Modeling Dispersion in Tidal Channels

Dispersion in unstratified tidal channels is analogous to dispersion in streams. In a southern California inter-tidal wetland characterized by depths of roughly 1 m, a dye study illustrates non-Gaussian longitudinal mixing characteristics which are predicted using a depth-integrated numerical model that uses physically meaningful mixing parameters. Longitudinal dispersion is based on Elder's model and transverse mixing is based on observations by Ward. Mixing parameters are linearly related to the product of shear velocity and the depth. Flow resistance and dispersion are scaled by a common parameter, the bed roughness. The numerical model, based on the finite volume method, gives non-oscillatory flow and transport predictions and is stable for Courant numbers less than one and diffusion numbers less than one-half. The finite volume method facilitates use of physically meaningful mixing parameters since these may be arbitrarily small and not affect model stability.