areas and designated
sensitive drainage basins.
- Adopt
low impact development regulations within designated sensitive
drainage basins that may include stormwater standards, critical
area regulations, zoning designations and other development standards.
- Establish
street designs that minimize impacts to the natural environment
especially within a designated sensitive drainage basin.
Olympia
Municipal Code
- Establish
a new zoning district with increased tree protection and replacement
requirements.
- Establish
residential densities of two to four units per acre; allow duplexes,
townhouses, and multifamily uses.
- Reduce
lot widths and rear setbacks and increase maximum building heights
compared to other residential districts.
- Limit
maximum impervious surface coverage per lot to 2,500 square feet.
- Allow
several land uses, including duplexes and parking lots that are
not typically permitted in single-family residential developments.
- Require
a minimum tree density of 220 trees per acre (approximately 55
percent tree cover in any given development).
Development
Guidelines and Public Works Standards
- Residential
block perimeters cannot exceed 1,700 feet.
- Driveways
and sidewalks can be constructed of pervious surfaces with city
approval.
- Sidewalks
are required on one side of local access streets.
- Sidewalk
planter widths can be increased from the required eight feet to
an optional 25 feet.
- Additional
parking within low impact developments can be provided by the
construction of pervious surface lots subject to city approval.
- A
rock infiltration gallery/conveyance system is to be constructed
when street slopes are 5 percent or less.
- Neighborhood
collector streets are to be 25 feet wide, with parking provided
on alternating sides of the street.
- Local
access streets are to be 18 feet wide, with similar parking arrangements.
Drainage
Design and Erosion Control Manual
- Stormwater
discharge must be controlled by matching developed discharge durations
to pre-developed durations, for the range of pre-developed discharge
rates from 50 percent of the two-year peak flow to the 50-year
peak flow.
- The
city will allow clearing and grading within the basin only between
May 1 and October 1 of any given year.
Since part of the Green Cove Basin is in Thurston County, the county
adopted policy and regulatory changes to complement Olympia’s program.
This included changes to the county’s comprehensive plan, zoning,
and open space program.
Unlike
LID ordinances in Lacey and Tumwater that are voluntary, Olympia’s
Green Cove regulations are mandatory. As of October 2002, the city
has received two subdivision projects for development under the
new policies.
Challenges
Several
questions remain unresolved in the Green Cove basin process. The
extra costs of non-standard development techniques have not been
defined. One question is whether home buyers will buy homes in a
“low impact” neighborhood with narrower streets, less parking, smaller
home footprints, and regulatory limits to additions that would increase
impervious surfaces. Finally, there are still questions about the
environmental benefits of the development restrictions, given the
overall pattern of development and previous disruption of the natural
hydrology.
Contact
Andy
Haub
City
of Olympia Public Works
(360)
753-8475
ahaub@ci.olympia.wa.us
For a more detailed case study and a CD-ROM containing project reports
and ordinances, contact the City of Olympia.
Low
Impact Development Regulations
Pierce
County
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Select
photo to view in larger scale
Example of a site design using LID techniques. |
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Background
Unincorporated
Pierce County has a population of 330,000 and a land area of 1,790
square miles. The county is exploring the use of low impact development
techniques as a method to maintain natural hydrologic functions
during the land development process and reduce impacts associated
with conventional stormwater management methods. County staff is
evaluating various LID methods for quality of performance and applicability.
Development of an LID chapter within the county’s Stormwater and
Site Development Regulations will clarify what LID techniques are
acceptable and will establish a performance goal and objectives.
This chapter will also provide certainty to land developers and
federal and state agencies in terms of performance measures and
compliance with National Pollutant Discharge Elimination System
requirements.
Description
Pierce
County, in cooperation with Washington State University Cooperative
Extension, is currently developing an LID chapter for the Stormwater
Management and Site Development Regulations. A committee review
of the proposal was underway at the time of this writing in late
2002.
The following draft chapter establishes a performance goal and objectives
and prescriptive standards for LID.
The goal of
Low Impact Development is to manage stormwater generated from
new development and redevelopment so there will be no negative
impacts to adjacent and/or downstream property owners and no degradation
to groundwater or surface waters such as but not limited to streams,
ravines, wetlands, potholes, and rivers.
The Low Impact Development goal shall be achieved
through adherence to the following objectives:
- Maintain
and/or restore the pre-developed, undisturbed stormwater flow
volumes, flow frequencies and durations, and water quality from
a developed site. In the Puget Sound lowlands, the predeveloped
hydrologic condition is near zero overland flow runoff. (Note:
To provide a quantifiable and measurable standard for flow control,
minimum requirement #7 Flow Control of the Department of Ecology
Stormwater Management Manual for Western Washington, will
be adhered to in addition to meeting the other objectives listed
below. It states that stormwater discharges shall match developed
discharge durations to predeveloped durations for the range
of predeveloped discharge rates from 50% of the 2-year peak
flow up to the full 50 year peak flow.)
