The Formation and Fate of a River Plume: A Numerical Model

Abstract

A mathematical model that describes the formation and dilution of a frontally bounded river plume is presented. Such features were first studied at the mouth of the Connecticut River during periods of high discharge and have subsequently been reported elsewhere. The model incorporates the effects of nonlinear advection, Coriolis acceleration, time dependency, mixing, friction, and a free frontal boundary. A numerical solution technique is employed to obtain approximate solutions to several problems which are interpreted to yield new insights to the dynamics of these phenomena. In particular, computed solutions for the growth of a plume discharged from a radial source into a steady crossflow are presented for a variety of crossflow velocities and physical scales. These demonstrate that the stability of the layer to vertical shear in the horizontal velocity is sensitive to the relative directions of the crossflow current and that of a free Kelvin wave. The effect of a reversing crossflow, representative of a tidal current, is therefore of interest and calculations indicate that dyer plumes, like that of the Connecticut River, are diluted by vertical mixing soon after the times of high and low water. This conclusion is of obvious ecological importance.