Brine discharges from desalination plants into low-flushing water bodies are challenging from the point of view of dilution, because of the possibility of background buildup effects that decrease the overall achievable dilution. To illustrate the background buildup effect, this paper uses the Arabian (Persian) Gulf, a shallow, reverse tidal estuary with only one outlet available for exchange flow. While desalination does not significantly affect the long-term average Gulf-wide salinity, due to the mitigating effect of the Indian Ocean Surface Water inflow, its resulting elevated salinities, as well as elevated concentrations of possible contaminants (such as heavy metals and organophosphates), can affect marine environments on a local and regional scale. To analyze the potential effect of background salinity buildup on dilutions achievable from discharge locations in the northern Gulf, a 3-dimensional hydrodynamic model (Delft3D) was used to simulate brine discharges from a single hypothetical source location along the Kuwaiti shoreline, about 900 km from the Strait of Hormuz. Using nested grids with a horizontal resolution, comparable to a local tidal excursion (250 m), far field dilutions of about 28 were computed for this discharge location. With this far field dilution, to achieve a total dilution of 20, the near field dilution (achievable using a submerged diffuser) would need to be increased to approximately 70. Conversely, the background build-up means that a near field dilution of 20 yields a total dilution of only about 12.

A three-dimensional integrated hydrodynamic and water quality model of the Arabian Gulf has been developed in this study based on the hydrodynamic modeling program Delft3D. The model was forced by seasonal estimated discharges from all major rivers, validated tidal constituents, time-and depth-varying offshore boundary conditions, measured meteorological data and time-and space-varying wind and atmospheric pressure. The model performs well, especially when comparing results with measured coastal data in Kuwait, situated at the northwestern part of the Arabian Gulf. Simulation results suggests strong short-term dynamics and long-term seasonal variation of hydrodynamic and water quality processes of the Arabian Gulf including its northwestern part. It was pointed out from the results that the northwestern part of the Arabian Gulf has a strong dependency on river discharges and meteorology. Although only preliminary water quality modeling has been done in this study, results indicated relevant general characteristics of some water quality parameters and its great dependencies on forcing data.

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