Impervious Cover in the Mianus River Watershed

Many of the implementation projects discussed for the watershed-based plan deal with reducing the negative effects associated with impervious cover. This may mean converting the impervious area to a more porous condition (i.e. gravel to meadow, or a traditional parking lot to porous asphalt), or “managing” the runoff from an impervious area by routing storm flows through a BMP specifically sized to handle that quantity of water.  In less developed parts of the watershed, the strategy is simpler: maintain the low levels of imperviousness through conservation zoning and protection of existing open space.

The watershed-based plan uses The Center for Watershed Protection’s 2003 monograph, Impacts of Impervious Cover on Aquatic Systems, as a basis for its approach. But numerous other sources support the idea of impervious threshholds, including several studies by the CT DEEP summarized in this fact sheet. The Impervious Cover TMDL developed for Eagleville Brook near the University of Connecticut campus offers an excellent case study of the impervious cover approach to managing multiple stressors. Of particular relevance to the Mianus River Watershed is the CT DEEP’s Streams of Hope document, which examines conditions in “moderately urbanized” streams where impervious cover is between 6-14% (impervious cover in the Mianus Watershed is approximately 12%).

We are interested in what measures, if any, your town has taken to deal with the impervious cover issue. Conservation zoning, land protection, and LID can be controversial, and there is no single answer that works for every community. If you would like to offer thoughts or feedback on this topic, you may simply leave a message in the “comments” section of this blog post, or write a new post of your own with one of the generic login IDs. For blog support, contact Lia  (lmastropolo “at” akrf.com).