UAV and TLS for monitoring a creek in an alpine environment, Styria, Austria

Flood events often endangered and damaged the small town of Oberwolz (Styria, Austria) and its nearby surroundings. In 2011 the last bigger flood occurred. After that, the main watercourse, the Schottlbach creek, became a centre of a national funded research project. A wide variety of methods were applied together with intraand extra-universitarian project partners to investigate that creek from a fluvial-geomorphological point of view. Apart from hydrological, meteorological, and geophysical methods, both, terrestrial and airborne remote-sensing techniques were applied. In particular, terrestrial laser scanning data as well as terrestrial and aerial photographs were frequently recorded since 2012. On the one hand the terrestrial monitoring focused on some representative erosion sites to quantify detailed erosion rates. On the other hand recording the sediment catchment output at the flood detention basin was intended. The aerial-based monitoring included three flight campaigns using mainly a fixed-wing unmanned aerial vehicle to cover approximately an area of about 170 ha that corresponds roughly to the major parts of the Schottlbach creek. The main focus of the study lies on the adequate processing, georeferencing, and qualitative and quantitative comparison of the recorded elevation data. This was primarily done by using structure from motion photogrammetry and geodetic measurements. The resulting point clouds, digital elevation models, and orthophotos allow a visualization and quantification of morphodynamic processes. As a main outcome of this study, the combined usage of the mentioned methods can be seen. In this way, data recording from diverse perspectives is possible and allows a consideration of the varying terrain inclination. In addition, the significance of the resulting data for a geomorphological interpretation was assessed by describing the uncertainties. Beyond that, this methodology meets the need for observation at different scales.