Three Dimensional Beach-Stage Model

A three dimensional beach model applicable to open sandy coastal environments is presented. The model consists of ten beach stages incorporating erosional and accretionary sequences of beach-surfzone morphody-namic conditions. Each stage is associated with a particular level of breaker wave power. Decreasing breaker wave power produces spatially controlled onshore bar migration, eventual bar welding, beach accretion and reflective surfzone conditions ($$beach stages 6 \rightarrow 5 \rightarrow 4 \rightarrow 3 \rightarrow 2 \rightarrow 1$$). Increasing wave power generates beach erosion, dynamically controlled bar-channel formation and dissipative surfzone conditions (stages $$1 \rightarrow 2 \rightarrow 3 \rightarrow 4 \rightarrow 5 \rightarrow 6$$). Temporal variations in wave power cause predictable movement through and within the model. The effect of beach gradient (tan $$tan \beta$$) is considered with regard to the influence on the degree of dissipativeness, edge wave length and cut-off modes, and standing wave length. Steeper coarse grained beaches are more reflective and tend to lower (1, 2, 2') reflective stages; fine sand, low gradient dissipative beaches favor outer and multiple bars reflecting higher stages (5, 5' and 6); with low to moderate gradient, medium sand beaches potentially encompassing the entire spectrum of beach stages presented in the model.