During a flood event alpine watersheds not only discharge water but a considerable amount of sediment. For a comprehensive flood protection concept runoff and sediment transport need to be simulated together.
Mass-Balances of Alpine Catchments – Rainfall/Runoff- and Bedload Transport Modeling Using PROMAB-GIS
For practical flood-hazard assessment in ungauged torrential catchments the use of simple empirical formulae is common. These however cannot normally take site-specific characteristics, like spatially-distributed soil types, vegetation cover, geological settings or sediment sources of the individual catchment into account. Therefore, these methods often gain rather general results which are of limited use for planning protective measures.
In the course of the project „Massenbilanzen alpiner Einzugsgebiete“, the model PROMABGIS – originally developed by Jenewein, 2002 and Rinderer, 2002 – was further improved. It is a distributed rainfall-runoff model coupled with a bedload transport module (Rinderer et al., 2010).
The runoff-generation and -concentration on the hillslopes are modelled with hydrological approaches considering spatially-distributed rainfall events. Within the channel-network the entrainment, transport as well as temporary or final deposition of sediment is modelled. Due to the fact that even during flood events unsaturated transport conditions can be dominating, the availability of material and the dissipation of energy due to form roughness are considered. Furthermore, the slope gradient of the channel is adjusted according to the amount of sediment erosion or deposition within a channel reach.
For an efficient and user-friendly workflow the pre- and postprocessing can be done via a graphical user-interface specifically programmed for the GIS-Software ArcView. The relevant model-input-parameters have to be gathered using field mapping and remote sensing techniques.
PROMABGIS is a tool for practitioners supporting them in flood-hazard assessment in alpine catchments. The model is currently in use by the engineering consultants who sponsored this project.