Knowledge about the hydraulic situation in a mountain torrent is relevant to quantify flood risks, to study sediment transport and to assess the waterbodies’ ecology. To conduct reliable calculations, high-quality terrain data of riverbeds, riverbanks and floodplains are required. Typically, digital terrain models (DTMs) of floodplains are derived from classical airborne laserscanning (red wavelength) together with terrestrial surveys along riverbeds and riverbanks. Usually these are restricted to a limited number of cross sections. The terrestrial surveys are necessary because those laser systems cannot penetrate through the water column of the observed waterbodies. Consequently, data for the geometry of riverbeds and bank structures are hardly available at a high spatial resolution and extent, comparable to the airborne-laser scanning derived data for river floodplains. In this study, a newly available, water-penetrating airborne laser system (green wavelength, FFG research project between the University of Innsbruck and Riegl LMS) was used to survey a mountain torrent. Detailed and extensive data (~ 30 points/m² on topobathy side) of the riverbed, the riverbanks and the neighboring floodplains were acquired with this single sensor. The general applicability of such hydromapping data as a base for 2D-and 3D numerical simulations was investigated. For this, a detailed analysis was carried out by comparing results of 2D-calculations based on the new hydromapping data and 2D-calculations based on traditional terrestrially measured cross-sections. For example, the morphologic boundary conditions are significantly better defined when using the hydromapping data than they are when using cross-sections. This is already due to the original high spatial resolution and spatial data coverage of the hydromapping data, which saves the need of any interpolation, required when using cross-sections that can be tens to hundreds of meters apart from each other. Hydromapping delivers the entire structure of a riverbed and therefore a geometrical information about its friction.