Damage costs due to bedload transport processes in Switzerland

Abstract. In Alpine regions, floods are often associated with erosion, transport and deposition of coarse sediment along the streams. These processes are related to bedload transport and pose a hazard in addition to the elevated water discharge. However, it is unclear to what extent they contribute to total damage caused by natural hazards. Using the Swiss flood and landslide damage database – which collects financial damage data of naturally triggered floods, debris flows and landslides – we estimated the contribution of fluvial bedload transport processes to total damage costs in Switzerland. For each database entry an upper and lower limit of financial losses caused by or related to bedload transport processes was estimated, and the quality of the estimate was judged. When compared to total damage, the fraction of bedload transport damage in the 40 yr study period lies between 0.32 and 0.37. However, this value is highly variable for individual years (from 0.02 to 0.72). Bedload transport processes have induced cumulative financial losses between CHF 4.3 and 5.1 billion. Spatial analysis revealed a considerable heterogeneous distribution with largest damage for mountainous regions. The analysis of the seasonal distribution shows that more than 75% of the bedload damage costs occurs in summer (June–August), and ~ 23% in autumn (September– November). With roughly 56%, by far most of the damage has been registered in August. Bedload transport processes are presently still inadequately understood, and the predictive quality of common bedload equations is often poor. Our analysis demonstrates the importance of bedload transport as a natural hazard and financial source of risk, and thus the need for future structured research on transport processes in steep streams.