Transnational concept for the provision of streambank erosion hazard information

Streambank erosion is an aspect of flood hazards that has been largely neglected to date due to its complexity. The INTERREG IIIb NWE project « Strategies and Actions for Flood Risk Management » (SAFER) has recognized its importance by including this aspect in the flood hazard component of the project. SAFER promotes integrated flood management by developing strategies for flood hazard mapping, flood partnerships and flood emergency management. These strategies are transnational due to the cooperation of partners from different geographical and administrative regions in their development. A transnational strategy for streambank erosion hazard mapping is developed. The demand for streambank erosion hazard information is listed so as to better develop the methodology with the end-user in mind. The methodology involves a regional model useful for prioritizing regions for more detailed analysis. The regional model consists of confronting calculated river shear stresses (via modelling or simplified formulas) with areas of high vulnerability. River reaches with the greatest conflicts can then be analyzed further. Geomorphological mapping is necessary before any further modelling can be done. It will permit an understanding of the sediment movements in the river catchment. The next step is to do detailed streambank erosion modelling with a geofluvial model that combines hydrodynamic, sediment transport and geotechnical modelling. The model CCHE1D of the National Center for Computational Hydroscience and Engineering of the University of Mississippi is adapted in the SAFER project for the detailed modelling. The adaptation is very significant because it provides a 1D model that can be applied to a meandering river reach of tens of kilometres. Data needs for regional and detailed modelling procedures are listed. The streambank erosion hazard mapping methodology was developed on the Venoge River in Switzerland and applied to the River Enrick in Scotland and the Lauter River in Germany. Streambank erosion monitoring on the Venoge River allowed for data collection techniques to be considered with respect to streambank erosion modelling. It also provided data for testing the adapted CCHE1D model. Streambank erosion danger maps were produced in accordance with Swiss criteria that classify the danger level according to the combination of the event frequency and magnitude. Shear stress maps as necessary in the regional modelling were produced for the Lauter River. These maps were rapidly produced from the channel geometry and hydraulic information from previous flood inundation studies. Observed erosion areas coordinate well with high shear stress areas. Shear stress and erosion maps were also produced for the River Enrick. This river permitted the testing of the CCHE1D model for streambank erosion hazard mapping in the case of a steep river with a high sediment load. The model permitted the calculation and mapping of the shear stresses and erosion for the historical period of 1993-2004 and for design flows. The River Enrick modelling showed the necessity of further research in modelling and methodological procedures for braiding areas. Application of the SAFER streambank erosion methodology to these three varied river settings permitted the development of a transnational strategy.