Delta plan Netherlands

Last month the Dutch newspaper Trouw (19th September) reported on the new Dutch Deltaplan, made to counter the current water challenges. The Netherlands is facing increased river discharge, increased precipitation, and a sea level rise of about 35-85 cm, in combination with land subsidence. 

After the 1953 flood disaster safety levels of levees were calculated and levees were prepared accordingly. What was lacking consisted of maintenance (one third of the levees did not fulfill the original safety designs), and the norms were never recalculated to account for any changes, including climate change. The norms also didn't account for levee failures by droughts or by piping, where water seeps through underneath the levee. 

The new norms work differently. Rather than calculating the chance of floods, the chance of levee failure is used. Another change is to use the chance of dying from a flood rather than a flood occurrence. The new norm of acceptable safety is having a chance of 1 in 100,000 to die as a consequence of floods. The standard safety norms for other disasters such as dangerous compounds is 1 in 1,000,000. The reason floods have a higher chance is mainly that it is impossible to arrange physical infrastructure to reach the 1,000,000 safety norm. Furthermore, it is assumed that 1% of all people will drown once a polder is flooded. If the current status of the levee indicates that more people might drown, this levee is up for revision. The new Delta program calculated that over 200 levee areas will have stricter norms.

Other issues still remain, such as the traditional issue of flooding abroad. If the rivers flood in Germany, the water will enter the Netherlands not through the improved rivers, but over land unprotected by levees.