Analyse vaarweg Rijn grensregio : morphological modelling - version 1.0

This study was commissioned by the working group of Rijkswaterstaat and WSV that advises on the maintenance of the waterways in the Rhine in the Dutch and German border region. This working group was erected in 2018 and is also known as “Grensproject”. The focus of this study is on the navigability of the Rhine and its branches in the Dutch and German border region (Niederrhein–Boven-Rijn), including the upper river sections of the Waal and Pannerdensch Kanaal - Nederrijn downstream of the Pannerdensche Kop bifurcation. To ensure safe and sustainable passage of ships in these rivers, the agreed navigation-channel dimensions at OLR/GLW must be guaranteed for the coming decades along the Rhine corridor. Since the riverbed in the Niederrhein upstream of the border is stable, the most relevant approach for this study is to design measures that stabilize the eroding sections of the Dutch Rhine branches in order to stop decreasing water depths at OLR/GLW conditions in the fairways. Meanwhile, even under “stable” conditions, the bed and its composition dynamically respond to discharge fluctuations. The purpose of this modelling study is to provide a quantitative prognosis of the impacts of ongoing erosion and shifts in discharge distribution at the bifurcations under different scenarios: (1) if no measures are taken, and (2) when alternatives involving only sediment nourishments, only structural measures, or a combined strategy are implemented. The model used is an upgraded version of the original DVR model for Rhine morphology, based on the Delft3D modelling system. It covers the full study reach and simulates non-uniform sediment and varying discharges. “DVR” refers to Duurzame Vaardiepte Rijn (“Sustainable Fairway Rhine”), a project that has modelled Rhine morphology and sediment management for navigation channels over the past 20 years. The same model is also used in a parallel study for the Room for the River 2.0 programme (RvR2.0), which explores measures to prepare the Dutch Rhine branches for the future. The interpretations of the effects of measures from this study have been used in the RvR2.0 programme and vice versa. To account for climate-change impacts on river morphology, the discharge hydrographs for different climate scenarios have been analysed. For long-term simulations in this study, dry and wet discharge series from the far-future climate scenario defined by BAW (Bundesanstalt für Wasserbau) for the Niederrhein have been used. For both series, dedicated representative stepwise hydrographs repeated annually over a 30-year simulation period have been designed. These series cover the range of near- and far-future scenarios considered relevant for river morphology. Middle-high Rhine discharges (between 1,400 and5,000 m³/s) are most influential for morphological trends and the impact of measures in the Rhine and his branches.