How does a rubble-mound breakwater absorb wave energy?

A rubble-mound breakwater absorbs wave energy primarily through the physical characteristics of its outer armoring and the voids created between its components.

Unlike vertical structures that rely on wave reflection, rubble-mound designs utilize the interstices (the spaces between individual armor units or boulders) to dissipate the energy of incoming waves. When waves strike the breakwater, the water is forced into these gaps, which act as an absorbent medium, effectively breaking down the wave's force.1

The efficiency of this energy absorption is enhanced by the shape of the armor units. For example, specialized concrete units like the tetrapod are designed to knit together, creating a stable, interlocking matrix that maintains these energy-absorbing voids while resisting displacement by storm conditions. By absorbing or throwing back the energy of maximum sea waves, these structures protect harbors and anchorages from the destructive power of the sea.12