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Date of Award
Master of Science (MS)
Suczek, Christopher A., 1942-2014
Hirsch, David M., 1969-
Pittman, Paul David
Extreme sedimentation in Swift Creek, located in the Cascades foothills in NW Washington (48°55’N, 122°16’W), results from erosion of the oversteepened, unvegetated toe of a large (0.55 km2) active earthflow. The amount of bedload in the creek has necessitated several mitigation projects in the channel including annual dredging and temporary sediment traps in an attempt to reduce the risk of flooding and damage to manmade structures downstream.
The bedload and suspended sediment in the creek are a direct result of the weathering process of the serpentinitic bedrock, in which the landslide is rooted. The serpentinite weathers to asbestiform chrysotile with minor amounts of chlorite, illite and hydrotalcite, all of which occur in clay seeps on the unvegetated surface of the landslide. The chrysotile fibers average 2 μm in length and make up at least 50%, by volume, of the suspended load transported in Swift Creek. The suspended sediment transported by Swift Creek poses a threat to downstream ecosystems in the Sumas River because of the turbidity and heavy metals that Swift Creek introduces into this fish-producing river. This study does not address the environmental or health implications of the asbestiform chrysotile transport or deposition.
During the sampled time between February 2005 and February 2006, the suspended sediment concentrations ranged from 0.02 g/L to 41.6 g/L and the discharge ranged from 0.00 m3/s to 0.51 m3/s.
A nonlinear functional model estimated the total suspended sediment flux from detailed precipitation records and discrete suspended sediment concentration and discharge measurements to be 910 t/km2/yr. That number, coupled with the bedload estimate of 17,600 t/km2/yr, which is based on cross-sectional differences and dredged material, resulted in a total sediment yield of 18,510 t/km2/yr.
The estimated erosion rate for the Swift Creek watershed is 11 mm/yr and 158 mm/yr for the Swift Creek landslide alone. The majority of the material entering Swift Creek is presumed to be originating on the unvegetated toe of the SCL, where the erosion rate is approximately 950 mm/yr.
Western Washington University
Subject – LCSH
Suspended sediments--Washington (State)--Swift Creek (Whatcom County)--Measurement; Bed load--Washington (State)--Swift Creek (Whatcom County)--Measurement; Sediment transport--Washington (State)--Swift Creek (Whatcom County)--Measurement; Erosion--Washington (State)--Swift Creek Watershed (Whatcom County)--Measurement;
Swift Creek (Whatcom County, Wash.); Swift Creek Watershed (Whatcom County, Wash.)
Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this thesis for commercial purposes, or for financial gain, shall not be allowed without the author's written permission.
Bayer, Tovah M. (Tovah Michelle), "The Nature and Transport of the Fine-Grained Component of Swift Creek Landslide, Northwest Washington" (2006). WWU Graduate School Collection. 800.