Due to decreasing precipitation in recent years, lack of perennial surface water resources, and the high volume of groundwater extraction in the vicinity of Tashk Lake (called Tavabe-e-Arsanjan), the groundwater level decreases, and as a result, salt water from Tashk Lake intrudes into the fresh groundwater coastal aquifers. Several technical countermeasures are used to prevent or retard the groundwater salinization process. One of them is to increase (artificial) recharge in upland areas to enlarge the outflow of fresh groundwater through the coastal aquifer, and thus, to reduce the length of the salt water wedge.
In this research, the natural recharge of groundwater is studied using the Cumulative Rainfall Departure (CRD) method with regards to the existing information in the study area. This study focuses on using both revised CRD (R-CRD) and CRD methods to simulate, and consequently predict, transient water table fluctuations. A user-friendly program named GREM, which is written in Visual Basic language, is used to minimize the difference between simulated and observed water table elevations. The simulated water table exhibits good agreement with the observed water table (modeling efficiency = 0.933). The percentage of the cumulative rainfall departure (r), which results in a recharge from precipitation, is estimated to be 33.6. This implies that less than half of the precipitation acts to recharge the water table. The results showed that the natural recharge is not enough to compensate the high volume of groundwater extraction in the study area. The end objective of this study is to provide the foundation for the construction of a regional model of the Tavabe-e-Arsanjan groundwater basin to enable sustained agricultural production while mitigating the impact of salt water intrusion.