urban stormwater - dnr · urban stormwater. urbanization urbanization: the development of land,...
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Urban Stormwater
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Urbanization
� Urbanization: the development of land, leading to an increase in the amount of impervious surface in the watershed
� Impervious surface is the sum of all hard surfaces in the watershed� All the surfaces that inhibit infiltration of
rainfall
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Impacts of Urbanization
� Increases in impervious surfaces lead to an increase in water quantity delivered to streams, which results in higher energy
� Land disturbance through development leads to an increase in sediment input and decrease in vegetation
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Impacts of Urbanization
Impervious cover disrupts the natural water balance, dramatically increasing water running off the site
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Typical Stormwater Management
� Curbs and gutters are designed to deliver stormwater away from the road surface in a timely and efficient manner.
� Catch basins or inlets collect stormwater and direct it to a downstream stormwater facility or to receiving waters.
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Typical Stormwater Management
Often, the runoff is directly discharged into nearby waterbodies without water quality treatment.
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Impacts on Hydrology
Large Storm
Small Storm
Higher and More Rapid Peak Discharge
Higher Baseflow
More Runoff Volume
Lower and Less Rapid Peak
Gradual Recession
Dis
char
ge
Time
Pre-Development
Post-Development
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Impacts on Hydrology
An increase in stormwater flow can result in flooding and downcutting of the stream.
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Impacts on Hydrology
Bankfull flooding occurs more frequently in highly urbanized areas and has the potential to
be extremely erosive and damaging to the natural morphology of the stream.
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Impacts on Habitat
In many highly urbanized areas, natural streams have been channelized and lined with concrete to quickly guide runoff, but these streams have lost all habitat value.
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Impacts on Habitat
< 5% impervious surfaces 10% impervious surfaces
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Impacts on Habitat
30% impervious surfaces20% impervious surfaces
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Impacts on Habitat
The surrounding area of this stream is approximately 50% impervious cover. In these
situations streams are often piped.
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Impacts on Habitat
Culverts like these act as barriers to fish migration and cut off spawning areas.
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Impacts on Water Quality
Urbanization causes the temperature of streams to rise, both during low flow and storm
events.
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Impacts on Water Quality
Research shows that at 10% impervious cover, aquatic insect and fish communities in urban streams begin to decline sharply.
� Declines in both the total number of aquatic species and number of sensitive species
� Wetland plants and animals are also adversely impacted by increasing impervious cover.
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Stormwater and Sediment
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Stormwater and Sediment
Sediment can:
� Clog gills
� Bury eggs
� Smother habitats
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Impacts on Stream Channel
Increased sediment input fills in stream channels and decreases invertebrate habitat
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Stormwater BMPs
Aquatic buffers
Agricultural riparian buffers Urban riparian buffers
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Stormwater BMPs
Shared drives & pervious pavers
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Stormwater BMPs
Partial pervious parking surfaces
Primary parking
Overflow Parking
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Stormwater BMPs
Constructed Wetlands
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Stormwater BMPs
Vegetated swales and Bio-retention filtering systems.
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Stormwater BMPs
Rain Gardens
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Stormwater BMPs
Green Roofs
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Watershed Stewardship Programs
Special activities
� Stream Teams
� Storm drain stenciling
� Clean-up days
� Install a rain barrel
� Plant a rain garden
� Grow Native
� Keep lawns 3” minimum
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Economic Benefits � Reduces stormwater
management costs
� Saves mowing and maintenance
� Avoid drainage complaints
� Increases property values and sales
� Attracts wildlife
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Additional ResourcesCenter for Watershed Protection:� www.cwp.orgStormwater Manager’s Resource Center:� www.stormwatercenter.netEnvironmental Protection Agency:� http://www.epa.gov/owow/nps/urbanmm/� http://water.epa.gov/scitech/wastetech/guide/
stormwater/Low Impact Development Center:� www.lowimpactdevelopment.org