Inferring Breakwater Overtopping and Wave Transmission Per-formance Based on Armor Type

Abstract

The selection of the appropriate armor unit for use on a rubble mound breakwater is a cost decision related not only to the ability of the armor unit to resist wave attack, but also the resulting harbor agitation or structural damage associated with the wave transmission or overtopping event. In order to provide safe navigation and harbor tranquility, breakwater design must address the critical issues of overtopping and the resulting wave transmission it causes. The harbor designer's objective is to evaluate not just the relative cost of an individual armor unit placed on the breakwater, but to evaluate it as part of an optimized system considering the volumetric breakwater costs, the relative protection offered to the leeward side of the breakwater, and issues related to viewshed and aesthetic appearance. The evaluation and comparison of different breakwater armor types has historically been difficult to perform short of full-blown physical modeling. Studies and performance data to date have either measured the overtopping volumes and dis- charge rates that result from waves of various heights hitting a breakwater, or they have measured the transmitted wave climate in the basin when a wave of a particular height overtops a breakwater, but not both at the same time. Yet logically, for the same gross breakwater geometry, there should be a one-to-one correlation between the overtopping amount and the resulting trans- mitted wave. This paper outlines a simple mathematical methodology for computing overtopping volumes given transmission or vice versa. Using independently documented overtopping volumes and transmitted wave heights for rock armored trapezoidal breakwaters, a correlated relationship is explicitly developed between overtopping and transmission. This methodology allows for earlier selection of the most efficient armor type to use, given unit costs, variable breakwater volumes, and aesthetic goals.