An Empirical Approach for Determining Longitudinal Dispersion Coefficients in Rivers

Abstract

Determination of the longitudinal dispersion coefficient (LDC) of a river is needed in studies regarding cleaning the water and protecting its quality when nuclear, chemical or biological contaminants are discharged into the river. This study presents the development of an empirical equation for predicting the longitudinal dispersion coefficient in natural streams. Factors affecting the uniformity of the flow directly affect the LDC. Therefore, the hydraulic radius, defined as the ratio of the wetted area to the wetted perimeter, was considered as an important factor in determining the LDC. The presented equation relates the dispersion coefficient to hydraulic and geometric parameters of the flow, and was derived using dimensional and least squares analysis. The comparison of the predictions using 128 field data sets measured in 41 rivers in the USA has indicated that the proposed equation is reliable in predicting longitudinal dispersion coefficients in natural streams.