Shoreline Management photo

Shoreline Management

USGS reports on streams meeting SMA jurisdiction criteria

The Shoreline Management Act (SMA) applies to rivers from the mouth upstream to a point where the "mean annual flow" is 20 cubic feet per second (20 cfs). The current rule defining streams and rivers under SMA jurisdiction is found in WAC 173–18.

The stream points in that rule were developed from a systematic streamflow study prepared by the United States Geological Survey (USGS) in 1971.

In the 1990s Ecology commissioned USGS to prepare a series of reports to determine more accurate shoreline boundaries. Because direct measurement of flow for all streams is impractical, USGS researchers used computerized models based on watershed area and rainfall/runoff relations, fine-tuned with stream gage records gathered over decades.

The current reports are more accurate than the original survey because they benefit from two more decades of rainfall and streamflow data. The studies indicate some stream reaches on the current adopted list do not meet jurisdiction criteria, however, overall they indicate many more additional miles that flow at 20 cfs. Most of the additional stream miles are at high elevations on federal forest lands that were not classified in the 1971 study.

While some of the differences are the result of a more complete assessment, some points changed because water has been diverted, or because land use patterns have altered a basin’s runoff characteristics.

The following reports describe the USGS study methodology and findings.

For more information

For more information contact Tim Gates at or 360-407-6522.