How Significant is the Wave Run-Up Reduction due to Underlayer Permeability in the Design of Rubble-Mound Breakwaters?

The present paper is concerned with an experimental investigation designed to quantify the influence of the permeability of underlayers (filter and core) on the wave run-up over rubble-mound slopes. The run-up measurements were carried out in a laboratory wave channel over a practically useful range of the surf similarity parameter over different structure configurations representing a range of the notional permeability factor (P). The results appear to suggest that the run-up reduction due to underlayer permeability is little, 2% and 5%, respectively, for values of P=0.1 and 0.4; however, the run-up reduction for structures with P = 0.5 and 0.6 is not insignificant, viz., 10% and 15%, respectively.