This study shows the assessment methodology for the water resources of subsurface dams. The study area is SSangcheon subsurface dam. It is at the estuary of SSangcheon watershed forming the unconfined alluvial aquifer. there are several candidate area which are geologically similar to it at East coast. The groundwater level was computed by a 2-D FDM model, where the watershed discharge is the input as the infiltration term. The baseflow computed as the mean value of 3 watershed dischrge model is 0.5 m3/sec. And considering the inflow near the baseflow as the dry season inflow, The groundwater level according to the change of inflow and pumping rate was computed. Specifically, Using the real pumping rate 28000 m3/day which is equal to the supply amount of drinking water to Sokcho city, The inflow which induce the descended groundwater level to the bottom of aquifer or the ascended groundwater level that cause the surface flow was eatimated. The simulation for increased pumping rate and additional well construction to increase the water resources, was executed. And at the extreme dry season, available pumping rate was estimated.