Hydraulic Response of Rubble Mound Breakwaters: scale effects - berm breakwaters

Rubble mound breakwaters have been extensively investigated in the last decades. Nevertheless, there still exists some white spots where only little knowledge and only poor design rules are available. Some of these white spots are due to new types of structures developed in recent years.

In this thesis is presented results from two experimental studies, in which the focus has been on overtopping of berm breakwaters and scale effects related to overtopping of conventional rubble mound breakwaters.

The berm breakwater is a fairly new type of structure considered in harbour protection. The present experimental test programme with berm breakwaters, has not only resulted in an enormous amount of overtopping data, but also establishment of a design formula to calculate average overtopping discharges. Further, the test programme led to an improved design rule for front side stability of berm breakwaters, which was not actually identifed as a white spot, but still there was room for big improvements. Rear slope stability and wave re ection has been discussed brie y.

The conventional rubble mound breakwater has been investigated for many decades. Anyhow, there is still room for improvements in some areas. One very important white spots is the uncertainty related to overtopping measured in a small scale model. There are some indications of rather large scale effects, which seems especially pronounced for low overtopping discharges, with unsafe results obtained in the model. This was investigated in the CLASH project, where comparisons of prototype and model data were performed. However, the problem was not completely solved in the CLASH project as many possible model effects were identiffed. In the present project small and large scale tests have been performed. These tests led to the conclusion that overtopping scale effects are most pronounced for structures with a low crown wall, where scale effect may go up to a factor of 20. For a crown wall higher than the armour crest, only small scale effects were identifed.