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WED Scientists Participate in Development and Availability of Streamflow Duration Assessment Method for Oregon and Region 10

The Streamflow Duration Assessment Method for Oregon is a scientific tool developed by EPA and the U.S. Army Corps of Engineers to provide a rapid assessment framework to distinguish among ephemeral (flow in direct response to precipitation), intermittent (weekly to seasonal flow), and perennial (year-round flow) streams. Such information helps determine whether a stream may be subject to regulatory jurisdiction under Section 404 of the Clean Water Act and Oregon’s Removal-Fill Law.

The interim method was released on March 6, 2009, for a trial implementation period and has been field tested by interagency teams of State and Federal scientists. It was also the subject of a 2-year validation study, in cooperation with the NHEERL Western Ecology Division (WED), that tested the method at more than 170 sites in western and eastern Oregon during both wet and dry seasons. As a result of that study, the initial 21 field indicators used in the interim version were reduced to just 7 reliable indicators in the final version.

Use of the method is recommended whenever there is uncertainty regarding streamflow duration but is not required. The method provides a scientifically supported, rapid assessment framework to support best professional judgment in a consistent, robust, repeatable, and defensible way. Use of the method may result in more timely and predictable jurisdictional determinations. The method also may provide an initial framework to inform other stream-related issues, such as stream function and compensatory mitigation, and to incorporate relevant tools and procedures as they develop.

ORD continues to collaborate with Region 10 in conducting a validation study of the Streamflow Duration Assessment Method in Washington and Idaho (supported, in part, by Region 10 Regional Applied Research Effort Program funding). Region 10 anticipates releasing a method for use in those States in 2012. The Region 10 lead on the method also has begun a 6-month detail at WED through the Regional Research Partnership Program to continue work on the approach.

Further information is available at http://yosemite.epa.gov/R10/ecocomm.nsf/wetlands/sdam

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