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Low Impact Development
[presenters name][presentation date]
Integrated Management Practices
Controlling Stormwater Quality and Quantity using
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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?
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Controlling Stormwater Quality
Urban runoff is the mainsource ofpollutants tostreams andthe Bay.
Regional Water Quality Control Board “C.3” permit provisions require [City/Town] to make stormwater treatment a condition of approval.
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Increased runofffrom impervioussurfaces canacceleratestream erosion.
“C.3” requires [City/Town] to limit runoff from new developments to pre-project flows and durations, where increased runoff could accelerate stream erosion.
Controlling Peak Flows & Durations
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These projects must complyThreshold Requirement Date*
One acre or more (impervious area created or replaced)
Treat runoff
2/15/05
Control peak flows & durations
10/12/06
10,000 square feet or more
Treat runoff
8/15/06
*development applications deemed complete after this date
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Low Impact Development
Design the site to mimic natural drainage.
Disperse runoff to landscape where possible.
Use Integrated Management Practices distributed around the site.
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Example of an engineered Integrated Management Practice
“Dry” swale detains and filters runoff
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Fitting IMPs into landscaping
Portland, Oregon Albany, California
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Fitting IMPs into landscaping
Seattle, Washington
Spokane, Washington
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Reservoir, 12" min. depth
Reverse bend trap or hooded overflow
18" sandy loam, minimum infiltration rate 5" per hour
12" open-graded gravel, approx. ½" dia.
Perforated pipe
Downspout
Building exterior wall
Cobbles or splash block
Filter fabric
Concrete or other structural planter wall with waterproof membrane
Additional waterproofing on building as needed
Drain to storm drain or discharge; bottom-out or side-out options
Planter Box
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Planter Box
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Integrated Management Practices
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
Advantages Challenges
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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
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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
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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