Development of a methodology to assess future functional performance of a river system

The summer and autumn of 2018 showed the negative drawback of both low-flow conditions and bed degradation over the last century in the Dutch Rhine. This resulted in record-breaking low water levels, extreme low navigation depth and subsequently nautical problems. The Rhine’s long-term bed degradation is the response to river training of the last centuries focused on improvement of navigation and flood protection. Over the past hundred years the river bed of the Upper Dutch Rhine branches degraded 1 to 1.5 m, while a current trend of 1 to 2 cm per year is observed (Blom, 2016). The ongoing bed degradation is problematic since it induces (i) a reduction of navigation depths due to the existence of non-erodible layers, (ii) lowering of ground water levels and dehydration of nature, (iii) lowering of coverage rates of infrastructure (e.g. cables in subsoil, bridges and groynes) and (iv) a gradual shift in discharge distribution at the bifurcation points. As climate change will increase the inter-annual variability of the Rhine’s discharge pattern, low-flow conditions are likely to occur more often, reinforcing the abovementioned impacts on nature and navigation (Sperna Weiland et al.,