A modeling study of the impact of increasing water exchange rate on water quality of a semi-enclosed bay

Abstract

As a result of decreasing water level of the Caspian Sea and excess pollutants flowing into Gorgan Bay, water quality of the bay has deteriorated significantly. This study aimed to propose effective engineering approaches which can improve the water quality of the bay. Special focus was placed on increasing the rate of water exchange between the water body and the Caspian Sea by either dredging existing inlets between the two water bodies or creating an artificial inlet on the Miankaleh Peninsula, which can help to dilute the polluted water and flush pollutants out of the bay. A coupled hydrodynamic and solute transport model was employed to investigate the effects of different measures using the concepts of residence time which is an important tool used to identify biogeochemical processes and their consequences in water bodies. Model results showed that the engineering approaches would have a profound effect on the water quality of Gorgan Bay by reducing the residence time. Opening an artificial inlet in the west of the Peninsula would reduce residence time by two times. Furthermore, in economic terms, these strategies would also improve the standard of living of most of the inhabitants who live around the bay. However, from an environmental perspective, the engineering approaches would threaten the ecosystem of the bay in various ways, such as disrupting physical, chemical and biological processes taking place in the bay. Finally, it was concluded that the most sustainable approach is to control the stressor – pollution coming from Gorgan Bay watershed and entering the bay. This study clearly shows that restoration projects require a multidisciplinary systems approach.