Abstarct: Nowadays, Geographic Information Systems (GIS) are widely used in hydrological studies. Topographic maps can be used for determination of basin characteristics such as stream network, storage volume of reservoirs and surface area of the storage volume. In this study, using topographic maps of Sarakhs basin, Digital Elevation Model (DEM) was generated. As one of the most important challenges facing the process of dam building is its optimal localization and the apt option selection criterion is its storage capacity that must be in proportion with the demanded water volume. In this study, the needed storage volume of Ardak Dam - situated in Khorasan Razavi, Iran- was estimated as the case study. Input and output data resulting in ripple curve helped to determine the demanded water volume. Then applying ArcGIS10.3 software, flow accumulation, flow direction, surface area of storage volume maps generated by DEM, elevation-volume and elevation- area graphics. Ardak dam reservoir storage capacity was estimated about 30 Mm3, and crest elevation and water surface area were estimated 46 meters and 1.66 Mm2 respectively. In the next stage, to evaluate the estimate accuracy, the estimated water surface area and storage capacity were compared with the reported ones by the Iran water resources management company. Finally, dam storage capacity was modeled for two other upstream cases, their storage capacity and surface area were calculated and compared with the current position of Ardak dam.