Flood-prone area delimitation using UAV technology, in the areas hard-to-reach for classic aircrafts: case study in the north-east of Apuseni Mountains, Transylvania

In the delimitation of flood-prone areas, particularly in areas that are difficult to access using traditional flight equipment, the most critical problem is the generation of a high-quality DEM of the major and minor riverbed, in order to obtain several hydraulic parameters (e.g., the surface of the drainage section, average water velocity) with equivalent accuracy. The chosen area for the case study represents one with the greatest history of hydrological risk factors in the SomeAYul Mic basin, given the extreme previous hydrological events that have taken place (e.g., in the year 1995) as well as the limited capacity of the river for upstream river flow, and to handle the volume of the flash floods. In this study, the use of UAV technology coupled with Leica MultiStation for validation made it possible to achieve this performance. Another advantage was the existence of the hydrometric station situated in the middle of the study area, the information from which was used for statistics, calibration of the measurements and validation of the results obtained (roughness of the riverbed, the debit with an overflow possibility). The hydraulic calculations performed on the 11 transverse profiles, conducted using the GIS terrain model, led to the high accuracy defining of the flood-prone areas corresponding to the flows in the major riverbed with probabilities of 1 and 5 %. Also highlighted on the 2D and 3D images were several civilian areas at risk in the case of extreme hydrological events, related to maximum flow.