Twin storms and the performance of storm surge barriers

Early 2022, four severe storms (Corrie, Dudley, Eunice and Franklin) raged over the Netherlands, of which the latter three hit the Dutch coast in only four days. The question is how well the Dutch flood protection system can deal with such a series of storms. Will there be enough time to recover from the previous storm?

The Maeslant barrier is a storm surge barrier near Rotterdam that exists of two enormous floating sector doors. In rest, they are safely located in the dry docks along the shore. Yet, in case of the most severe storms the doors are floated to the middle of the river and submerged to retain storm surges from the sea. After the storm they are floated up again and moved back to the docks. During its operation the Maeslant barrier is likely to be more vulnerable for small damages, that may lead to the temporal unavailability of the surge retaining function.

This study investigates 1) the probability that the barrier needs to close shortly after a previous closure and 2) the flood risk as a result of failure of the second closure. Herewith, we distinguish two different phenomena. The two-top storm is a single storm during which the barrier needs to close twice and open in between as a result of the astronomical tide. The twin storm (or even triplet or multiple storm) is a cluster of severe storms that succeed each other shortly.

The probabilities of both phenomena are estimated from a data-analysis of a long record of sea level observations at Hoek van Holland, close to Rotterdam. The associated flood risk is estimated from a simple conceptual model of the failure probability of the Maeslant barrier.