A three-dimensional physical model study was conducted to investigate toe stability of coastal structures in a breaking wave and ebb flow environment. The model study was conducted at a midscale on the order of 1:25, model to prototype. The study included both fixed-bed and movable-bed experiments. The purpose of the fixed-bed experiments was to determine a method to calculate a stable toe stone weight subjected to breaking waves and ebb flow. It was necessary to conduct the experiments on a fixed bed to isolate the problem and eliminate the variable of scour. Movable-bed experiments were conducted to verify the results of the fixed-bed study. A method to determine toe stone size was developed based on fixed-bed experiments using varying values of wave height, wave period, ebb flow velocity, toe stone size, and water depth. The resulting recommendation is that, considering both wave and flow conditions, the toe stone weight required may be greater than one tenth the primary armor weight presently recommended for acceptable wave stability. The movable-bed experiments indicated that toe stone size selected using this method was stable for combined wave and current conditions. Results also indicated that toe protection should cover at least half the scour hole width. Movable-bed experiments conducted with bendway weirs indicated that these structures may be a suitable form of toe protection. However, development of specific design guidance would require additional research.
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