- Establish
the pre-developed condition of a site used for hydrologic modeling
as the native vegetation and soils that existed on the site
prior to 1800 A.D., which shall be a forested land cover unless
reasonable, historic information indicates the site was prairie
prior to settlement (modeled as “pasture” in the Western Washington
Hydrology Model.)
- Retain
or restore native soils and vegetation on 65% of the site area.
Where 65% is not achieved the applicant will demonstrate how
the combined use of other LID techniques will achieve the overall
goal.
- Limit
the effective impervious area of the site to no more than 10%.
- Retain
and incorporate natural site features that promote infiltration
of stormwater on a developed site.
- The
use of traditional conveyance and pond technologies to manage
stormwater quality and quantity should only be considered after
all other LID techniques have been considered and used to the
greatest extent possible.
- Use
bioretention, pervious surfaces, open space surface water dispersion,
soil restoration, and other dispersed facilities to control
stormwater as close to the origin as possible.
To meet the goal and objectives, the draft chapter discusses how
LID can be considered at each phase of development including: site
planning; vegetation retention and reforestation; site clearing
and grading; roads, parking and sidewalks; and building design.
It also provides best management practices and monitoring requirements.
In addition, the chapter will address ongoing management and maintenance
needs, and education of homeowners.
Pierce County, in cooperation with Washington State Cooperative
Extension, has entered into a partnership with a private developer
to develop an LID pilot project. For more information on this project,
see Meadow on the Hylebos, page 32, or call Len Zickler, AHBL, at
(253) 383-2422.
Contacts
Katherine
Brooks
Pierce
County, Planning & Land Services
(253)
798-3181
kbrooks@co.pierce.wa.us
Hans
Hunger
Pierce
County Public Works and Utilities Water Programs
(253)
798-6162
hhunger@co.pierce.wa.us
Website:
www.co.pierce.wa.us/pc/services/home/property/pals/landuse/esa.htm
(see Title 17A amendments)
Reduced
Discharge Housing Demonstration Program
Snohomish
County
Background
In
the 1990s, Snohomish County, with a population of 628,000, established
a program to introduce different development schemes, such as mixed
use, affordable housing and innovative designs. As part of this
effort, the county adopted the Reduced Discharge Housing Demonstration
Program (Ordinance 00-004) in April 2000. This program provides
a three-year trial period for selecting and overseeing demonstration
low impact development projects.
Description
The
reduced discharge ordinance has five purposes:
-
Demonstrate the benefits of alternative development practices
that reduce offsite discharge.
- Improve
the conditions of habitat, ground and surface waters.
- Foster
community acceptance of housing that conserves habitat and uses
less impervious surface.
- Allow
flexibility in the development standards.
- Identify
and evaluate desirable changes to the land use code.
Requirements
and guidelines in the ordinance provide for a variety of LID concepts,
such as infiltration, tree retention, density bonuses, smaller footprints/taller
house designs, permeable pavements, grass pavers, and minimizing
grading and site disturbance.
The
county established a special committee to oversee the program, select
demonstration sites and recommend changes to the land use code.
The committee includes representatives of county departments, environmental
organizations, university faculty, and the development community.
The committee began its work with a tour of low and reduced impact
development sites in Snohomish and King counties. Snohomish County
sites included the Canyon Park Business Center (which uses bioswales
for water quality treatment and groundwater recharge) and the Harbor
Point Master Planned Community (which recharges groundwater through
a wetland).
To guide submittal of development proposals, the committee developed
an outline of minimum requirements and a project review checklist
(available from the county on request). By the end of 2002, developers
had proposed six project design concepts. The county accepted three
of these projects into the system. The project rating system evaluates
tree retention (minimum 60 percent of the site); impervious surfaces;
infiltration (minimum 70 percent); visual impact; innovation; and
the reputation of the developer.
One
project proposal is for higher-end fourplex condominiums. The site
is heavily forested with steep slopes and outwash soils. A vertical
design with underground parking and narrower roads will save tree
cover and reduce runoff. Permeable pavement will reduce impervious
cover and soils will be amended with compost. The county will need
to modify the zoning code from the current single-family classification
to allow for this type of development in this area.
