Evaluating Stormwater BMPs

Frank HenningRegion IV Land Grant Universities Liaison

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Insert Unit # and Title

What Low Impact DevelopmentIs and Is Not

LID Is: LID Is Not:

Volume control for small storms Major flood control

Better stormwater management for new & existing development

Anti-development

Requires complementary approaches for large storms

A stand-alone solution for all wet weather management

Scale site specific solution One size fits all

Mimics natural hydrology Dry up all the streams

Cost competitive to traditional stormwater management

Free

Georgia Stormwater Management Manual, Vol. 2ARC 2001

StormpondDesignVolumes

Water Quality

Volume

Knoxville, TN Development Manual

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Reducing Runoff Volume

Flow Volume

Green Infrastructure/LID

– Preserves natural environments– Retains stormwater volume for infiltration,

evapotranspiration, or use– Removes the volume from the stream– Mimics natural hydrology, often enhances groundwater

recharge and base flow – Removes pollutant load associated with the volume

retained– Does not transfer pollution to ground water– May need additional storage to address stream

protection and flood prevention requirements

Natural Area Preservation

Storage volume = predevelopment conditions Natural areas generally are counted as net zero Can they store, infiltrate, evapotranspirate more than the design volume?

Soils and vegetation – already present = free Inlet/Outlet control – direct inflow/overland flow = free

Wetlands Franklin, TN Maryville TN Buffers Maryville TN Springhead

Soil Enhancement Program• Cost – usually minimal or low• Storage – enhance void space and infiltration

rate of soil • Soil – amended soil and native soil infiltration

rate• Vegetation – selection based on site• Inlet/Outlet – direct inflow, overland or directed

Vegetative Cover

- Proper fertilizer and pesticide use - Maintain vegetative cover - BMP is a nutrient sink, not a nutrient source (how green is green?)- Stormwater contains nutrients

Reduce Pollutant Loads

Disconnection Programs

• Storage – based voids, and infiltration rate of soil, impervious area disconnected (capture area)

• Soils – amended or uncompacted native soil• Vegetation – selection based on the site• Inlet/Outlet – downspouts, sheet flow over vegetated

areas to swales, sewers, waterbodies

Tree Canopy Programs

• Storage volume - based on pool volume, void space of amended soil, native soil infiltration rate, evapotranspiration rate, capture area

• Soil – structural or amended for storage/pollutant uptake

• Vegetation - trees for largest amount of evapotranspiration, other benefits

• Inlet /Outlet Controls – must provide!

Rainwater Harvesting & Use• Storage volume – • Water Use – irrigation or other use • Soils - infiltration• Vegetation – evapotranspiration• Inlet/Outlet - must be provided• Outlet protection – reduce erosion

Green Parking – Permeable Pavement

Green Roofs

• Storage – soil depth/voids• Soils – amended, structured• Vegetation – intensive (shallow soil-

sedums or drought tolerant species)or extensive (deep soil-small tree, shrubs)

• Inlet /Outlet – direct capture/roof drains• Structural – must perform analysis

Raingardens/Bioretention

• Storage Volume – based on pool design, amended soil void space, capture area

• Soils - native soils are removed and replaced with amended soil

• Vegetation - herbaceous (low evapotranspiration)• Inlet/ Outlet controls - direct inflow and

provide for bypassing larger events

Volume Comparison

Burnsville, MNNeighborhoodRain GardenStudyBarr Engineering

Other GI/LID Benefits

• Air quality improvement• Community beautification• Energy savings• Health benefits• Heat island reduction• Property value improvement• Recreation and wildlife

AcknowledgementsModule contributors:

Material for this module was adapted from presentations and publications byRegion IV EPA Watershed Protection Division

Module editors:[Insert names and affiliations here for at least 2 peer-reviewers]

Southern Region Landscape Team:Amy Shober (UF/IFAS); Lucy Bradley (NCSU); Eve Brantley (Auburn); Wendi Hartup (NCSU); Barbara Fair (NCSU); Frank Henning (USEPA/UGA); Esen Momol (UF/IFAS); Kerry Smith (Auburn); Dotty Woodson (Texas Agrilife); Sheryl Wells (UGA)

Funding for this module provided by: USDA-NIFA National Water Program, Southern Regional Water Program special project funds

Graphic design:Emily Eubanks - UF/IFAS Center for Landscape Conservation and Ecology; Amy L. Shober – UF/IFAS Gulf Coast Research and Education Center

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