TABLE OF CONTENTS In this chapter, a predictive model for salt intrusion in well-mixed alluvial estuaries has been presented. In most cases the equation for steady state can be applied to the HWS situation, yielding a very simple equation to predict the intrusion length: Equation 5.72. This equation is physically based in that it relates to the main driving mechanisms for salt intrusion: the gravitation circulation (determined by the Estuarine Richardson Number), and the residual circulation (determined mainly by E/ a). Also in the unsteady state situation the method provides a useful tool, which is demonstrated by application in the Gambia and in hypersaline estuaries, such as the Saloum and the Casamance.
The strength of the method lies in its simplicity, while retaining its physical basis. The disadvantage of the method is that it requires a simplified topography. In cases where the topography is complex, one may have to rely on a two-dimensional model. But such models require large amounts of data. Even in case a more complex model is required, the one-dimensional model presented here can provide valuable information for the organization of a hydrometric survey: with the one-dimensional model, one can see which variables are most important and in which, density of observation.
