The paper considers estuarine processes from the deterministic viewpoint and emphasizes numerical solutions of differential equations via the digital computer. Briefly reviewed are some recent modeling efforts on two aspects of the simulation of estuarine processes. These are: the representation of currents, and water levels, and the representation of diffusion and the local change of concentration due to currents, diffusion, and source-sink terms. The source-sink terms represent waste loadings, bottom demands, growth-death rates, phytoplankton grazing, etc., and are considered more in the light of ecological modeling.