National Water-Quality Assessment (NAWQA) Project

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Effects of Urbanization on Stream Ecosystems

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Photos of Seattle, WA

Maps and pictures of the Seattle study area

Seattle, Washington

Time of study:

Site selection in 2006.
Data collection from fall 2006 to fall 2007.

General Description:

The Seattle study area is located in western Washington, USA. Approximately 3.9 million people lived in the Puget Sound region in 2000. This number represents an increase of 20 percent from the population of 1990. Most of the people live within 20 miles (32 kilometers) of the Puget Sound shoreline in a north-south trending, urban corridor that includes the major cities of Seattle, Tacoma, Bellevue, and Everett.

The study area is in the Puget Lowland ecoregion (Omernik 1987), where open hills and table lands of glacial and lacustrine deposits dominate the landscape. Elevation in the Lowland ranges from sea level to about 2,500 feet (760 meters) above sea level.

The dominant natural vegetative cover is Douglas fir, but forests also include lodgepole pine and western white pine (Black and Silkey, 1998). Riparian zones consist of cottonwood, willow, ash, and alder (Omernik and Gallant, 1986).

The study area has a marine climate characterized by cool, wet winters and warm, dry summers with mean annual temperatures ranging from 50 to 61 degrees Fahrenheit (10 to 16 degrees Celsius) and a mean annual rainfall of 40 inches (102 centimeters). About 80 percent of the annual precipitation falls from October through April with July and August normally the driest months.

Streamflows in the Puget Sound region are typically highest from November through February and lowest in August and September. In the small streams of the Lowland, high flows generally occur in January and February and are dominated by winter rainstorms rather than by snow (Staubitz and others, 1997). Some of the major rivers are regulated; however, the streams of the lowlands typically have few control structures other than stormwater-runoff catchments in the urban areas. Streams in this region support cold-water biological communities including salmon and trout, but are increasingly supporting invasive and warm-water species.

For more information about the study area —

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