HR: 17:10h
AN: H34A-05    [Abstracts]
TI: Controlled Floods, Geomorphic Processes, and Riparian Vegetation Mortality in a Sand-Bed Desert River
AU: * Wilcox, A C
EM: andrew.wilcox@umontana.edu
AF: University of Montana, Department of Geosciences, Missoula, MT 59812,
AU: Shafroth, P B
EM: shafrothp@usgs.gov
AF: U.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO 80526,
AU: McDonald, R R
EM: rmcd@usgs.gov
AF: U.S. Geological Survey, Geomorphology and Sediment Transport Laboratory, Golden, CO 80403,
AB: We investigate interactions among flow, geomorphic processes, and riparian vegetation using field studies and computational modeling in an effort to improve both process understanding and the quantitative basis of ecosystem flow prescriptions. We examined the response of native and non-native riparian seedlings and channel morphology to prescribed dam-released floods to maintain a Populus-Salix riparian woodland system on the Bill Williams River, Arizona, USA. Floods in consecutive years produced substantial density reductions among cohorts of one-year old seedlings in two study reaches, with greater reductions among non- native Tamarix seedlings than native Salix seedlings. Little or no mortality occurred among more mature vegetation, however, in part because of the greater drag produced by larger plants. Mechanisms of seedling mortality differed as a function of reach-scale channel morphology and potentially basin-scale sediment supply, with scour-related mortality occurring in a sediment-starved reach and aggradation and burial-induced mortality occurring in a downstream reach with greater sediment supply. We also assessed spatially distributed velocity, shear stress, and sediment mobility associated with floods on the Bill Williams River using the US Geological Survey Multidimensional Surface Water Modeling System and compared the modeled hydraulics to observed seedling responses. Our results illustrate that in sand-bed rivers, even relatively small floods generate sufficient hydraulic forces and geomorphic changes to substantially influence seedling establishment and mortality. Further, controlled flood releases to reduce Tamarix density before seedlings become established (i.e., in their 1st year) may be a method of managing streamflow to provide natives with a competitive advantage over Tamarix. Combining field studies with multi-dimensional hydraulic modeling provides a means of quantifying the potential geomorphic and ecological effects of high flows and therefore can assist development of flow prescriptions to achieve restoration goals.
DE: 1808 Dams
DE: 1813 Eco-hydrology
DE: 1821 Floods
DE: 1825 Geomorphology: fluvial (1625)
SC: Hydrology [H]
MN: 2007 Fall Meeting