ABSTRACT
Knowledge about the hydraulics in alpine torrents is relevant to quantify flood risks, to study sediment transport and to assess the water-bodies ecology. Usually, Computational Fluid Dynamics (CFD) simulations are the preferred tool to calculate velocities, water depths and sediment transport for the discharges of interest, which then serve as a basis for the evaluation of flood risks or ecological conditions. To enable reliable calculations, high-quality terrain data of the riverbeds, riverbanks, and floodplains are required. Typically, DTMs of the floodplains reconstructed from airborne light detection and ranging (LiDAR) data are combined with terrestrial surveys of riverbanks and riverbeds. The terrestrial surveys are necessary as the lasers usually cannot penetrate the water surface in the observed water-bodies. They are labor intensive and can be located in difficultly accessible terrain. Therefore, data of the riverbeds’ and riverbanks’ geometry is hardly available at such a high resolution and extent that is comparable to the airborne LiDAR based data of the floodplains. In this study a newly available airborne water-penetrating LiDAR system was used to survey alpine torrents. Detailed and extensive data of riverbeds and riverbanks were acquired. The general applicability of the data as a basis for a Telemac-2D simulation was investigated. Mesh creation based on breaking edges or on a downsampled point cloud are shown. Finally, a calibration was done based on abundant water surface points stemming from the airborne-laser scanning. The LiDAR data turned out to be a very suitable data source for constructing the computational grids of the riverbed. The CFD results showed new possibilities in the comparison of measured and simulated water heights.
