Hydrogeologic and Water Balance of Koi Sanjaq Basin, Northern Iraq

Hydrogeological investigation and water budget calculation of Koi Sanjaq basin is carried out. This investigation includes the determination of the aquifer types extending through the study area and flow direction as well as aquifer hydraulic properties values. Three main unconfined aquifer types were distinguished , they are (Pilaspi), , (Bihassan-Muqdadiya and Fatha –Injana) Formations , where the flow map of the unconfined aquifers shows that the flow direction is from northern and northeastern parts towards the south and southeastern parts i.e. .Lesser Zab River. Analysis of pumping test data of 9 selected wells from unconfined aquifers show that T values range from 1.51m^2/day to 64.4 m^2/day revealing the great variations in the aquifer lithology, extend of fissures and fractures as well as the saturated thickness of the water bearing zones. Water balance calculations are achieved using meteorological data of three meteorological stations: Erbil, Koysanjaq and Dukan , where Mehtas model is used to calculate the water surplus values which found to be equal 203.9 mm/ year. Soil Conservation Service method (SCS) and curve number methods are adopted to determine the amount of runoff where the soil type is the most critical factor. According to the infiltration rates measured by the authors, all of the study area soil is of A group, therefore the calculated value of runoff is 128.72mm/year. Overall calculations of the water balance components shows that the groundwater recharge is 75.18 mm/year, representing 10.84 % of the total rainfall for the study area.