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Water Science and Applications

 

Keywords

  • Stream ecology—Congresses
  • Geomorphology—Congresses

Index Terms

  • 1815 Hydrology: Erosion and sedimentation
  • 1824 Hydrology: Geomorphology

Article

WATER SCIENCE AND APPLICATION, VOL. 4, PP. 37-54, 2001

Holocene and recent geomorphic processes, land use, and salmonid habitat in two north Puget Sound river basins

T. J. Beechie, B. D. Collins, and G. R. Pess

The quantity, quality, and distribution of salmonid habitats in the Skagit and Stillaguamish River basins have changed dramatically in response to post-glacial landscape evolution and volcanism over the last 16,000 years, and the more recent history of land use (approximately 150 years). After retreat of the Cordilleran ice sheet about 16,000 years ago, streams incised rapidly into valley-filling glacial sediments, lowering valley floors and creating terraces. Mainstems and floodplain sloughs on valley floors provided the majority of habitat, but moderate-gradient tributaries on terraces provided additional habitat for some salmonids. Channels in bedrock terrain were too steep to support anadromous salmonids and remain so today. Voluminous lahars from Glacier Peak approximately 5,500 years before present created an extensive low-gradient delta on the Skagit River, which then developed abundant habitats in wetlands and distributary channels. Since non-Native American settlers arrived in the mid-1800s, removal of beaver ponds, diking, ditching, and dredging of streams on the floodplains and deltas has isolated or obliterated approximately 50% of the coho salmon winter rearing habitat in both basins. These losses are associated mainly with agricultural practices, which occupy the same landforms as the majority of historical coho salmon habitat. Forestry activities are concentrated on the steeper slopes of the glacial sediments and bedrock terrain, and contribute to habitat losses by increasing sediment supplies and reducing wood abundance. Understanding the interplay of Holocene landscape evolution, geomorphic processes, land use, and salmonid habitat provides a context for developing habitat restoration programs.

Citation: Beechie, T. J., B. D. Collins, and G. R. Pess (2001), Holocene and recent geomorphic processes, land use, and salmonid habitat in two north Puget Sound river basins, in Geomorphic Processes and Riverine Habitat, Water Sci. Appl., vol. 4, edited by J. M. Dorava et al., pp. 37–54, AGU, Washington, D. C., doi:10.1029/WS004p0037.

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