Transcript Watershed Action Plan

Implementing
Low Impact Development
to achieve
water quality benefits
in Contra Costa County
Dan Cloak, P.E.
18 September 2007
Low Impact Development
 Design the
site to mimic
natural
drainage.
 Disperse
runoff to
landscape
where possible.
 Use Integrated Management
Practices distributed around the site.
Swale
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
Contra Costa’s Path to
Low Impact Development
 Stormwater NPDES permit
 Early outreach to
land development community
 Staff work groups developed LID
approach to compliance
 Model ordinance
 Guidebook
 Training for designers & reviewers
 Collaborative problem-solving
LID concept for urban areas
4% of tributary
impervious area
Turf or planting
Planting medium
Gravel or drain rock
Perforated pipe
LID Design
9-acre, mixed use
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Multi-family
Residential
Clay soils
Flat grades
Max. use
Storm drains
Setbacks
Retail
Retail
nursery
Restaurant
Swale “C-2”
 6' to 10' width
fits into
setback
 Underdrain/
overflow to
storm drain
below
Area “C-2”
 Follow roof
peaks and
grade breaks
 Area size
determined by
site layout
 Use valley
gutters instead
of catch basins
25,825 x 0.04 = 1,033 square feet
1,033 ÷ 8 = 129 feet of swale
15 areas; 15 swales
Residential Development
Large hillside project
Difficulties Implementing LID
Developers plan buildings,
streets, parking, and drainage
before considering treatment
requirements
Proprietary devices = quick fix
Integration with landscaping
Deficiencies in construction
What’s worked for Contra Costa
State mandate
Local compliance strategy
● Collaboration and consensus
● Expertise and ownership
Municipal Staff Work Groups
● Mutual support at staff level
● Continuous improvement of
design guidance
Empowering the reviewer
Support from
superiors
Support from
peers
Mandate
Ordinanc
e
Design
Guidanc
e
More info
 Google “Contra Costa Stormwater”
 Other places implementing LID
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San Diego County municipalities
Riverside County municipalities
San Bernardino County
Monterey County
Sacramento County