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Lake County Stormwater Management Commission  

Filtering Practices

Filter Strips

Filter strips are typically bands of permanent vegetation, planted between pollutant source areas (such as farmland, cropland, developed land, or other disturbed land) and an environmentally sensitive downstream receiving water body.  A filter strip is an area with dense, preferably native, vegetative cover used to filter and absorb run off from impervious areas. In the context of low impact development, a filter strip should be viewed as only one component in a stormwater management system.


  • Provides infiltration and groundwater recharge.  
  • Removes suspended solids, heavy metals, trash, oil and grease.
  • Reduces peak discharge rate and total volume.

Level Spreader

A level spreader is typically an outlet designed to convert concentrated or channeled runoff to sheetflow and disperse it uniformly across a slope to prevent erosion or to discharge it to treatment devices such as filter strips or bioretention areas. The level spreader is most effective for energy-reduction, which results in increased water infiltration and reduced erosion, but is not effective as a soil sediment removal practice. 

Contour Strips

Contour strips are a series of grass strips that are placed along the slope of the contour in hilly farmland. This helps slow runoff from flowing so quickly down hill resulting in less erosion and therefore a reduced amount of sediment and associated pollutants entering runoff. Contour strips improve water quality while reducing runoff volumes and rates by allowing runoff to infiltrate over a large area. 


  • Reduces runoff rate.
  • Provides infiltration and groundwater recharge.


Photo Credits

  • Filterstrip: Adams County Soil and Water Conservation District
  • Level spreader: North Carolina State University, Stormwater Engineering Group 
  • Contour strip: David Frazer/Corbis

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Waukegan, IL 60085
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