The use of geographic information systems (GIS) allows for a very efficient analysis of spatial hydrologic data for water resources projects especially for water control studies. rn this respect, flood hydrographs for Mogan basin, Turkey for different durations and return periods are determined by using Soil Conservation Service (SCS) method. The basic parameter of the SCS method, curve number (CN), is evaluated by using GIS employing digital land use and hydrologic soil group data derived from analog maps. A Digital Elevation Model (DEM) of Mogan basin is constructed by making use of topographic maps with a scale of 1:25, 000. Flood hydrographs for these three productive subbasins of lake Mogan are attached and superimposed to obtain the total flood hydrographs. Total flood hydrographs entering into Lake Mogan are routed by Puls Method to determine the outflow hydrographs fi;om the lake; then, associated lake levels are computed. Furthermore, inundation maps of Lake Mogan are obtained; these results are presented by GIS techniques.