Andrew S. Gendaszek

Effect of river confinement on depth and spatial extent of bed disturbance affecting salmon redds

ABSTRACT Human impacts on rivers threaten the natural function of riverine ecosystems. This paper assesses how channel confinement affects the scour depth and spatial extent of bed disturbance and discusses the implications of these results for salmon-redd disturbance in gravel-bedded rivers. Two-dimensional hydrodynamic models of relatively confined and unconfined reaches of the Cedar River in Washington State, USA, were constructed with surveyed bathymetry and available airborne lidar data then calibrated and verified with field observations of water-surface elevation and streamflow velocity. Simulations showed greater water depths and velocities in the confined reach and greater areas of low-velocity inundation in the unconfined reach at high flows. Data on previously published scour depth of bed disturbance during high flows were compared to simulated bed shear stress to construct a probabilistic logistic-regression model of bed disturbance, which was applied to spatial patterns of simulated bed shear stress to quantify the extent of likely bed disturbance to the burial depth of sockeye and Chinook salmon redds. The disturbance depth was not observed to differ between confined and unconfined reaches; however, results indicated the spatial extent of disturbance to a given depth in the confined reach was roughly twice as large as in the unconfined reach.

Transport and deposition of asbestos-rich sediment in the Sumas River, Whatcom County, Washington

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Hydrogeologic framework and groundwater/surface-water interactions of the South Fork Nooksack River Basin, northwestern Washington

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Geomorphic Framework to assess changes to aquatic habitat due to flow regulation and channel and floodplain alteration, Cedar River, Washington

The Cedar River drains an approximately 460 km watershed within the western Cascade Mountains and the eastern Puget Lowland of Washington State and currently flows into Lake Washington (fig. 1). The upper part of the Cedar River flows into Chester Morse Reservoir, which was impounded behind a late Pleistocene moraine of the Puget Lobe of the Cordilleran Ice Sheet. Similar lakes persisted along the western front of the Cascade Range along neighboring valleys of rivers like Middle Fork and South Fork of the Snoqualmie River; the moraine dams across these valleys were breached much earlier and no lakes persisted through the Holocene to the present day. Human modifications to the hydrology of the Cedar River began in 1901 with the construction of a diversion dam at Landsburg although this dam only functions as a dam to divert water into a municipal water supply pipeline and does not have enough storage capacity to alter the Cedar River’s hydrology. Significant alterations to the magnitude and duration of peak-flow events began with the completion of additional dams to control flow out of Chester Morse Reservoir by 1914. In 1912, a channel was constructed through Renton to divert the Cedar into Lake Washington from its original path into the Black River, an abandoned tributary of the Duwamish River, which ultimately drains into Elliot Bay. By 1916, this diversion supplied water to run locks operated by the U.S. Army Corps of Engineers for ship passage between Lake Washington and Puget Sound. As the floodplain developed during the 20th century, bank protection structures including revetments and levees limited channel migration and confined the Cedar River to a fraction of its former extent. Although sediment is still supplied to the Cedar River from glacial outwash bluffs along the valley margin, sediment input from bank erosion has been severely limited by revetments and levees. Geomorphic Changes