Authors: Colin Phillips1, Jose Castejon1, Claire Masteller2, Anzy Lee1 and Belize Lane1
1Civil and Environmental Engineering and the Utah Water Research Laboratory, Utah State University, 2Earth and Planetary Sciences, Washington University in St. Louis
Title: Leveraging high-resolution topography to quantify the variable nature of river width
Abstract: During a flood the geometry of a river channel constrains the flows of water and sediment, however over many floods bankfull channel geometry evolves to reflect the long-term fluxes of water and sediment supplied by the catchment. Current predictive models correctly predict the average relationship between bankfull geometry and discharge to within an order of magnitude. However, variation about the trend has yet to be accounted for as the majority of training data are based on a few cross sections per river reach. We approach the reach scale variability issue by leveraging high-resolution lidar topography to extract continuous bankfull width measurements for 65 test cases, yielding a probabilistic description of reach-scale river width. We find that bankfull river width is well described by a lognormal distribution and varies by a factor of 2-4 at each site. The probabilistic description of bankfull river width provides an operational means for including variability within channel geometry estimates and for defining a river reach for flood mapping and routing purposes. For a given bankfull discharge, we find that the degree that a river deviates from the governing trend is positively correlated with the intermittency of the bankfull flow. We verify this finding for over 500 sites across the CONUS region and demonstrate that the bankfull intermittency is inversely related to the bankfull runoff and 30 year normal site aridity. These discoveries provide a framework for understanding how climatic or engineered (dams) changes in flow frequency and aridity could alter river geometry with direct consequences for aquatic habitat and flood risks.