How cost effective is river widening?

The Rivers Delta Programme was completed in 2014. The aim of this programme was to develop a flood risk management strategy that reduces flood risks along the major rivers in the Netherlands and that also ensures that the new standards for flood risk management are met by the year 2050. The preferred strategy consists of a combination of strengthening dikes and widening rivers. However, as widening rivers is more expensive than strengthening dikes, questions arose about the cost effectiveness of the first. Deltares developed methods to compute two benefits of widening rivers: 1) a reduction in the costs of strengthening dikes and 2) additional risk reduction resulting from lower water levels. The ministry uses this information in a cost-benefit analysis to support their decision-making procedures about widening rivers in the next few decades.