Influence of the wave period in the dune erosion model DUROSTA

Abstract

The dune erosion prediction method presently used in the safety assessment of the Dutch dune coast was developed for situations with wave periods up to 12 seconds. New insights predict that situations with wave periods larger than 12 seconds can be expected. Preliminary analyses of the potential influence of larger wave periods on dune erosion indicate that more erosion occurs for a larger wave period. The objective of this study is to examine the performance of the process-based model DUROSTA model regarding the influence of the wave period, using large scale physical model tests. Results from the physical model tests and DUROSTA simulations are analysed for two wave periods, i.e. peak wave periods of 12 and 18 seconds. The performance of the different sub models in DUROSTA is examined in more detail, to obtain better insight in the physical processes within in the model. It is concluded that the wave propagation model functions well in the near dune area. DUROSTA underestimates undertow velocities and near dune sediment concentrations significantly. In both the large scale experiments and in the DUROSTA simulations a wave period effect presents itself mainly in higher sediment concentrations, rather than in higher undertow velocities. Morphodynamic computations are carried out to study the integral performance of DUROSTA. It is concluded that in general the profile development is well simulated for both wave periods. A clear wave period effect is observed in terms of erosion volumes. After 2.04 hours (5.0 hours in prototype) the relative increase in erosion volume is 25 percent in the physical model tests and 35 percent in DUROSTA computations. A detailed analysis of the results shows that slope effects and the method used for extrapolation of transport over the dry profile, have a large influence on predicting dune erosion with the DUROSTA model.