The aftermath of “Room for the River” and restoration works: Coping with excessive maintenance dredging

Abstract In the 19th and early 20th centuries, the Rhine in the Netherlands has been heavily trained for the purpose of safe discharge of water, sediment and ice, and a better navigability. Currently a large number of new river intervention works are planned and built within the Room for the River Program (RfR) and the European Water Framework Directive (WFD). The measures increase the flood conveyance capacity as well as biodiversity. Popular measures are dike setback, lowering flood plains, reconnecting side channels and removal of bank defences. Improving conditions for inland navigation has not been a design criterion in these RfR and WFD projects. River intervention based on RfR and WFD design principles is not totally unique for the Netherlands. Examples can also be found elsewhere in the world, i.e. in China, in USA, in Colombia and elsewhere in Europe. River intervention works based on the RfR and WFD design principles turn out to have a strong impact on flow and sediment transport fields, and induce larger dynamics of the riverbed. This negatively influences the river's navigability. As a consequence maintenance costs for navigation are expected to rise. Moreover, the intended dredging operations will hamper inland navigation significantly, resulting in large economic impacts and a lower safety of inland navigation. This paper illustrates the potential of a stochastic approach to assess maintenance dredging and navigability, before and after execution RfR intervention works. A 2D morphological model is used in a deterministic and stochastic setting using Monte Carlo Simulation, and the merits of a stochastic approach with respect to a deterministic approach are illustrated. The authors give recommendations for river training works that could be jointly considered with RfR intervention works, in order to avoid excessive maintenance dredging and create a river system that keeps itself navigable: so self-supporting.