Geologic Publications for Mount Rainier
Deciphering the impacts of glacial melt, lahars, debris flows, flood regulation, levees, and downstream channel avulsion on sediment transport in the White River, Mt. Rainier, Washington State
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Joanna C. Curran
Gravel Bed Rivers 9, Villarrica, Chile
A critical first step in managing a gravel and sand river through a populated area is measuring sediment transport rates to identify areas of persistent erosion or aggradation and trends in bed grain size distribution; to understand the relative influence of large and small flows over sediment mobility and bed exchange and long-term channel adjustment to external perturbations. In rivers transporting sediment sizes from silt to boulders, data collection necessarily includes multiple approaches, both direct and indirect. Sediment measurement efforts, and how collected data are used to understand and manage the river, are described for a river in the Cascade Mountains in Washington State.
The White River originates at Emmons Glacier on Mount Rainier and flows approximately 105 km downstream to a confluence with the Puyallup River and then another 16 km to Puget Sound. It is a wandering channel in that it has an irregularly sinuous planform with both meandering and braided reaches. Sediment eroded from Mt Rainier transports by debris flows, lahars, and atmospheric river driven floods. Flow and sediment transport rates are altered by operations at Mud Mountain Dam at RKm 42 and a fish trap and barrier at RKm 34. Bed surface and subsurface sediment samples have repeated throughout the river but transport data are less frequent. Suspended sediment was measured in the 1970s. Direct bedload sampling was undertaken in 1974 with a Helley Smith at RKm 34 and again in 2010 with an Elwha Sampler at RKm 14. Recent analyses have focused on indirect estimates of transport though bed volume change. Repeat LiDAR, aerial imagery, and Structure-from-Motion have been applied to develop hypotheses of ongoing channel bed adjustment to a 1906 avulsion that lowered the channel between RKm 118. A recent levee setback at RKm 8 is being monitored for its impact on bed elevations and side channel deposition rates. Current efforts are focused on the reach at the barrier where sediment transport occurs only when river flow exceeds 113 m3/s and the barrier gates are lowered. Reach bathymetry is measured after each transport event and sequential data sets differenced to estimate the minimum sediment transport volume past RKm 34 with each high flow and over each water year. Hydrophones have been installed 300 meters downstream of the barrier to monitor gravel transport. The hydrophone signal will be correlated to the measured bathymetric change over the barrier reach.
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In Text Citation:
Curran (2023) or (Curran, 2023)
Curran, J.C., 2023, Deciphering the impacts of glacial melt, lahars, debris flows, flood regulation, levees, and downstream channel avulsion on sediment transport in the White River, Mt. Rainier, Washington State: Poster, Gravel Bed Rivers 9, Villarrica, Chile,