Many deterministic numerical models accurately predict wave action and coastal flow but are unable to represent sedimentary processes over geologic times either because their basic equations and numerical implementation do not allow the sediment-water interface to change through time, or because their degree of detail makes geologic-time simulation prohibitive. The model presented here builds upon knowledge gained in geologic modeling. It does not attempt to represent detailed fluid flow (such as individual waves). It handles only the properties of the flow that directly affect sediment transport at scales of spatial variability greater than about 100 m. The model exploits the fact that the unsteady component of the flow (waves, tides) is predominantly cyclic, and the flow's net effect on sediment transport can be characterized by a field of directional sediment transport rates. Daily and seasonal weather variations that modulate the flow can be incorporated statistically, allowing the transport field to represent a time period of several years. Each of the model's time steps can thus encompass many years, allowing an entire run to span time periods of geologic interest. In each step, the sediment transport field is calculated from water flow (waves and currents) and bathymetry. Then it is used to redistribute sediment and recalculate flow. The model incorporates long-term eustatic, climatic, and sediment-input changes by varying conditions between steps.