See more from this Division: General Discipline Sessions
See more from this Session: Environmental Geoscience I - Natural Hazard Assessment, 3D Modeling, and Site Characterization
Abstract:
Mud deposits upstream of the reservoir occur as bars and thin layers in slow-moving parts of the channel. Grain sizes are clay to very fine sand, similar to those in the reservoir. Abundant, horizontally oriented plant fragments and clastic sediment form crude layers. Roots are abundant. Features indicate that the clastic sediment was deposited in slow moving or stagnant water, with vegetative layers reflecting yearly accumulations of plant detritus.
The river gravel is supplied by erosion and winnowing of fines from glacial and periglacial bank sediment. Flow modeling indicates that grain sizes up to coarse sand could be carried in suspension during bankfull flow. The distribution of mud deposits downstream of the reservoir as bars, fills of anabranches, and thin layers on the surfaces of gravel bars is inconsistent with typical fluvial processes of mud deposition. The mud deposits range from clay to very coarse sand, with a high proportion of coarse grains. Deposits are homogeneous and lack primary sedimentary structures. Surface vegetation is absent. Evidence indicates that the mud resulted from the catastrophic release of sediment and water from the reservoir, producing a hyperconcentrated flow that resuspended and mixed with coarser river sediment before rapid deceleration and deposition.
See more from this Division: General Discipline Sessions
See more from this Session: Environmental Geoscience I - Natural Hazard Assessment, 3D Modeling, and Site Characterization