HR: 11:05h
AN: H42B-04 INVITED     [Abstracts]
TI: Response of River Bars to Discharge Variations
AU: * Nelson, J M
EM: jmn@usgs.gov
AF: US Geological Survey, Box 25046, MS 413, Lakewood, CO 80225 United States
AU: Kinzel, P J
EM: pjkinzel@usgs.gov
AF: US Geological Survey, Box 25046, MS 413, Lakewood, CO 80225 United States
AU: McDonald, R R
EM: rmcd@usgs.gov
AF: US Geological Survey, Box 25046, MS 413, Lakewood, CO 80225 United States
AB: Designing controlled hydrographs that produce desirable morphologic characteristics in rivers requires a detailed understanding of the linkage between flow, sediment tranport, and local erosion and deposition. For example, developing flow scenarios in managed rivers that optimize river bar forms (e.g., point bars, alternate bars, braid bars, and lateral separation bars) for habitat enhancement or other objectives requires the ability to predict how various bars respond morphologically to a given discharge or a time series of discharge. Using a variety of field and laboratory measurements in conjunction with computational models for predicting flow and bed evolution, we investigated the response of bar forms in natural rivers to discharge variations. In particular, our investigation concentrated on the effect of hydrograph stage and discharge on bar growth rate and amplitude, and on the important role of hydrograph ramping rates on bar morphology, especially during waning flow. Our results show that using similar quantities of water can produce drastically different morphologic results depending on the duration and amplitude of flow releases. Similarly, different post-flood ramping rates can result in much different quantities and spatial distributions of sub-aerial bar extent at lower flows. Taken together, our results indicate that predictive methods are useful for designing hydrographs to achieve management objectives regarding bar morphology. Furthermore, through comparison of measurement and computation, we confirm that even a relatively simple coupled model for flow and sediment transport provides good predictions of bar response to hypothetical hydrographs, and can be used to help design such flow scenarios.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting