New Oregon streamflow assessment tool aids Clean Water Act compliance

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PORTLAND, OR, Dec. 1, 2011 -- The challenging task of determining if a particular stream is protected under federal and state fill and disposal regulations just became a little easier. The new Streamflow Duration Assessment Method for Oregon will help natural resource professionals, consultants and regulators identify whether a fill or removal project with potential stream impacts must obtain permits.

Section 404 of the federal Clean Water Act and Oregon's Removal-Fill Law require permits to protect water resources when someone plans to place soil, dredged or other material in regulated waters.

This new method provides a consistent, repeatable and quick way to identify whether an Oregon stream is intermittent, perennial or ephemeral. Intermittent streams, which flow seasonally, and perennial streams, which flow continuously, are typically subject to both state and federal regulations. Ephemeral streams only flow after rainfall or during snowmelt, and under current agency practice are protected under the Clean Water Act if they have a significant effect on the integrity of larger downstream waters.

The science-based tool was released in November after a two-year trial run. The method was tested and refined at over 170 sites in western and eastern Oregon during both the wet and dry seasons. During the field trial, the initial 21 indicators were reduced to just 7 reliable indicators.

The method proved accurate in many environments including natural, modified and braided channels. It is a scientific tool that is useful anytime the duration of streamflow must be determined, and may help identify other stream-related issues. Because of the demonstrated benefit in Oregon, the method is already being adapted for use in Idaho and Washington.

"We think this tool will help people understand when to get a permit and help the permitting process move faster and more smoothly," said EPA's Dr. Tracie Nadeau, Environmental Scientist. "Many people collaborated to develop and refine this assessment method, which uses solid science to help protect the waters of Oregon and the United States."

The Streamflow Duration Assessment Method for Oregon was developed by scientists and technical experts from the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers and the Oregon Department of State Lands. The method is recommended for use whenever there is uncertainty about streamflow duration.

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