Effect of cross-section interpolated bathymetry on 2D hydrodynamic model results in a large river

Two-dimensional (2D) hydrodynamic models have been increasingly used to quantify aquatic habitat and stream processes, such as sediment transport, streambed morphological evolution, and inundation extents. Because river topography has a strong influence on predicted hydraulic conditions, 2D models require accurate and detailed bathymetric data of the stream channel and surrounding floodplains. Besides collection of mass points to construct high-resolution three-dimensional surfaces, bathymetries may be interpolated from cross-sections. However, limited information is available on the effects of cross-section spacing and the derived interpolated bathymetry on 2D model results in large river systems. Here, we investigated the effects of cross-section spacing on flow properties simulated with 2D modeling at low, medium and high discharges in two morphologically different reaches, a simple (almost featureless with low sinuosity) and a complex (presenting pools, riffles, runs, contractions and expansions) reach of the Snake River (Idaho, USA), the tenth largest river in the United States in terms of drainage area. We compared the results from 2D models developed with complete channel bathymetry acquired with multibeam sonar data and photogrammetry, with 2D model results that were developed using interpolated topography from uniformly distributed transects. Results indicate that cross-sections spaced equal to or greater than 2 times the average channel width (W*) smooths the bathymetry and suppresses flow structures. Conversely, models generated with cross-sections spaced at 0.5 and 1 W* have stream flow properties, sediment mobility and spatial habitat distribution similar to those of the complete bathymetry. Furthermore, differences in flow properties between interpolated and complete topography models generally increase with discharge and with channel complexity. Copyright (c) 2013 John Wiley & Sons, Ltd.