The U.S. Environmental Protection Agency, Region 10 and the U.S. Army Corps of Engineers, Portland District have published the final version of a procedure to determine the duration of flow in Oregon’s streams, the Streamflow Duration Assessment Method for Oregon (Nadeau T.-L., 2011).  Duration of flow is important in determining whether a stream falls under Clean Water Act regulatory jurisdiction of the U.S. EPA and U. S. Army Corps of Engineers under Section 404 (discharging dredge or fill material into waters of the United States).  In Oregon, many projects requiring a Section 404 permit also require an Oregon Department of State Lands permit under Oregon’s Removal-Fill Law.

This method assesses a suite of indicators to determine whether a stream is ephemeral, intermittent or perennial.  Ephemeral streams are fed primarily by stormwater runoff and flow only for a short time in direct response to precipitation.  Intermittent streams flow for a more sustained period of time than ephemeral streams, usually in winter and spring when the stream bed is below the water table, and may also be fed by snowmelt from surrounding uplands.  Perennial streams contain water continuously during a year of normal rainfall, and are fed by groundwater supplemented by snowmelt and stormwater runoff.

Xerces worked with EPA and USACE to review the current literature on using macroinvertebrates as indicators of stream duration, and provided a recommended aquatic invertebrate taxa list, field methodology, scoring protocol, and field guide to inform the macroinvertebrate scoring portion of the interim version (read the full report) released in 2009.  Following extensive field testing, the initial 21 field indicators used in the interim version, which included a suite of macroinvertebrate indicators, were reduced to seven reliable indicators in the final version—three of which relate to aquatic macroinvertebrates.

In 2011 and 2012, Xerces will again work with the EPA Region 10 Office to develop similar aquatic invertebrate indicators, supporting scientific documentation, and a field guide to support streamflow duration assessment methodologies for Idaho and Washington.  It is important to implement a standardized method to accurately determine the duration of streamflow at potential project sites, and Xerces is pleased to have the opportunity to continue to contribute to this important work.

Acknowledgements
The Xerces Society would like to thank the following individuals who contributed their expertise, including:
• Larry Eaton, North Carolina Division of Water Quality, Raleigh NC
• Ken Fritz, U. S. Environmental Protection Agency, Cincinnati OH
• Bill Gerth, Faculty Research Assistant, Oregon State University
• Jim Johnson, Odonatist, Vancouver WA
• Judith Li, Professor Emeritus, Oregon State University, Corvallis OR
• Dennis Paulson, Director Emeritus, Slater Museum of Natural History, Seattle WA
• Perianne Russell, North Carolina Division of Water Quality, Raleigh NC
• Robert Wisseman, Aquatic Biology Associates Inc., Corvallis OR

Additional information

Oregon Streamflow Duration Assessment Method
Interim Oregon Streamflow Duration Assessment Method
Clean Water Act Jurisdiction: Waters of the United States , U. S. Environmental Protection Agency
The Clean Water Act, U. S. Environmental Protection Agency
The Clean Water Act: An Owner’s Manual, 2nd edition, River Network
Field Operations Manual for Assessing the Hydrologic Permanence and Ecological Condition of Headwater Streams, Fritz, K.M., Johnson, B.R., and Walters, D.M., 2006. EPA/600/ R-06/126. U.S. Environmental Protection Agency, Office of Research and Development, Washington DC
Identification methods for the origins of intermittent and perennial streams, Version 3.1. North Carolina Department of Environment and Natural Resources, Division of Water Quality, Raleigh, NC, 2005