Based on the law of mass conservation, a general three-dimensional diffusion equation of suspended sediment due to waves and currents, adaptable to estuarial and coastal areas, is derived by decomposing the instantaneous velocities and concentrations into three-different-time-scale components respectively. A three-dimensional suspended sediment diffusion equation adaptable to actual calculations is available as the result of the parameterizations of turbulent diffusion term and wave diffusion term. Different from the former diffusion equations, the influence of waves and currents on suspended sediment diffusion can be simultaneously reflected in the newly derived equation.
