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Development and field verification of an indicator-based method for evaluating the duration of streamflow in Oregon
Citation:
NADEAU, T. AND P. J. WIGINGTON JR. Development and field verification of an indicator-based method for evaluating the duration of streamflow in Oregon. Presented at 2009 Annual Water Resources Conference, Seattle, WA, November 09 - 12, 2009.
Impact/Purpose:
In light of the U.S. Supreme Court’s Rapanos decision and Justice Scalia’s focus on “relatively permanent” tributaries, the U.S. Army Corps of Engineers (Corps) and U.S. Environmental Protection Agency (EPA) now place greater emphasis on determining the duration of stream flow in making Clean Water Act Section 404 jurisdictional determinations.
Description:
In light of the U.S. Supreme Court’s Rapanos decision and Justice Scalia’s focus on “relatively permanent” tributaries, the U.S. Army Corps of Engineers (Corps) and U.S. Environmental Protection Agency (EPA) now place greater emphasis on determining the duration of stream flow in making Clean Water Act Section 404 jurisdictional determinations. Because there are many non-perennial streams in Oregon for which there are no reliable flow records, the Corps Portland District and EPA Region 10 Oregon Operations Office cooperatively developed a field assessment method that can be used to distinguish between perennial, intermittent and ephemeral streams in Oregon. The method, released as an interim version on March 6, 2009, uses a suite of readily observed geomorphic, hydrologic, and biologic indicators representing a stream process or feature. Each indicator is assigned a numeric score using a weighted scale, and the flow duration is predicted based on the cumulative score for a given stream reach. The method also provides a common technical framework to address other stream-related issues such as compensatory mitigation and function. To verify the method, EPA is conducting a study applying the method to 177 stream reaches in multiple hydrologic landscape regions across the state, during both wet and dry seasons, and comparing predicted and observed flow durations. We have completed data collection for both a dry and wet season sampling. We anticipate further verification to facilitate the transfer of this method for use across the Pacific Northwest.