Determining the hydrological characteristics of the Greater Zap River basin by gis

Water resources management is closely linked to the concept of river basin characteristics. Basin is a dynamic and very complex system which has mainly two types of characteristics; geographic and hydrologic. In this study, the hydrologic characteristics of the Greater Zab River Basin were determined by employing Geographic Information System (GIS). GIS techniques are useful not only in obtaining data from a basin; they also provide valuable contribution in performing the spatial distribution of hydrological data in assessment of water resources projects. The Greater Zab River is approximately 460 km long, flowing through Turkey and Iraq with a total catchment area of about 26,325 square kilometres (km2). The headwater of the Greater Zab River originates in the mountainous area near Lake Van, Turkey, where it springs at an altitude of 4,168 m above sea level and joins the Tigris River in the south western of the city of Hewler (Erbil), Iraq. The terrain pre-processing models, namely, fill sinks, flow direction, flow accumulation, stream networks, watershed boundary have been acquired from digital elevation model (DEM) by using spatial analysis tools in ArcGIS. Hydrological processing such as, map of sub-catchments, characteristics of sub-catchments, river network map and river network characteristics have been determined by employing ArcHydro tools. On the other hand hydrological analysis such as, slope map, Thiessen polygon map, Thiessen polygon areas were defined by Arc Toolbox. The annual average discharge of the stream flow at five flow measurement stations (FMS) along the river and the annual total precipitations measured at twenty-four rainfall measurement stations in the basin were used here in order to perform the hydrological analysis of the basin. The annual average discharge values were obtained from monthly average discharge measurements while the annual total precipitations were acquired from monthly total precipitations. Based on the stream flow measurements, rainfall-runoff coefficients were estimated by rational method for five sub-basins. The rainfall-runoff coefficient for the whole basin was found to be 0.53. Keywords: Greater Zab, Basin Characteristics, GIS, ArcHydro, Rational Method