Quality Indices for Urbanization Effects in Puget Sound Lowland Streams
University of Washington Department of Civil and Environn1ental Engineering QUALITY INDICES FOR URBANIZATION EFFECTS IN PUGET SOUND LOWLAND STREAMS C.W. May, E.B. Welch, R.R. Horner, J.R. Kar and B.W. Mar Final Report for Washington Department of Ecology June 1997 Seattle, Washington 98195 Department of Civil Engineering University of Washington Seattle, Washington 98195 QUALITY INDICES FOR URBANIZATION EFFECTS IN PUGET SOUND LOWLAND STREAMS C.W. May, E.B. Welch, R.R. Horner, J.R. Kar and B.W. Mar Final Report for Washington Department of Ecology Water Resources Series Technical Report No. 154 June 1997 Abstract The Puget Sound lowland (PSL) ecoregion contains an abundance of complex and historically productive salmonid habitat in the form of small streams as well as their riparian forests and wetlands. These watersheds are under intense pressure due primarily to the cumulative effects of urban development. Instream habitat characteristics, riparian conditions, physio-chemical water-quality, and biological attributes of 22 PSL streams (120 survey reaches) were studied over a gradient of development levels to determine relationships between urbanization and stream quality and suggest target conditions for management/protection. Urbanization of PSL watersheds has resulted in an increase in the fraction of total impervious area (% TIA) and a decrease in forested area, including a significant loss of natural riparian forests and wetlands. The cumulative effects of a modified hydrologic (disturbance) regime, the loss ofinstream structural complexity, and the alteration of channel morphological characteristics accompanying urbanization have resulted in substantial degradation of instream habitat during the initial phases of the development process. As the level of basin development increased above 5% total impervious area (% TIA), results indicated a precipitous initial decline in biological integrity as well as the physical habitat conditions (quantity and quality) necessary to support natural biological diversity and complexity.
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