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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 Rhine as Europe’s most important waterway is navigable for about 800 km. Over centuries, it has experienced numerous human interventions along this length, from barrage construction in the upper part, through river straightening and regulation, and implementation of flood defence measures along most of its course, to land reclamation in its delta, to name just a few. The large number of changes brought along major environmental issues, namely an overall tendency to insufficient sediment amounts, widespread loss of habitats and biodiversity, and the sensitivity to flooding. Nowadays, the Rhine is an intensively managed river with important industries along its banks and a highly cultivated and densely populated catchment and delta. It is therefore a fundamental challenge to reach an agreement between its role as a waterway, the manifold of other human uses and environmental demands, to improve its ecological condition.From its last barrage at Iffezheim, the Rhine is free-flowing and crosses the border between Germany and the Netherlands after about 530 km, where it soon connects with the Meuse to form the Rhine-Meuse delta. In this setting, Dutch and German partners take a new approach to address urgent issues on a transboundary level. As part of the pan-European research infrastructure DANUBIUS-RI, two natural laboratories, called the Middle Rhine Supersite (GER) and the Rhine-Meuse Delta Supersite (NL), are being set up to facilitate interdisciplinary research on questions regarding system understanding and ecological improvement of the river to foster the identification of possible solutions. DANUBIUS-RI, the “International Centre for Advanced Studies on River-Sea Systems”, is being developed with the goal to support interdisciplinary and integrated research on river-sea systems. It aims to enable, support and bring together research addressing the conflicts between societal demands, environmental change and environmental protection along the continuum from freshwaters to marine waters, by providing easy access to a wide range of fundamental and comparable data from a diverse set of European river-sea systems. It will also facilitate physical access to these systems through multiple supersites.A first pilot project at the Rhine, supported by INTERREG regional funding of the Euregio Rhine-Waal, involves partners of both the Dutch and the German supersite and focuses on the comparison of sediment measurement and data processing methods in both countries. The goal of this ‘Living-Lab Rhine’ (LILAR) project is to enable a better transboundary use and comparison of the data to eventually improve the overall understanding of the Rhine sediment regime and to strengthen the transboundary efforts regarding sediment measurements and potentially even river management between Germany and the Netherlands.

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.

Identifying sources and fluxes of suspended matter within the catchment is vitally important for the water quality of rivers and for establishing sediment management plans. Constituents of suspended particles are of abiotic and biotic origin. In the Elbe, the biotic fraction of suspended particles is mainly composed of phytoplankton biomass. In this study, total seston and phytoplankton are analyzed for their seasonality, their interdependence and temporal trends over three or five decades, respectively. The biotic load was separated from the total suspended matter load, and time series of total suspended substances (seston) (1964 to 2015) and chlorophyll a values (1985 to 2015) were analyzed. Our analyses focused on the seasonal dynamics, long-term trends, and the correlation to hydrological events. The mean share of phytoplankton in total seston accounted for 24% in summer months (April–September), with a negative correlation between discharge and total seston, and 11% in winter months (October–March), with a weak positive correlation between discharge and total seston. The long-term trend of seston load was decreasing, while phytoplankton load did not show a significant trend. Autochthonous biogenic portions should not be neglected in the budget of total suspended matter loads in the Elbe catchment. Our results indicate that land-use and industrial changes subsequent to the German reunification mainly caused the observed trend. Phytoplankton growth superimposes the seasonal dynamics of seston in summer, whereas in the long term, decreasing mineral fraction dominates the significantly decreasing trend.

Understanding the dynamics of settling, consolidation and remobilization of cohesive and contaminated sediment is an important requirement to assess the risk of erosion and to manage mud-dominated ecosystems. Here, we present data on the erodibility of cohesive sediments from the impounded Upper Rhine River and develop a modelling concept to understand the suspended sediment dynamics along the impounded Upper Rhine. The conceptual framework includes 10 reservoirs of the Upper Rhine between Basel and Iffezheim, which serve as long-term sinks of cohesive sediment. Each reservoir is represented by a 1D sediment budget model, which is coupled to its upstream and downstream neighbour. In this paper, we focus on the uncertainty associated with the measurement of the erodibility of cohesive sediments and on the implications to model the risk of erosion. The statistical analysis showed a large uncertainty of the estimated critical shear stresses and erosion rates. Root mean square errors are in the order ...

