Low Impact Development

[presenters name][presentation date]

Integrated Management Practices

Controlling Stormwater Quality and Quantity using

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 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.

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

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

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

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

Planter Box

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

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