Narrow Results

The strengthening of existing dykes by using the previous structures as a basis created and will create a high variety of dyke profiles with complex geometries at the German North Sea coast. The determination of their effects on design wave run-up is still a problem both for future constructions and for checking up the design of already strengthened dykes with improved design procedures due to the state of the art. The development of mathematical models for wave run-up and overtopping on dykes allow detailed research on the effect of the variety of the geometry of dykes on wave run-up and overtopping. In order to check the reliability of these tools a research project has been started which is jointly carried out by six cooperating European institutions.

In the paper results of basic investigations on wave run-up in oblique waves performed in the wave basin of NRC-CHC (National Research Council - Canadian Hydraulic Centre) are presented.

In all tests a smooth 1 on 6 slope of the dike in constant water depth of 0.5 m was used. The wave height was constant H_m0 = 0.1 m, while using 4 different wave periods (T_P = 1.26 s; 1.46 s; 1.78 s; 2.53 s) for the generated TMA spectra. The angle of wave attack θ ranges from 0° to 40°. The directional spreading σ _θ was 0°, 10°, 20° and 30°.

The directional function was determined by non-linear regression of wave data measured at the toe of the dike and was calculated as γ_θ = 0.67 cos(θ) + 0.33 both for long crested and short crested waves. Considering refraction and shoaling on the dike up to the breaking area, the directional function proves to be of the cosine type γ _θ = 1.06 cos(θ) − 0.06 ≈ cos(θ) as well for long crested as for the short crested waves.

Wave overtopping was responsible for many dike failures in the past. It is not feasible to avoid wave overtopping completely in the future due to uncertainties in the prediction of the design water levels and the costs of uneconomical high dikes. Therefore, wave overtopping has to be taken into account for the design of seadikes. The overtopping flow velocities and related layer thicknesses are required which are responsible for infiltration and erosion of the dike crest and the landward side of a dike. The objective of this paper is to study the flow velocities and related layer thicknesses associated with wave run-up and wave overtopping based on theoretical and experimental investigations.