Determination of runoff and sediment transport in an Alpine torrent in Austria

Floods including sediment transport are a significant threat to  communities in Austria. With climate change impacting the Alps, it is crucial to enhance and reassess protective measures. Predictions for the future of the Alpine climate indicate that there will be more winter precipitation and stronger, convective rain in the summer, even if the temperature goals set by the  Paris Agreement are met.

However, analyzing the impact of increased extreme precipitation on flood events in small Alpine catchments remains a challenge, and knowledge of the subsequent impacts on sediment transport is still insufficient. The catchment area of the Schöttlbach and thus the town of Oberwölz (Murtal, Styria) were affected by extreme flood events with extreme sediment transport in both 2011 and 2017, which caused heavy damage. The region was therefore selected to work with local stakeholders (especially the Austrian Torrent and Avalanche Control authorities) to improve the process understanding of flood events and sediment transport in a torrent catchment area and to draw possible climate change scenarios for the future.

It was the aim of the project „RunSed-CC“ (i) to estimate future runoff and sediment transport in an Alpine catchment using the latest climate projections (ÖKS15), (ii) to consider them in the light of the associated model uncertainties, and (iii) the potential for extrapolating the results to other Alpine catchments to test.

One focus of the project was the collection of natural data using a wide variety of measurements in the catchment area of an alpine torrent.The project RunSed-CC developed further a model that connects rainfall and runoff to sediment transport. The  hydrological model WaSiM was used, in combination with data on the  evolution of sediment source areas, to drive the 2D numerical models Telemac-2D (hydrodynamics) & Sisyphe (sediment transport). The main focus of the project was to  understand the potential impacts of future climate change on the  hydrologic regime, changes in sediment dynamics and sediment yield, and  associated uncertainties in the model.

This article is intended to provide a brief outline of the results of the extensive project, with a focus on the final findings of the sediment balances at the outlet of the catchment area.