Comparative Review of Longitudinal Dispersion Coefficient Equations in Rivers

Abstract

This paper presents analysis and estimation of the longitudinal dispersion coefficient, a key hydrologic parameter for transport of contaminants in rivers and streams. The longitudinal dispersion coefficient varies spatially in streams with changes in the hydrologic parameters, e.g., the cross-sectional width, depth, sinuosity, and velocity of flow. Many theoretical and empirical equations are reported in the literature. After a comprehensive review, 30 equations for prediction of the longitudinal dispersion coefficient were selected from published research. These equations were used in this analysis. Hydrologic data from 59 river reaches were used for estimation of the dispersion coefficient. The estimated values of the dispersion coefficient were compared statistically and graphically with the observed values. Results showed that sinuosity significantly impacts estimation of the dispersion coefficient. Computations that include sinuosity improve the performance of the dispersion equation. Observed and estimated values were compared, and the equations were ranked based on the accuracy of estimation. The nine top-ranked equations were used for field validation using the ICWater model. The Sahay equation provides the best results when used in the calculation of concentration in the advection dispersion equation.