HR: 0800h
AN: H41D-0771    [Abstracts]
TI: Coupling annual and decadal patterns of sediment flux with channel morphology in gravel- bedded mountain streams
AU: * Grams, P E
EM: grams@cc.usu.edu
AF: Utah State University, Watershed Sciences 5210 Old Main Hill, Logan, UT 84321, United States
AU: Schmidt, J
EM: jschmidt@cc.usu.edu
AF: Utah State University, Watershed Sciences 5210 Old Main Hill, Logan, UT 84321, United States
AU: Majerova, M
EM: milada_majerova@yahoo.com
AF: Utah State University, Watershed Sciences 5210 Old Main Hill, Logan, UT 84321, United States
AB: Channel morphologic parameters that may be expected to change in response to changes in driving variables of streamflow and sediment supply include bed material grain size, bed configuration, channel width and depth, and gradient. Determination of which variable is most likely to respond to a particular perturbation depends on the type and magnitude of perturbation and the time scale of interest. Channel width is often of primary interest because it has the potential to adjust on a decadal time frame and because it is a typical criterion in the evaluation of stream health and function. Changes in channel width associated with changes in flow and sediment flux on large sand-bed rivers have been frequently described. We have initiated a project to evaluate the coupling between changes in flow and sediment flux and channel morphologic variables and on a gravel-bedded mountain stream. On the Cub River in southern Idaho, a series of streamflow diversions have caused changes in the average pattern of runoff. Peak flows are lower in magnitude and of shorter duration in segments affected by greater proportions of floodwater extraction. Field measurements of sediment transport and calibrated transport relations indicate these changes in streamflow have significantly altered the longitudinal sediment flux. Annual sediment flux significantly decreases downstream in years of average to high runoff, in contrast to the stable or increasing flux that our models predict for undiverted conditions. However, have these changes affected channel morphology to a degree that can be detected on a gravel-bedded mountain stream over a period of ~100 years? Detailed longitudinal measurements of bed elevation, channel width, bed material size, bed mobility, and channel configuration indicate that with increasing magnitude of flow extraction (1) channel width and channel width variability decreases, (2) bed elevation variability increases, (3) bed mobility increases, and (4) there is a greater abundance of gravel bars that are in-channel sediment storage sites. We compare these patterns of channel characteristics with the sediment mass balance to determine the relative importance of changes in channel width and in-channel sediment storage in accommodating the estimated longitudinal imbalance of sediment supply and export.
DE: 1824 Geomorphology: general (1625)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1834 Human impacts
SC: Hydrology [H]
MN: 2007 Fall Meeting