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 applications of remote sensing in hydrology are diverse and offer significant benefits for water monitoring. Up to now, operational river monitoring and sediment management in Germany mainly rely on in-situ measurements and on results obtained from numerical modelling. Remote sensing by satellites has a great potential to supplement existing data with two-dimensional information on near-surface turbidity distributions at greater spatial scales than in-situ measurements can offer. Within the project WasMon-CT (WaterMonitoring-Chlorophyll/Turbidity), the Federal Institute of Hydrology (BfG) aims at the implementation of an operational monitoring of turbidity distributions based on satellite images (esp. Sentinel-2, Landsat7 and 8). Initially, selected federal inland and estuarine waterways will be addressed: Rhine, Elbe, Ems, Weser. WasMon-CT is funded within the German Copernicus activities. Within the project, a database of atmospherically corrected, geo-referenced turbidity data will be assembled. The collected corresponding meta-data will include aspects of satellite data as well as hydrological data, e.g. cloud cover and river run-off. Based on this catalogue of spatially linked meta-data, the satellite data will be selected by e.g. cloud cover or run-off. The permanently updated database will include past as well as recent satellite images. It is designed with a long-term perspective to optimize the existing in-situ measurement network, which will serve partly for calibration and partly as validation data set. The aim is to extend, but not to substitute, the existing frequent point measurements with spatially extensive, satellite-derived data from the near surface part of the water column. Here, turbidity is used as proxy for corresponding suspended sediment concentrations. For this, the relationship between turbidity and suspended sediment concentrations will be investigated. Products as e.g. longitudinal profiles or virtual measurement stations will be developed from an application toolbox to specifically match requirements of operational monitoring tasks and to allow for a better integration into the existing monitoring system. The toolbox demonstrates the benefits of remote sensing by applying the established processing chain to diverse hydrological questions, such as for the investigation of tidal-affected sediment loads or mixing processes at river confluences. This new application will be of great value to assess, evaluate and monitor the status or the change of large-scale sediment processes at the system level. Accordingly, the satellite-derived turbidity data will strongly enhance federal consulting activities and thus ensure a modern river monitoring of Germany’s federal water ways.

Recently amended European (EU) water policies call for an adequate monitoring of the chemical status of sediments and suspended matter (SM) in rivers. In this study, we focus on long-term time series of particle-bound hexachlorobenzene (HCB) and selected polychlorinated biphenyls (PCB-138 and PCB-153) that were monitored biweekly to monthly at eight stations in the River Rhine catchment. Our aims are (1) to detect trends in the concentration series HCB, PCB-138 and PCB-153, (2) to estimate the uncertainty of loads caused by SM collection techniques and load calculation procedures and (3) to detect trends in the subsequently calculated annual load series. HCB concentration in the SM for the period 1995–2008 significantly (p < 0·01) decreased at six of the eight monitoring stations. Decreasing PCB-138 and PCB-153 concentrations are significant at six of the eight and seven of the eight monitoring stations, respectively. A two-way analysis of variance (ANOVA) that tested the effect of two collection techniques and four load calculation procedures on annual loads indicates homogeneity of the methods at four of the five monitoring stations. At Weil, only the loads of HCB, PCB-138 and PCB-153 are significantly affected by the collection technique. The trend analysis of an extended series (1985–2007) of annual HCB loads at Koblenz showed a significant decrease from about 110 kg year−1 to about 15–23 kg year−1; however, in the shorter period (1995–2007) only at two of the eight monitoring stations decreasing trends of annual contaminant load could be detected. We conclude that any of the tested load calculation procedures can be applied, as loads do no differ systematically. Although a high uncertainty in load estimation exists (e.g. maximum percentage error of E = [18·1, 122·5]% for HCB), the monitoring programme at the Rhine is adequate for analysing the long-term chemical status of SM. Copyright © 2011 John Wiley & Sons, Ltd.

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.

Mitteilungen / BfG – 30.2014 - ISSN 1431-2409 - ISBN 978-3-940247-10-0

This study focusses on the effect of sampling techniques for suspended matter in stream water on subsequent particle-size distribution and concentrations of total organic carbon and selected persistent organic pollutants. The key questions are whether differences between the sampling techniques are due to the separation principle of the devices or due to the difference between time-proportional versus integral sampling. Several multivariate homogeneity tests were conducted on an extensive set of field-data that covers the period from 2002 to 2007, when up to three different sampling techniques were deployed in parallel at four monitoring stations of the River Rhine. The results indicate homogeneity for polychlorinated biphenyls, but significant effects due to the sampling techniques on particle-size, organic carbon and hexachlorobenzene. The effects can be amplified depending on the site characteristics of the monitoring stations.