My last posting about the return of the American eel to Donaldson Run and Gulf Branch ended with the phrase “let’s try to keep it that way.” One reader asked me the logical follow-up question: how? How do we make sure that Arlington continues to provide habitat for these catadromous fish?
The easy answer is to prevent the type of pollution event that occurred during the summer of 2001 when the runoff from an herbicide application by the Washington Golf and Country Club killed hundreds of American eels in Donaldson Run and Gulf Branch. The harder answer is somewhat counter-intuitive: too much water in our streams can damage their habitat too.
Storm water runoff can destroy our streams by creating what is known as the “urban stream syndrome.” As urbanization increases, a stream’s watershed becomes increasing filled with more and more impervious surfaces, that is, the hard surfaces that prevent rainwater from seeping gently into the soil. Instead, rainwater flows off these impervious surfaces directly into the nearest stream. Significant storms can turn small streams into raging torrents of water.
With the force of a fire hose, these streams scour their banks into deep “V-shaped”ravines and flush sediment, organic matter, and insect life downstream. All bad news for the American eel!
According to Arlington’s Watershed Management Plan, “stream degradation begins when imperviousness exceeds 10 percent, and significant deterioration occurs beyond 25 percent imperviousness.” The Watershed Management Plan calculates that the watersheds for both Donaldson Run (11%) and Gulf Branch (14%) are in danger of this type of stream degradation.
Preventive measures include voluntary conservation easements over the private lands in both watersheds (“green infrastructure”) and retro-fitting existing impervious surfaces with pervious concrete (“gray infrastructure”). Other helpful tools include the use of rain barrels and rain gardens. In addition, completely re-building the degraded stream banks---such as was done for that portion of Donaldson Run near Military Road --- will help stop the “urban stream syndrome.”
Hopefully, both private and public landowners in the watershed will use these and other measures to preserve the habitat of the American eel in Arlington. It would be a shame if continued urbanization made our streams inhospitable for these intrepid visitors to our fair county.
Mike Nardolilli serves as President of the Northern Virginia Conservation Trust, President of the Arlington Outdoor Lab, and as a Member of the Board of Directors of the Northern Virginia Regional Park Authority.
