Estuarine Dispersion from Tidal Trapping: A New Analytical Framework

Abstract

Observations of tidal trapping in a channel connected to large volumes along its perimeter showed that the exchange between them is driven by advection due to tidal flows. Therefore, quantifying the longitudinal dispersion of scalars in the channel that results from tidal trapping was not possible using traditional frameworks, which assume that the exchange is a diffusive process. This study uses the concentration moment method to solve analytically for the dispersion coefficient of a solute in a tidal channel which exchanges advectively with volumes along its edges. This constitutes a new framework for analyzing the longitudinal dispersion that results from tidal trapping in systems such as a branching tidal channel or the breached salt ponds of San Francisco Bay. A comparison of dispersion coefficients from traditional, diffusion-driven frameworks for tidal trapping, the new advective framework derived in the present study, and observations show that the new formulation is best suited to this environment.