Assessing the effect of different bathymetric models on hydraulic simulation of rivers in data sparse regions.

• River bathymetry affects various flood inundation outputs differently. • Cross-sectional area, and not the channel shape, is critical to hydraulic modeling. • Both channel area and thalweg are important for velocity and shear estimates. • Simplified geometries can be used for reaches with small sinuosity, width or depth. River bathymetry, which is vital for accurate hydraulic modeling, is not readily available at large scales because of the logistical difficulties in field surveys and uncertainties associated with remote sensing techniques. Several studies have explored the potential of conceptual models and interpolation algorithms to estimate bathymetry. These models have certain underlying assumptions that limit their accuracy and widespread implementation. This study aims to provide insights into the choice of bathymetric model for different hydraulic applications by analyzing the effect of different bathymetric models on hydraulic modeling under different geomorphologic and flow settings. This study does not aim to reinforce the importance of bathymetry, rather its objective is to identify the bathymetric properties that are critical to accurate estimation of different hydraulic outputs. The study accomplishes its objectives by implementing three different bathymetric models with varying cost and efficiency at four sites with diverse bathymetric characteristics. Five hydraulic outputs, namely wetted cross-sectional area, water surface elevation, inundation extents, velocity and shear are estimated at three characteristic low and high flows and the results from the four sites are grouped together to perform an unbiased and robust evaluation. The performance of these models is evaluated using the best available bathymetric representation generated from detailed field surveys as a benchmark. The results indicate that 1D flood modeling is somewhat insensitive to channel shape as long as the estimated shape reflects the channel storage accurately. Velocity and shear related applications should incorporate bathymetry that represent both the cross-sectional area and channel thalweg accurately. Reaches with low sinuosity (<1.5), or small width and depth can be modeled reasonably using simple geometric shapes, whereas for larger streams, interpolation of surveyed data along the thalweg or complex bathymetric models that account for river anisotropy, are recommended. [ABSTRACT FROM AUTHOR]