University of Montana, Maureen and Mike Mansfield Library
Abstract
Understanding and predicting flood-induced geomorphic change, and the relative influences of fluvial forces and valley-bottom geometry on system response, are persistent quandaries in geomorphic process studies. We combine field surveys, remote sensing, and hydraulic modeling to assess the hydrogeomorphic effects of historic flooding in northern Yellowstone National Park (YNP) in a variety of channel configurations. We compare impulse, a metric that incorporates a flow duration threshold based on threshold channel theory, grain size, channel-bed slope, and flood depth and stream power estimates with hydrogeomorphic response. Measurements of pre- and post-flood active-channel width change in aerial photos captured geomorphic response associated with deposition-related channel migration while a transect-based metric of bed elevation change from pre- and post-flood DEMs of difference captured erosion-related channel evolution. Hydrogeomorphic response to flooding correlates with fluvial forces in areas that experienced erosion while channel areas of extensive deposition are more closely tied to a decrease in valley-bottom confinement. Bank erosion was greatest in areas immediately downstream of tributaries capable of delivering coarse sediment to the channel that was mobilized during the flood exposing previously protected cutbanks to flood hydraulics. Results indicate that the impulse framework may be a useful tool for investigations of geomorphic change resulting from floods
