Controlling Stormwater
Quality and Quantity using
Low Impact
Development
Integrated
Management Practices
[presenters name]
[presentation date]
Outline
Why do we need to control
stormwater quality & quantity?
Low Impact Development
Integrated Management
Practices
● What are they?
● Why use them?
How does this affect
development project review?
Controlling Stormwater Quality
 Urban runoff
is the main
source of
pollutants to
streams and
the Bay.
 Regional Water Quality Control
Board “C.3” permit provisions require
[City/Town] to make stormwater
treatment a condition of approval.
Controlling
Peak Flows & Durations
 Increased runoff
from impervious
surfaces can
accelerate
stream erosion.
 “C.3” requires [City/Town] to limit
runoff from new developments to preproject flows and durations, where
increased runoff could accelerate
stream erosion.
These projects must comply
Threshold
Requirement
Date*
One acre
or more
(impervious
area created
or replaced)
10,000 square
feet or more
Treat runoff 2/15/05
Control
peak flows 10/12/06
& durations
Treat runoff 8/15/06
*development applications deemed complete after this date
Low Impact Development
 Design the
site to mimic
natural
drainage.
 Disperse
runoff to
landscape
where possible.
 Use Integrated Management
Practices distributed around the site.
Example of an engineered
Integrated Management Practice
 “Dry” swale detains and filters runoff
Fitting IMPs into landscaping
Portland, Oregon
Albany, California
Fitting IMPs into landscaping
Seattle, Washington
Spokane, Washington
Planter Box
Reservoir,
12" min. depth
Reverse bend
trap or hooded
overflow
Building
exterior wall
Downspout
Cobbles or
splash block
18" sandy loam,
minimum
infiltration rate
5" per hour
Filter fabric
Concrete or other
structural planter wall with
waterproof membrane
12" open-graded
gravel, approx.
½" dia.
Perforated pipe
Additional
waterproofing on
building as
needed
Drain to storm drain or discharge;
bottom-out or side-out options
Planter Box
Integrated Management Practices
Advantages
Challenges
 Detain and treat
runoff
 Typically fit into
setbacks and
landscaped areas
 Accommodate
diverse plant
palettes
 Low-maintenance
 Don’t breed
mosquitoes
 Can be attractive
 Soil surface must
be 6-12" lower
than surrounding
pavement
 Require 3-4 feet of
vertical “head”
 Can affect
decisions about
placement of
buildings,
roadways, and
parking
Development Review
 IMPs can be
effective,
attractive, and
accepted by
developers
 Incorporate IMPs
in preliminary
site, landscaping
and drainage
design drawings
In-ground planter boxes
under construction
Residential subdivision
Clayton, May 2006
Maintenance of IMPs
 Prior to planning & zoning approval
● Identify maintenance requirements
● Identify maintenance responsibility
 Typical maintenance requirements
● Check inlets and outlets
● Irrigate and maintain plantings
 [City/Town] must either
● Accept maintenance responsibility or
● Legally assign it to property owner(s)
 [City/Town] reports inspection results to
Water Board annually
Implementation
 [City/town] ordinance requires a
design exhibit and a report with
planning and zoning application
 Contra Costa Clean Water Program
Stormwater C.3 Guidebook explains
how to prepare the submittal
 Staff works with applicant to
integrate IMPs into the project