Approach to Digital Elevation Model Correction by Improving Channel Conveyance

Digital elevation models (DEM) are important inputs for topography in modeling floods for remote and inaccessible regions. DEMs often lack in accuracy near water bodies and rivers. The objective of this research is to present a DEM correction technique to improve the accuracy of flood simulation and inundation mapping. The key feature of this method is the variability in thalweg (deepest point along a cross section) locations and depth based on the river meandering, width, and side slope. The DEM correction technique is demonstrated by adjusting a national elevation dataset (NED) DEM along the Cumberland River near Nashville in Tennessee. The original (base DEM) and modified DEMs are used as main input of the 1D Hydrologic Engineering Center River Analysis System (HEC-RAS) model and corresponding performances were analyzed. The model using surveyed topography was calibrated for a high flood event (May 2010) and later validated for an intermediate flood event (2003), a high flood event (May 2010), and a low flood event (May 2013) using the modified DEM. It was found that the model with base DEM is capable of simulating at a very high stage but fails during low and intermediate stages. The applicability of base DEM is also limited for any event above 127m and 3,000m3/s with specific biases. The model using modified DEM could be used for simulating large arrays of flow events. The root mean square error (RMSE) for simulated stage using modified DEM for 2003, 2010, and 2013 with the observed stage were 0.86, 0.23 and 0.52m respectively. Comparison of simulated flood map for the May 2010 flood event using modified and base DEMs with observed flood extent showed errors of 2.66% (overestimate) and 13.38% (overestimate), respectively. The preliminary application of the DEM correction technique thus showed significant improvements in the quality of DEM data with corresponding increase of the HEC-RAS model accuracy.