Monday, May 26, 2008 - 10:15 AM
26

Urbanization eliminates ephemeral and intermittent stream length and increases perennial flow

Allison H. Roy, US Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, 26 West Martin Luther King Drive, Cincinnati, OH 45268, Angel L. Dybas, Cornell Cooperative Extension of Suffock County, Vanderbilt Museum, 180 Little Neck Road, Centerport, NY 11721, Ken M. Fritz, U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Division, 26 West Martin Luther King Dr., Cincinnati, OH 45268, and Hannah R. Lubbers, Department of Biological Sciences, University of Cincinnati, PO Box 210006, Cincinnati, OH 45221-0006.

Protection of headwater streams under the Clean Water Act has been under scrutiny in recent Supreme Court cases, leading to renewed interest in the extent of non-perennial tributaries and their connections to downstream navigable waters.  In this study, we assessed the effects of urbanization on the location and length of ephemeral, intermittent, and perennial streams.  We randomly selected 150 of 6,686 stream origins in Hamilton County (Cincinnati), Ohio, which has 50% urban, 36% forest, and 11% agriculture land cover.  Of the points visited, 63% had no stream channel, primarily because streams were piped.  In forested landscapes, mean catchment areas for stream channel origins were smaller than origins in developed areas, reflecting the loss of stream channels in urban areas.  Urban development resulted in a 93% and 46% loss of ephemeral and intermittent channel length, respectively, and a 22% gain in perennial channel length county-wide.  Catchment relief explained 60–74% of the variation in catchment area of stream origins.  Decreased perennial area was further explained by reduced forest cover and increased septic density.  Urbanization may decrease (e.g., by reducing infiltration) and increase (e.g., by reducing evapotranspiration) the permanence of flows, thus confounding the effect of land cover on hydrologic permanence.    


Web Page: urban, hydrology, headwater

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