Wave reflection by submerged vertical and semicircular breakwaters

This short manuscript presents a laboratory investigation on the effects of submerged vertical and semicircular breakwaters on local wave characteristics, particularly with the aim of determining the parameterizations for the wave reflection coefficients for submerged vertical and semicircular breakwaters. Experiments were conducted with normally incident monochromatic waves breaking at the breakwater on both sloping and horizontal sandy bottoms. The reflection coefficient (Cr) is observed to rely mainly on the dimensionless submergence parameter, a/Hi (a—the breakwater's depth of submergence and Hi—the height of the incident wave at the breakwater). Two semi-empirical parameterizations are proposed to predict reflection coefficients for submerged vertical and semicircular breakwaters. While both parameterizations share the same functional dependency on a/Hi, the functions have different constant coefficients. For the limiting case when a approaches zero (breakwater crest is at the mean water level), the Cr value tends toward 0.53 for both breakwaters. However, as a increases, the submerged vertical breakwaters reflect more energy than submerged semicircular breakwaters for the same a/Hi value. Results of this study are expected to be of use to coastal engineers for preliminary feasibility and desk design of submerged vertical and semicircular breakwaters.