The development and application of a two-dimensional long-term dynamic numerical transport model which is capable of describing the spatial and temporal slowly-varying distributions of conservative constituents in shallow, well-mixed estuaries is presented. The model provides a basis for economically and practically analyzing the overall environmental effects of water resource development and estuarine management programs on the natural state of coastal waters. The concept of using net velocities determined over a tidal cycle for convective inputs to the transport model reduces the solution time for a particular problem, yet provides temporal resolution consistent with that necessary for long-term analyses. The solution method used in the model is an alternating direction implicit numerical scheme applied to central difference approximations of the derivatives in the basic two-dimensional convective-dispersion mass-balance equation. (Author)