HR: 0800h
AN: H51I-0903    [Abstracts]
TI: Modified Sediment Rating Curve Approach for Supply-dependent Conditions
AU: * Wright, S A
EM: sawright@usgs.gov
AF: U.S. Geological Survey, 6000 J Street, Sacramento, CA 95819,
AU: Topping, D J
EM: dtopping@usgs.gov
AF: U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001,
AU: Rubin, D M
EM: drubin@usgs.gov
AF: U.S. Geological Survey, 400 Natural Bridges Drive, Santa Cruz, CA 95060,
AU: Melis, T S
EM: tmelis@usgs.gov
AF: U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001,
AB: Reliable predictions of sediment transport and river morphology in response to driving forces, such as anthropogenic influences, are necessary for river engineering and management. Because engineering and management questions span a wide range of space and time scales, a broad spectrum of modeling approaches has been developed, ranging from sediment transport rating curves to complex three-dimensional, multiple grain-size morphodynamic models. Sediment transport rating curves assume a singular relation between sediment concentration and flow. This approach is attractive for evaluating long-term sediment budgets resulting from changes in flow regimes because it is simple to implement, computationally efficient, and the empirical parameters can be estimated from quantities that are commonly measured in the field (sediment concentration and flow). However, the assumption of a singular relation between sediment concentration and flow contains the following implicit assumptions: 1) that sediment transport is in equilibrium with sediment supply such that the grain-size distribution of the bed sediment is not changing, and 2) that the relation between flow and bed shear stress is constant. These assumptions present limitations that have led to the development of more complex numerical models of flow and morphodynamics. These models rely on momentum and mass conservation for water and sediment and thus have general applicability; however, this comes at a cost in terms of computations as well as the amount of data required for model set-up and testing. We present a hybrid approach that combines aspects of the standard sediment rating curve method and the more complex morphodynamic models. Our approach employs the idea of a shifting rating curve, whereby the relation between sediment concentration and flow changes as a function of the sediment budget in the reach. We have applied this alternative approach to the Colorado River below Glen Canyon Dam. This reach is particularly suited to such an approach because it is substantially sediment supply-limited such that transport rates are dependent on both flow and sediment supply; also, there is a rich dataset available for constraining the empirical parameters and testing the hybrid model. Though more empirical in nature than the morphodynamic models, this modified sediment rating curve approach may have broad potential application because its simplicity allows for relatively rapid evaluation of long-term sediment budgets under a range of flow regimes and sediment supply conditions.
DE: 1808 Dams
DE: 1815 Erosion
DE: 1847 Modeling
DE: 1861 Sedimentation (4863)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting