ON-DEMAND CONTINUOUS MASS-BALANCE SEDIMENT BUDGETS FOR RIVER SCIENCE AND MANAGEMENT (Invited Presentation)

Recent advances in techniques for making sediment-transport measurements have allowed for the on-demand construction of continuous mass-balance sediment budgets, available at https://www.gcmrc.gov/discharge_qw_sediment/. These budgets are constructed using 15-minute acoustical suspended-sediment measurements (calibrated and verified by conventional suspended-sediment samples) and estimates of sand bedload calculated on the basis of dune-migration measurements. Uncertainty in these budgets is computed on the basis of the maximum likely persistent bias in measurements of water discharge, suspended-sediment concentration, and bedload. Because of the possible presence of these biases, uncertainty in flux-based sediment budgets increases over time. These flux-based mass-balance sediment budgets have been found to agree, within overlapping uncertainty, with topographic-based sediment budgets in two independent comparisons conducted in 42- and 50-km-long river segments in which the vast majority of these long river segments were repeat-mapped using multi-beam sonar. Continuous mass-balance sediment budgets are being used to inform scientists and managers in the Yampa, Green, and Colorado rivers and Rio Grande. In the case of the Colorado River in Grand Canyon National Park, these budgets are used to design and evaluate water releases at Glen Canyon Dam. In the cases of the Yampa and Green rivers in Dinosaur National Monument and the Ouray National Wildlife Refuge, and the Rio Grande in Big Bend National Park, these budgets are used to determine the combination of flow and sediment supply required to maintain sufficient channel complexity for aquatic habitat. Although continuous sediment budgets constructed using sediment-transport measurements do not allow determination of the specific locations in a river segment where topographic change is occurring (in contrast to topographic-based sediment budgets), they do provide a near-realtime measure of gross change in river-channel geometry, with calculable error that is less than the extrapolation error in under-sampled topographic-based sediment budgets.