Low Impact Development Training

Module 4: Bioretention Design Exercise

Neil Weinstein

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Sponsors

District Department of Transportation

U.S. Department of Transportation Federal Highway Administration

The Low Impact Development Center, Inc.

University of the District of Columbia

Funding for this project was provided through a grant from the Federal Highway Administration, U.S. Department of Transportation

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Contributors

The Low Impact Development Center, Inc.

John Shorb Landscaping, Inc.Logo

Groundwork Anacostia River, D.C.

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Copyright

Unless otherwise noted, Low Impact Development Training, funded by DDOT & DDOE, is licensed under a Creative Commons Attribution-NonCommerical-ShareAlike 3.0 Unported License.

Content provided by cited entities remains the property of those entities and may not be used without their explicit permission.

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Overview

• Group exercise to design bioretention cell(s) to capture and treat stormwater runoff from an office park

• Divide into groups of 2-4

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Expected Outcomes

• Design a bioretention cell to meet District retention requirements

• Design a planting plan for bioretention cell

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Materials

• DC Guidebook• Printouts of site – with scale• Calculator• Rulers

Site Plan

Ignore existing storm drains

Plan Courtesy of The Low Impact Development Center, Inc.

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Redevelopment

• Design bioretention cells to intercept retention volume from parking lot

Plan Courtesy of The Low Impact Development Center, Inc.

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Design

• Delineate drainage area• Calculate required retention volume• Find most suitable location(s) • Select most appropriate bioretention

design variation• Calculate size of bioretention required

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Retention requirements

• Retain a volume equal to post-development rainfall from 90th percentile event (1.2 inches)

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Step 1

• Estimate the area of the parking lot using the geometric method

LIDC

Plan Courtesy of The Low Impact Development Center, Inc.

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Step 2

• Calculate the volume of stormwater that needs to be retained (SWRv)

Where • P = target rainfall depth (1.2 inches)• SA = parking lot area (square feet)

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Step 3

• Select a bioretention profile

Ponding depth

Media depth

Gravel depth

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Step 4. Calculate Bioretention Surface Area

• Media porosity = 0.25• Gravel porosity = 0.4

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Step 5. Map out Flowpaths

Plan Courtesy of The Low Impact Development Center, Inc.

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Step 6.

• Determine where to place bioretention• Considerations:

– Intercept stormwater flows (water doesn’t flow uphill!)

– Minimize loss of parking capacity

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Step 7. Planting Plan

• Use plant lists from bioretention specification in the Guidebook

• Create a planting plan using spacing guidelines in the specification

• Take sunlight and optimal location within the bioretention cell into consideration

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Group Presentations