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Heavy rainfall is the main driver of soil erosion by water which is a threat to soil and water resources across the globe. As a consequence of climate change, precipitation – and especially extreme precipitation – is increasing in a warmer world, leading to an increase in rainfall erosivity. However, conventional global climate models struggle to represent extreme rain events and cannot provide precipitation data at the high spatio-temporal resolution that is needed for an accurate estimation of future rainfall erosivity. Convection-permitting simulations (CPS) on the other hand, provide high-resolution precipitation data and a better representation of extreme rain events, but they are mostly limited to relatively small spatial extents and short time periods. Here we present for the first time rainfall erosivity and soil erosion scenarios in a large modelling domain such as Central Europe based on high-resolution CPS climate data generated with COSMO-CLM. We calculate rainfall erosivity for the past (1971–2000), present (2001–2019), near future (2031–2060) and far future (2071–2100) and apply the new data set in the soil erosion model WaTEM/SEDEM for the Elbe River basin. Our results showed that future increases in rainfall erosivity in Central Europe can be up to 84 % in the river basins of Central Europe. These increases are much higher than previously estimated based on regression with mean annual precipitation. In consequence, soil erosion and sediment delivery in the Elbe River basin are also increasing strongly. Locally, changes in erosion rates can be as high as 120 %. We conclude that despite remaining limitations, convection-permitting simulations have an enormous and to date unexploited potential for climate impact studies on soil erosion. Thus, the soil erosion modelling community should follow closely the recent and future advances in climate modelling to take advantage of new CPS for climate impact studies.

The purpose of the current study was to present a 3D CFD model that can be used to predict long-term (11 years) bed changes in a reservoir due to sedimentation and dredging. And that this can be done with a reasonable computational time (18 hours) on a desktop computer. The numerical model solved the Navier-Stokes equations on a 3D non-orthogonal unstructured grid to find the water velocities and turbulence. The convection-diffusion equation for suspended sediment transport was solved to find the sediment deposition pattern. Bed changes were computed and used to adjust the grid over time. Thereby, bed elevations over time were computed. The effect of dreding was also included in the model, and how this affected the bed elevation changes. The main feature of the numerical model enabling a reasonable computational time was implicit numerical methods giving the possibility to use long time steps. The results were compared with annually measured bed elevation changes in the reservoir over 11 years, this gives 11 figures of bed elevation changes, due to sedimentation and dredging. Comparing the annually computed and measured bed changes, there was a fair agreement for most of the years. The match was not perfect, but the main deposition patterns were reproduced. The amount of sediments removed in three dredging campaigns were also computed numerically and compared with the measurements. Parameter tests were done for the grid size, fall velocity of the sediments, cohesion and sediment transport formula. The deviation was less than 16 % for all these four parameters. The 3D CFD numerical model was able to compute water flow, sediment transport and bed elevation changes in a hydropower reservoir over a time period of 11 years. Field measurements showed reasonable agreement with the computed bed elevation changes. The results were most sensitive to the sediment particle fall velocity and cohesion of the bed material. Long-time 3D CFD modelling of sedimentation with dredging in a hydropower reservoir This is a post-peer-review, pre-copyedit version of an article published in Journal of Soils and Sediments. Locked until 5 April 2019 due to copyright restrictions. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11368-018-1989-0.

Sediment flux of lowland rivers is dominated by suspended transport, but data is often sparse and analysis largely relies on rating relationships. However, suspended sediment concentration is by no means constant in both, space and time. Here we analyse the variability of sediment rating curves and the seasonality of suspended sediment concentration in German waterways, as recorded by 10 gauging stations with catchment areas between 2600 - 22000 km2. Our data reveal a distinct break in power-law scaling relationships for all stations, with increased scaling exponents above threshold discharges close to the geometric mean. We attribute this mainly to the activation of sediment sources that resist mobilisation at lower flows. Furthermore, all stations show a counter-clockwise hysteresis effect throughout the year, where summer discharges have a higher sediment load than comparable winter discharges. Though the reasons for this pattern need further investigation, preliminary results show a strong correlation with rainfall erosivity and land-use parameters.

The essential processes and mechanisms of the transport of contaminants from a river to a well field via a flood water retention area are presented. The transport is conceptualized as a succession of three phases: (1) contaminant entry into the retention area, (2) passage through the soil zone and (3) transport with the groundwater flow. Depending on the conditions of a given location and on the properties of the contaminants of interest, processes within each transport phase may reduce the concentration of the contaminants at the well field. For the Kastenwoert-Rappenwoert study area, the results of the described processes are shown by chemical and ecotoxicological analyses as well as by numerical modelling. Based on the results of the analyses, it is predicted that some contaminants in the study area will be completely detained along the transport path, while others will be transported as far as the well field, although in significantly reduced concentrations.