NATURAL RESTABILIZATION OF STREAM CHANNELS IN URBAN WATERSHEDS1

Authors

  • Patricia C. Henshaw,

  • Derek B. Booth

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    • 2

      Center for Urban Water Resources Management, University of Washington, Box 352700, Seattle, Washington 98195 (present address for Henshaw: Northwest Hydraulic Consultants, Inc., 16300 Christensen Road, Suite 350, Tukwila, Washington 98188) (E-Mail/Henshaw: phenshaw@nhc-sea.com).


  • 1

    Paper No. 99179 of the Journal of the American Water Resources Association.Discussions are open until August 1, 2001.

Abstract

ABSTRACT: Stream channels are known to change their form as a result of watershed urbanization, but do they restabilize under subsequent conditions of constant urban land use? Streams in seven developed and developing watersheds (drainage areas 5–35 km2) in the Puget Sound lowlands were evaluated for their channel stability and degree of urbanization, using field and historical data. Protocols for determining channel stability by visual assessment, calculated bed mobility at bankfull flows, and resurveyed cross-sections were compared and yielded nearly identical results. We found that channel restabilization generally does occur within one or two decades of constant watershed land use, but it is not universal. When (or if) an individual stream will restabilize depends on specific hydrologic and geomorphic characteristics of the channel and its watershed; observed stability is not well predicted by simply the magnitude of urban development or the rate of ongoing land-use change. The tendency for channel restabilization suggests that management efforts focused primarily on maintaining stability, particularly in a still-urbanizing watershed, may not always be necessary. Yet physical stability alone is not a sufficient condition for a biologically healthy stream, and additional rehabilitation measures will almost certainly be required to restore biological conditions in urban systems.

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