January 11, 2012

FAQ: When does a community have to apply Low Impact Development techniques?

The Reasonable and Prudent Alternative (RPA) requires communities to incorporate Low Impact Development (LID) techniques as an element of their storm water management in the Special Flood Hazard Area (SFHA).  

LID techniques that primarily focus on infiltration may not be feasible in the floodplain due to factors such as high groundwater levels that are typically found in floodplain environments. Soil quality, slope, and drainage are additional factors that may limit the feasibility of using LID techniques.  
In some floodplains LID techniques that are focused on water quality (rainwater collection and reuse, vegetation retention, and bioswales) are more likely to be successful than infiltration for meeting habitat goals.  
LID is a storm water management strategy that emphasizes conservation and the use of existing natural site features integrated with distributed, small-scale storm water controls to mimic natural hydrologic patterns.  LID is more than on-site infiltration of storm water (e.g., through rain gardens and pervious surfaces) - LID also captures and stores water for later reuse, filters out pollutants, and slows down water velocities.  
 LID works best when used throughout a community or watershed, not just in the floodplain.  While LID is a preferred method for storm water management in the Biological Opinion, communities may be able to demonstrate that their storm water management program achieves similar goals to LID in areas where LID may not be feasible.  The Ecology Stormwater Manual and the NPDES permits require communities to mimic pre-development flows through more traditional techniques while encouraging the use of LID techniques.  Where infiltration is not feasible, techniques that contribute to water quality should still be considered.

For more information regarding the use of Low Impact Development please visit these sites:

http://www.lowimpactdevelopment.org/publications.htm

http://www.psp.wa.gov/downloads/LID/LID_manual2005.pdf






	


U.S. Department of Homeland Security
Region X
 130 228th Street SW
 Bothell, WA 98021-9796





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