Dune erosion : product 2 : large-scale model tests and dune erosion prediction method

The dune erosion prediction method presently used to assess the safety level of dunes along the Dutch coast was developed for situations with wave periods up to Tp = 12 seconds, while situations can be expected with wave periods larger than Tp = 12 seconds. Preliminary analyses of the potential influence of longer wave periods on dune erosion indicate that larger wave periods lead to more dune erosion. However, effects of the wave period are not quantified sufficiently yet. To allow for the five yearly safety assessment of the Dutch primary water defences the current safety assessment method needs to be extended to take the effects of the wave period into account. The present report describes the second phase of this development. The objective of this phase of the study is to perform largescale physical model tests in the Delta flume of WL | Delft Hydraulics that provide data to validate the deterministic dune erosion prediction methods developed in the first phase of the study, and to select one of those methods for the use in the following phases of the study. Three largescale dune erosion tests were carried out with a depth scale of nd = 6. Based on the results of the tests it was found that the dune erosion volume above the still water level increases with 24 % for an increase in wave period from Tp = 12 s to Tp = 18 s (prototype) after a storm event of 5 hours (prototype). One of the deterministic dune erosion prediction methods developed in the first phase of the present dune erosion project was selected for the use in the following phases of the project. This method (Option wl2b) has the current method (DUROS) as a starting point. Therefore, it should be considered as an extension of the present set of equations.