The Melen Dam is under construction to support the water supply to the Istanbul Metropolitan area. Karstified limestone, which forms the major aquifer in the region, crops out at the left bank of the reservoir and extends to the adjacent basin, where it is drained by two main springs. An area of 20 ha that is covered by this limestone is planned to be lined by concrete mass cover. Another spring that discharges within this lining area will be plugged by the concrete mass. As a consequence of uplift pressure, piezometric pressure is expected to build up underneath the concrete lining. Prediction and relief of the uplift pressure are of utmost importance in optimizing the concrete lining. This was achieved by performing a numerical simulation of the uplift pressure of the pre-lining and post-lining conditions at the site. This required development of a representative hydrogeological conceptual model as the very first stage of this study. The conceptual model was then transferred to a numerical model through the software Seep/w of GeoStudio (2007 version). The optimal design of the concrete lining was developed after performing a number of numerical simulations on the calibrated model. The model suggested that the uplift pressure would be relieved to an acceptable level by construction of drains underneath the concrete slabs at certain locations.