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Determination of Optimum Effluent Discharge in Tidal Rivers to Prevent Seawater Intrusion

Authors:
[ Ghafouri ] - Department of civil engineering, Chamran university of Ahvaz
[ Jahanfar ] - MS of civil engineering

Abstract:

Many studies have been conducted about estuaries and tidal rivers in the past. It is mainly due to the importance of these very useful environments, which are main resources of freshwater in many coastal regions. Our objective in this study is the management of freshwater resources to control the water quality in tidal river water deteriorated by tide phenomena. It requires that the salt concentration be kept at a desired level in estuary while minimum freshwater is released from the upstream dam reservoir. It is noteworthy that one of the methods for preventing salt intrusion from sea to estuary is to control the rate of freshwater effluent discharge into tidal rivers. If the freshwater inflow increases, the salinity becomes less and set back faster. On the other hand, the freshwater resources are invaluable but not unlimited, it is necessary to manage the usage of this kind of resources correctly. Therefore an optimization problem arises. The optimization criterion of effluent discharge is to minimize the difference of river water concentration with that of desired concentration level. To achieve this, the hydrodynamic equations including one dimensional continuity and momentum equations along with salt transport equation for fully-mixed estuary solved by finite element method where a single effluent discharge resource is considered. It works as a tide simulation model in the estuary. Then a constrained optimization method, i.e. Augmented Lagrange Method (ALM) is applied. The objective function is also summation of square the difference between calculated concentrations obtained by simulation model, and desired concentrations.

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