ABSTRACT
In the Netherlands, the design water levels are the starting point for the calculation of the heights of the dikes In the western part, close to the sea, the design water levels depend also on wind and the sea level due to storm surges. In that part of the country, the procedure to determine the design water levels is that a large number of deterministic calculations is made with a variety of different sea levels, wind (directions and speeds) and river discharges each with a specific probability of occurrence. It is clear that the closer you get to the coast, the more important the influence of the sea level becomes (and the less important the influence of the river discharge). The most critical situation is no longer an extreme discharge (as it is far away from the tidal area), but a combination of moderate storm surge and moderate discharge. We describe a method to unravel the influence of the different stochastic variables and give suggestions to use that knowledge to define optimal measures for flood control. It is possible to use this unraveled information to design a most optimal discharge distribution along the Dutch Rhine branches in the sense that the moderate discharges are redistributed over the branches. In that way, the design water levels may be adapted on exactly those stretches where dike reinforcement is expensive. This of course means that at other locations, design water levels increase, but the measures to counteract those may be cheaper. Also, at some locations, measures to decrease the influence of the wind might be the most optimal ones.
