Modeling Sandbar Morphodynamic Response to River Hydrographs: An Empirical Approach Using Landsat TM Imagery

Abstract:

Sandbars in sand-bedded rivers of the Central U.S. are highly dynamic, with substantive changes occurring across a wide range of temporal and spatial scales. River hydrology is the primary driver of channel patterns and morphodynamics in these systems, and characterization of sandbar responses to varying flow regime allows for a better understanding of landscape-scale ecology for sandbar-dependent species. We are developing models of sandbar response to river hydrology to be used initially in a metapopulation ecological model of the endangered Interior Least Tern (Sterna antillarum) for 11 different predominantly regulated rivers of the Central U.S. plains. The model is being developed to simulate long term (>30 years) species population dynamics. Because of the large temporal and spatial scope of this effort, we are using an empirical approach to characterize dynamics of sandbar location and extent within the modeling domain in place of more intensive physical models. We developed a dataset of in-channel land cover classifications spanning from 1982 to 2011 for the modeling domain using surface reflectance data from select images of the Landsat Thematic Mapper (TM) Climate Data Record (CDR). Additionally, we segmented all rivers into lengths with approximately uniform discharge and compiled historic discharge data for each segment. We integrated these data to develop a long-term dataset of sandbar area, cover type, and prevailing discharge. We used residuals of regressions between sandbar area and discharge to normalize sandbar area to varying discharge. By comparing our sandbar area and vegetation cover dataset to historic discharge records, we characterize the types of hydrographs that form, erode, and recruit vegetation on sandbars in different river systems, and the rates at which these processes occur. Additionally, we use geomorphic covariates calculated from remote sensing data to begin to explore controls on spatial variation in sandbar morphodynamics.