Rubble‐Mound Breakwaters With S‐Shape Design

When a single‐slope, rubble‐mound breakwater is subjected to waves that dislocate the stones but do not cause any overtopping, the damaged section may become stabilized at a certain level of wave attack, generating the “S‐shaped equilibrium profile.” A further increase in wave height finally causes a complete damage of the breakwater. If an equilibrium profile of a rubble‐mound breakwater section is examined, it is observed that the resulting profile is similar to a three‐slope berm‐type section. The fact that an equilibrium profile of a rubble‐mound breakwater is reached under the attack of waves greater than the design wave brings the consideration of constructing the rubble‐mound breakwaters to equilibrium profiles initially, which may lead to the use of smaller armor units. To study this problem, a series of tests on a single, sloped (1:2) rubble‐mound breakwater section, constructed at a constant water depth, are carried out with regular waves in the laboratory. Under the same test conditions, i.e., same wave height, period range, water depth, and same armor stone size, the three‐slope berm‐type section produces up to 90% less damage relative to the 1:2 single‐slope section. Volumetric comparison shows that three‐slope berm‐type sections have less or comparable volumes to the 1:2 single‐slope section, due to reduced wave run‐up.