Comparison of bathymetric data sources used in hydraulic modelling of floods

Topographic data plays an essential role in hydraulic modelling of floods. A high-precision digital elevation model (DEM) including river bathymetry (bed topography) is required. DEMs can be derived from such various data sources as ground surveying or remote sensing techniques. This study is focused on (a) the DEM error that results from the inability to scan the morphology of the channel using remote sensing methods, and (b) assessment of its impact on the results of a one-dimensional (1D) hydraulic model. DEMs produced by remote sensing techniques were tested in combination with ground surveying and by software-updated remote sensing data. Differences in riverbed representation and thalweg position were evaluated. The 1D hydraulic model HEC-RAS was chosen to determine the impact of various DEM sources on the hydraulic quantities (water surface elevation, inundation area). The study was carried out on a reach of the River Vltava (Czech Republic). The best results were achieved by DEMs that combined remote sensing data with ground mapping. Good results also were obtained using software-updated remote sensing data. Neglecting of cross-sectional area in remote sensing data has an important impact on the results of hydrodynamic models.