Spatial distribution of wave overtopping

Abstract

The goal of this master thesis is to describe the spatial distribution of the wave overtopping discharge over and behind the crest of a coastal defence structure. The influence of the most relevant parameters on this process is explored. This research has been performed by means of a physical model. The following relevant parameters were varied during the experiments to consider their influence on the spatial distribution of the wave overtopping discharge: wave height, wave steepness, water depth, crest height and wave spectrum. Four different types of wave overtopping discharges were measured in this research: total wave overtopping discharge, wave overtopping discharge directly behind the crest, wave overtopping discharge over impermeable backfill and wave overtopping discharge over permeable backfill. Based on the equality of the comparison between the experiment results and existing theoretical methods to calculate the total wave overtopping; further experiment results are considered as acceptable and reliable and can be used to derive the relation for the spatial distribution of the wave overtopping discharge. The total overtopping discharge flows over the crest of the breakwater and is divided in two components: the infiltrated discharge into the crest and the overtopping discharge directly behind the crest. A method to describe this distribution is defined. This method includes the influence of the wave height, wave length and crest height. The spatial distribution of the wave overtopping discharge behind the crest depends on the permeability of the backfill. For an impermeable backfill with a slope of 3% towards the breakwater, the overtopping discharge at every point behind the breakwater is divided in two parts: one part flows back over the impermeable backfill under the influence of gravity and the other part passes the point and travels further away from the breakwater. The final relation between the reduction factor (ratio between the overtopping discharge at a certain distance behind the crest and the overtopping discharge directly behind the crest) and the distance behind the crest was found to depend on a dimensionless presentation of the wave energy flux. For a permeable backfill, the overtopping discharge at every point behind the breakwater is divided in two parts: one part infiltrates into the backfill and the other part passes the point and travels further away from the breakwater. The influence of the wave energy flux on the relation between the reduction factor and the distance behind the crest was found to be smaller than for an impermeable backfill.