Riprap stability on the inner slopes of medium-height breakwaters

Abstract

Medium height breakwaters are subjected to a considerable amount of overtopping. This implies the armour on the inner slope has to stable against overtopping waves. Existing equations do lack some basic understanding of the process of starting up movement of rock on the inner slopes. In case one relates the stability of the blocks on the inner slope directly to the waves approaching the breakwater, the model should include not only the wave parameters (e.g. wave height, period, spectral shape, etc.) but also a number of the parameters of the construction, like the roughness, the breakwater height, the permeability, the outer and the inner slope, and many more. When performing such tests, it is not possible to separate the effect of all individual parameters on the stability, unless a very huge number of tests are carried out. Therefore, the idea is to separate the problem into two parts: • the incoming wave gives an amount of overtopping over and infiltration into the breakwater • the overtopping and the outflow cause an instability of the blocks on the inner slope.