THESEUS Deliverable ID2.5: Part D - Overtopping resistant and over-washed dikes

Within the THESEUS project, the present work task, WT 2.3, focus on the safety of coastal dikes and especially their strength resilience against wave overtopping. Overtopping is an important parameter for the design crest level of sea dikes and levees. The overtopping discharge is for a given structure geometry determined by the water level (freeboard) and the wave characteristics, and dike strength, have large variability.
Surface erosion caused by overtopping can lead to failure and is thus an important failure mode. The important action parameters to consider are the flow velocities and flow depths. Semi-empirical formulae have been developed by Schüttrumpf (2001) and van Gent (2002) for estimation of these overtopping parameters for long-crested and perpendicular wave attack. Formulae for the cumulative erosion on the landward slope, based on overtopping flow velocities, have been presented by van der Meer et al. (2010)
To account specifically for the effects of wave obliquity and short-crestdness, small scale experiments in a wave tank have been performed at Aalborg University. The objective has been to determine overtopping flow velocities and flow depths on the seaward slope as well as on the dike crest and the landward slope in oblique long-crested and short-crested waves. The study presented in the following is further described in the papers by Nørgaard et al. (2011) and Lykke Andersen et al. (2011).
Results from the present study will be integrated with additional numerical computations in WT 2.3, and used for the design of proper mitigation options at the THESEUS sites in WT 5.1 and 5.3.