Estimation of Monthly Oscillations of the Groundwater Exchange in Coastal Area

There is groundwater flow exchange between coastal aquifers and water bodies such as the sea, lake or gulf, in nature and this exchange can be of great importance with respect to the characteristics of the water body. The Bandar-e-Gaz coastal aquifer is located in the Gorgan Gulf region in northern Iran, and the Gorgan Gulf area has a very high ecological and environmental importance due to its specific conditions. In this study, the exchange of groundwater flow between the coastal aquifer of Bandar-e-Gaz and Gorgan gulf was simulated using the GMS mathematical model during the 24-month period. The results show that during the low flow periods, the sea water level and groundwater outflow from Bandar-e-Gaz aqufer to Gorgan gulf reach to its maximum (-26.37 m) and minimum (1331939 cubic meter per month) respectively, while in high flow periods there are reverse pattern. Moreover, consideration of time series of studied observed and estimated variables shows that the range of changes of groundwater outflow from the coastal aquifer is much higher than changes of sea water level. Based on the simulation results, it can be concluded that a hydraulic gradient under the influence of relatively limited changes of sea water level can have a completely significant effect on the change in groundwater outflow from Bandar-e-Gaz aqufer to Gorgan gulf.