Author(s): S. Giehl; M.D. Bui; P. Rutschmann

Linked Author(s): Peter Rutschmann

Keywords: Dynamic bed; Hydrodynamic modelling; Inn River; Morphodynamic coupling; Flood protection

Abstract: Using an equilibrium bathymetry for a hydrodynamic numerical model of the Inn River can yield consistent results for flow discharges. A coupling with a morphodynamic model is proposed to get a better prediction of water elevations. Hydro-morphology of the natural Inn River was characterised by its Alpine basin including glaciated sub-catchments in Switzerland and Austria. However, due to river training and construction of hydropower plants (HPP), the river has almost lost its original hydro-morphologic characteristics, especially along the German river reach. As an example, due to the channelization since the beginning of the 19th century, the former river floodplains were densely populated and lost their inundation areas for the most part. In the absence of vast floodplains for natural retention, the flood wave attenuation is limited along the approximately 200 km German reach up to the confluence with the Danube. Only around 28 km river stretch kept its free flow characteristics. Furthermore, the river receives a high transport rate of sediments from its alpine (glacial) catchment. However, a significant amount of the sediments is trapped in the HPP reservoirs. In the German river reach, the sediments consist of fine particles with a median diameter of 0.3 mm, which leads to highly dynamic bed level changes during flooding periods. Flood events in the river are induced by short but heavy rainfall in summer. In the impounded sections, the bed erosion increases during the rising limb of major flood hydrographs causing significantly lower bed levels at the wave peaks. After that, the transported sediments are deposited again. As a consequence, the available bathymetry, which has been measured regularly but not during flood events, cannot fully represent the bed topography during the peak discharge. To protect the population along the river there are plans for enhanced flood protection systems including for instance controlled lateral retention basins as well as relocation of dykes and restoration of floodplains. An extensive study is been carried out to analyse the effect of the possible measures on flood waves under several hydrological scenarios with the help of multidimensional hydro-morphodynamic numerical modelling. This paper presents a part of the results obtained from a 2D hydrodynamic model for studying the effect of bed-level changes on the hydrodynamic results, which could help to reduce the uncertainties in the hydrodynamic simulations arising from morphological changes.

DOI: https://doi.org/10.3850/978-981-11-2731-1_352-cd

Year: 2018