The
second proposal, Wandering Creek, is for lower cost single-family
housing. The site is bounded by wetlands on three sides. The upland
area is on outwash soils and will drain to a wetland buffer. LID
features include preserving overstory vegetation, working with topography,
narrowing the road section, using permeable pavers, and reducing
building footprints to 1,000 square feet.
A
third proposal is in an existing plat where the developer proposes
to revegetate a pasture area with trees.
County
staff and the developers will jointly monitor each of the development
projects for stormwater flows. Results will be available to the
public once construction begins.
Challenges
The
county’s demonstration program has faced several challenges in implementation.
Developers and engineers have proven reluctant to try new approaches
and techniques. They also state that the Department of Ecology’s
Stormwater Management Manual for Western Washington limits
the use of wetlands for infiltration.
Costs
Cost
estimates for these LID projects are highly variable and site-dependent.
The fourplex project on a steep slope will be expensive due to the
vertical design and underground parking, but the site would be difficult
to develop without the flexibility provided under the LID program.
The single-family housing project is expected to be less expensive
than a traditional development because of reduced road width and
sidewalks on one side of roads. The developer is also receiving
a density bonus, which allows him to add several housing units on
the site.
Contact
Randy
Sleight
Snohomish
County Planning and Development Services
(425)
388-3424 extension 2014
randy.sleight@co.snohomish.wa.us
Zero
Effect Development Ordinance
City
of Tumwater
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*Zero
Impact Development means a project
that adheres to the 65/0 (65 percent forest cover preserved
/ zero effective impervious surface) development standard and
is constrained by characteristics of a healthy watershed as
described in the Salmon in the City Conference Abstracts. |
| |
Background
The city of Tumwater in Thurston County has a population of
12,730 and an area of 10.7 square miles. Several years ago, city
officials and staff recognized the relationship between traditional
development practices and stream degradation, and established alternative
development standards to protect aquatic life in receiving waters.
Description
In
2000, Tumwater enacted the Zero Effect Drainage Ordinance (Title
13, Chapter 13.22). The city found that typical site development
hinders stormwater retention, that stormwater discharges offsite
adversely affect stream habitat, and that retaining forest canopy
aids evapotranspiration and infiltration of stormwater runoff. The
ordinance provides developers with the option of using zero impact
development* practices in residential and commercial projects. A
set of performance guidelines indicates the characteristics of an
acceptable project.
While
the ordinance contains design guidance it also allows design creativity.
A committee reviews project proposals and can approve variances
to the city’s development code to accommodate nontraditional construction
techniques. Projects approved under the ordinance must preserve
65 percent of forest area on the development site. Runoff must not
be collected or discharged to surface water (thus achieving zero
effective impervious area). The guidelines encourage looped one-way
streets; narrow pervious driveways; small, pervious garage aprons;
and small home footprints. Roof runoff must be infiltrated or mitigated.
To compensate for narrower roads and reduced access for emergency
vehicles, structures are required to meet more rigorous fire standards.
Costs
There
is the potential for substantial cost savings for projects that
might be approved under this ordinance, however no cost analysis
was performed.
Contacts
Michael
Matlock
City
of Tumwater
(360)
754-4210
Website:
www.ci.tumwater.wa.us/
Follow
the link to City Departments,
then Planning and Facilities.
Thomas
W. Holz
SCA
Consulting Group
(360)
493-6002
tholz@scaconsultinggroup.com
Low
Impact Development in the Highway Runoff Manual
Washington
State Department of Transportation
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Select
photo to view in larger scale
Workers
install Eco-Stone® permeable pavers at a municipal park and
ride in Marysville. The Washington State Department of Transportation
is considering using permeable pavement, such as Eco-Stone®,
at its park and rides and on pedestrian paths. |
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Select
photo to view in larger scale
Eco-stone
detail |
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Description
The Washington State Department of Transportation is currently
revising its 1995 Highway Runoff Manual. As part of this
revision, the department will develop and reference three low impact
development elements in the revised manual:
1. Permeable paving at park and rides, pedestrian paths, and lower
speed roadways.
2. Bioretention along roadways.
3. Constructed wetlands for stormwater treatment.
The
LID portion of the revised manual should be available for use by
the end of September 2003 and will include plans, specifications,
methodology for estimating costs, and a hydraulic design process.
Contacts
Rick Johnson
Washington
State Department of Transportation
(260)
440-4642
johnsor@wsdot.wa.gov
Larry Schaffner
Washington
State Department of Transportation
(360)
570-6657
schaffl@wsdot.wa.gov
Website:
www.wsdot.wa.gov/fasc/
Follow the links to:
>Engineering
Publications
>On-Line
Technical Manual Library
>Highway
Runoff Manua
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