Hydraulic load model for the Dutch shore : Analysis about the relevance of time aspects

In recent years, KNMI, Rijkswaterstaat, Deltares and HKV have conducted a great deal of research into hydraulic loads, water levels and waves along the Dutch coast. This research has been boosted by the availability of large time series of meteorological data from the ECMWF, for which the KNMI calculated the resulting water levels on the North Sea. As a result, in total 8,000 years of simulation data have become available, for a large number of Dutch coastal stations. Compared to the limited availability of measurements for coastal stations (up to 50 or 100 years for only a limited number of stations) this long period is of great importance. It enables us to study in far more detail how wind, water levels and waves evolve in time during extreme storm surges. It becomes possible, for instance, to distinguish between short and long durations of wind and surges, and to study all kinds of correlations. This report shows the application of the prototype hydraulic load model (called ‘KustProfy’) that has been developed by Geerse et al. (2022a). The model contains time evolutions of water levels, wind and waves at four Dutch coastal stations, with associated probabilities. The model is based on the 8,000 years of simulation data, from which storm evolutions are selected based on their maximum wind speed. With this model, sensitivity analyses are performed to determine the importance of certain model choices and time variables for the flooding probability of dikes and dunes. The relevance of each parameter is determined in order to define the amount of stochastic parameters. Therefore a probabilistic model, based on numerical integration and an optimization algorithm (from OpenTURNS), is developed to evaluate different failure mechanisms using the hydraulic loads from KustProfy, in a full-probabilistic and time-dependent manner. The failure mechanisms considered in this study are the erosion of the grass revetments of the outer and inner slope, backward erosion piping and dune erosion.