Random wave overtopping of vertical seawalls on coral reefs

Abstract

Reliable estimations of overtopping rates are necessary for the design of vertical seawalls. Although many studies have been carried out to address this, few have paid attention to vertical seawalls built on coral reefs. In this study, a physical model was constructed with an idealized coral reef topography and vertical seawalls located on the middle or inner reef flat. A steep fore-reef slope in combination with a shallow and horizontal reef flat led to significant changes in wave heights, periods, spectra, and shapes across the reef. State-of-the-art overtopping formulas were tested against the experimental data, but none of them produced satisfying results. The reasons for the inapplicability of these formulas in this regard were discussed, which highlighted the necessity of distinguishing the significant influence of coral reefs on incident waves reaching engineered structures from structures fronted by relatively deep water and foreshores. A new formula for estimation of overtopping rates of vertical seawalls on coral reefs under non-impulsive conditions was derived. This formula is a function of the relative wave height at the seawall toe and the relative crest freeboard, whereas the spectral period is not incorporated. The performance of the new formula was investigated using various combinations of dimensional and dimensionless parameters.