Annualmeeting:2017 CSDMS meeting-011

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Two-dimensional modeling of variable-width gravel bed morphodynamics

Jacob Morgan, Colorado State University Fort Collins Colorado, United States. jamorgan@rams.colostate.edu
Peter Nelson, Colorado State University Fort Collins Colorado, United States. peter.nelson@colostate.edu

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Rivers in natural settings are frequently characterized by downstream variations in channel width. However, the effect of width variations on bed topography and sorting patterns remains poorly understood, especially under conditions of changing sediment and hydrologic regimes. In this study we use two-dimensional numerical modeling to systematically explore how the amplitude and wavelength of sinusoidal width variations affect the shape and location of bars, sorting patterns of surface sediment, and the movement of a sediment pulse. We perform simulations with sediment regimes consisting of constant sediment supply, no sediment supply, and a sediment pulse with no background sediment supply. We also perform steady and unsteady flow simulations to explore the combined effect of hydrograph shape and width variations. Preliminary results indicate that width variations force riffle-pool topography with riffles coincident with wider channel sections and pools at narrow sections. The amplitude of width variations is the dominate factor controlling riffle-pool relief. The wavelength of the width variations controls whether central or side bars develop in the wider channel sections. These numerical simulations are complimented with ongoing physical experiments in a laboratory flume and can potentially be used to guide stream restoration and river management practices under conditions of varying sediment and hydrologic regimes.