Reliability design of breakwater armor blocks considering wave direction in computation of wave transformation

Abstract

Recently Hanzawa et al. developed a reliability design method for the calculation of the expected damage level of armor blocks of a horizontally composite breakwater. In their method, the wave transformation from deepwater to the design site was calculated by assuming unidirectional random waves being normally incident to a straight coast with parallel depth contours. In real situations, however, directional random waves with variable principal wave directions will be incident to the shore of irregular bathymetry. In the present study, the reliability design method of Hanzawa et al. was extended to take into account the variability in wave direction in the computation of wave transformation. The directional variability includes directional spreading of waves, obliquity of the design principal wave direction from the shore-normal direction, and its variation about the design value. Even though the wave incident angle to the breakwater could be calculated, normal incidence was assumed in the calculation of the damage level of armor blocks. It was found that the inclusion of directional variability in the computation of wave transformation had great influence on the computed expected damage level of armor blocks. The previous design, which disregarded wave directionality, could either overestimate or underestimate the expected damage level by a factor of two depending on water depth and seabed slope.