Transcript Slide 1
Post Construction Runoff
Control & BMPs
J. C. Hayes, Ph.D., P.E.
& D. Hitchcock, Ph.D.
South Carolina Stormwater Forum
May 8, 2007
Columbia, SC
Post-Construction Water
Quality BMPs
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Post-Construction Water Quality BMPs
• PCWQ BMP Design Criteria
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1. Non-Structural Controls
2. Limited Application Structural Controls
3. General Application Structural Controls
Pre-Fabricated Devices
Selection Process for PCWQ BMPs
Non-Structural Controls
Natural Stream Buffer
Natural Infiltration Area
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Natural Stream Buffer
The general function of stream buffer is to:
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Provide shade for the stream
Provide habitat around the stream
Remove pollutants, bacteria, sediments, and
excess nutrients through infiltration and filtering
Help detain high flow rates from developed areas
Provide a setback to prevent damage to structures
due to flooding or stream channel changes
Natural Stream Buffer
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Natural Infiltration Area
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Undisturbed land area covered with natural
vegetation accepts runoff from new
development and infiltrates runoff into soil.
Natural Infiltration Area
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Limited Application Structural Controls
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Vegetated Filter Strip
Vegetated Channels and Swales
Vegetative Filter Strips
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Rely on vegetation to slow runoff velocities
and filter out sediment and other pollutants
from urban runoff.
To be effective, sheet flow must be maintained
across the entire filter strip.
Once runoff flow concentrates, it short circuits
filter strip and reduces water quality benefits.
A flow spreader is normally part of the design.
Vegetative Filter Strip
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Vegetated Channels and Swales
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Can be designed and installed as alternative
to curb and gutter and hard piping storm water
conveyances.
Improve water quality by providing partial
pollutant removal as water is filtered by
vegetation and by infiltration into soil.
Can also reduce flow velocities when
compared to hard piping systems.
Vegetated Channels and Swales
Maintenance requirements include:
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Periodic inspection for erosion or formation of gullies.
Removal of sediment and debris from channel bottom.
Grass lined swales should be mowed to maintain height
Grass should be mowed once a year.
Vegetated Channels and Swales
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Vegetated Channels and Swales
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General Application Structural Controls
Infiltration Trench
Wet Detention Pond
Sand Filters
Storm Water Wetlands
Bioretention Areas
Dry Detention Pond
Enhanced Grasses Swale
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Infiltration Trench
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Excavated trench filled with stone aggregate
used to capture and infiltrate runoff into
surrounding soils.
Preserves natural water balance by
recharging groundwater.
Removes wide variety of pollutants through
adsorption, precipitation, filtering, and
bacterial and chemical degradation.
Infiltration Trench
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Infiltration - Pervious Materials, Pavers and Concrete
Alternatives to conventional
surface materials
Increases chances for infiltration
Can be used in combinations
Pavers can be expensive
Maintenance…!!!.
Weeds and clogging
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Wet Detention Pond
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Improve storm water quality by detaining runoff
for an extended period of time to allow for
pollutants suspended in the runoff to settle out.
Designed to treat both storm water quantity and
quality.
Among the most cost-effective and widely used
storm water practices.
Can be created by excavating an existing
depression or through embankments.
Wet Detention Pond
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Wet Detention Pond
Benefits include:
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Limitations include:
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Moderate to high removal rates of urban pollutants,
High community acceptance,
Opportunity for wildlife habitat.
Potential for thermal impacts/downstream warming,
Dam height restrictions for high relief areas,
Drainage problems for low relief areas.
Wet Detention Pond
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Sand Filters
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Multi-chamber structure designed to treat storm water
runoff through filtration, using a sediment forebay, a
sand bed as its primary filter media, and an underdrain
collection system.
Typically require 2-6 feet of head.
Should be used on sites that are well-stabilized to
prevent excess sediment from clogging the filters.
Sand Filters
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Sand Filter
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Storm Water Wetlands
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Constructed shallow marsh-like systems
designed to treat both urban storm water and
control runoff volume.
As runoff flows through the facility, pollutant
removal is achieved through settling and
uptake by vegetation.
Storm Water Wetlands
Benefits include:
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Limitations include:
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Good nutrient removal,
Wildlife habitat,
Low maintenance costs.
Large land requirement,
Continuous base flow needed,
Sediment regulation is critical to sustain wetland.
Storm Water Wetlands
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Bioretention Cell (BRC)
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BRCs developed in early 1990’s in Prince
George’s County, MD.
Utilizes planting mixture with both woody and
herbaceous plants to remove pollutants.
Runoff is conveyed as sheet flow to treatment
area, which consists of a grass buffer strip,
ponding area, mulch layer, planting soil mix,
and plants.
Bioretention Cell
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Bioretention Cells
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Dry Detention Pond
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Surface facilities intended to provide temporary
storage of storm water runoff to reduce
downstream water quantity impacts.
Temporarily detains runoff, releasing the flow
over a period of time.
Designed to completely drain following a storm
event and are normally dry between storm
events.
Less costly than wet ponds because less
excavation is required.
Dry Detention Pond
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Enhanced Grassed Swale
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Include filter bed of prepared soil that overlays
underdrain system.
Install berms, check dams, weirs & other
structures perpendicular to flow to promote
settling and infiltration.
Predominantly dry, preferred in residential
settings, or along roads and highways.
Designed to capture water quality runoff
volume, and safely pass larger flows.
Enhanced Grassed Swale
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Pre-Fabricated Control Devices
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Pre-Fabricated stormwater management control
systems may be utilized if adequate pollutant removal
efficiency is demonstrated.
Type of system to be used should be based on ability to
remove pollutants of concern (i.e. bacteria,
hydrocarbons, etc.).
Pollutant removal efficiency data is necessary and
preferably from a third party testing company.
Maintenance is critical on these systems so a detailed
long-term maintenance plan is required.
Pre-Fabricated Control Devices
• Used in urban areas
• Installed with other
stormwater infrastructure
• Usually sized based
on impervious area
• Inspection and
maintenance required
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Pre-Fabricated Control Devices
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Pre-Fabricated Control Devices
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Pre-Fabricated Catch Basin Inserts
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Pre-Fabricated Catch Basin Inserts
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BMPs in Series or
“Treatment Train”
Some BMPs are better than others
for certain pollutants
Consider the connectivity of BMPs
Front-end sediment collection;
i.e., forebays or traps
Vegetated BMPs can be overloaded
so should be toward the end of train
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Design difficulty is that little info is
available to design BMPs to meet
effluent standard
Urban Land
Use
Buffer
Extended
Swale
Pond
(w/ Forebay)
Wetland
Receiving
Waters
Selection Process for Post
Construction Water
Quality BMPs
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References for Additional Info
DHEC OCRM Stormwater BMP Handbook
http://www.scdhec.gov/environment/ocrm/pubs/
docs/SW/BMP_Handbook/BMP_Handbook.pdf
DHEC OCRM BMP Field Manual
http://www.scdhec.gov/environment/ocrm/pubs/
docs/SW/Field_Manual/OCRM_DHEC_FIELD_
MANUAL.pdf
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Questions?