Effective water storage as flood protection : the Rijnstrangen study case

Climate change is expected to cause higher discharge levels in the river Rhine at the Dutch-German border. In this study group project that was commissioned by Rijkswaterstaat, we investigate the possibility of flooding the Rijnstrangen area as a protective measure. We identify three subproblems. We first analyze the data recorded by Rijkswaterstaat and estimate the likelihood and the duration of extremely large discharges at the German border into the river. Next, we investigate how a change in discharge levels affects the water height in the first 35 kilometer section in the Netherlands. Finally we study the design of weirs and floodgates to allow diverting a sufficiently large amount of water flow from the river into the retention area. Our statistical analysis shows that an extreme discharge level is expected to occur once every 1250 years and to last for about three and a half days. Our numerical flow model shows the water height reaches equilibrium on a time scale that is much smaller than the one on which flooding occurs. The flow can thus be considered quasi-stationary. Passive weirs finally are shown to be too long to be feasible. Actively controlled floodgates are therefore recommended.