Fluctuations in temperature and precipitation amounts due to climate change influence recharge rate of groundwater. Any variations in the amount of precipitation recharge and artificial discharge directly affect groundwater level and so the salt water intrusion rate in the aquifers, which are in contact with sea water. The purpose of this study is to determine the overall historical precipitation recharge trend in Sel&ccedil / uk sub-basin and to detect whether there is a decrease or increase in recharge amounts due to climate change since 1100 BC. Besides, it covers assessing the future position of the salt water-fresh groundwater interface as a result of possible fluctuations in climate and artificial discharge. For this purpose, numerical density dependent cross sectional groundwater flow with solute transport model was conducted using finite element approach. At first, current salt water-fresh water interface and artificial discharge related head changes in the aquifer were determined. Backward modeling was utilized to obtain concentration distribution in the year 1976 representing the last stage of the undisturbed period. Then, progradation of salt water-fresh water interface since 1100 BC to 1976 was modeled using calibrated parameters and current recharge value. As a result of sea-regression model simulations (1100 BC-1976) less degree of salt water intrusion than that of currently detected in the area was obtained. The result suggests that overall recharge amount in the last 3076 years must have been less than that of 1976. Moreover, future (2010-2099) position of the interface and head changes under the influence of both climate change and increasing water demand were determined. Future model simulations indicate that salt water-fresh water interface moves farther landward. However this movement is mostly due to increasing discharge amount rather than that of climatic changes.

Seawater-fresh groundwater natural equilibrium conditions in the aquifers of the Sel&ccedil / uk sub-basin may be disturbed by the discharge occurred during the past 30 years in order to supply water for irrigation and domestic purpose usage. Two dimensional density dependent cross sectional saturated flow and solute transport simulations were carried out to determine whether seawater intrusion has occurred in the Sel&ccedil / uk sub-basin due to the imposed discharge or the determined salt-water in the western section of the aquifers represents natural interface equilibrium conditions. The numerical simulation model was calibrated using field measurements. The results of the simulations suggest that the seawater intrusion has occurred in the study area since the pumping activity increased in the region. Five scenarios were simulated for future predictions: (1) Present recharge and discharge conditions are maintained, (2) Discharge increases at a rate of the municipality need as a result of increasing population, (3) Discharge decreases by 12% from the present value, (4) Discharge decreases by 25% from the present value, and (5) No discharge occurs or recharge amount equals to the present discharge amount condition supplied to the aquifer. These scenario results suggest that seawater intrusion in the Sel&ccedil / uk sub-basin would progress in the following years unless proper management measures are taken into consideration. KEYWORDS: seawater intrusion, density dependent groundwater flow, solute transport, contamination, Sel&ccedil / uk sub-basin.