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Karkheh basin is located in the semiarid and arid regions of Western Iran, an area with severe water scarcity. 70% of rainfall is directly evaporated. The potential annual evaporation of the southern and northern regions is 3,600 mm 1,800 mm, respectively. Agriculture plays an important role in the economy of the basin. In the present situation, 3.9 bm3 of water are used for irrigating 378,164 ha of irrigated agriculture (horticulture and field crops), and surface water and groundwater resources provide 63 percent and 37 percent, respectively, of this volume. Of the irrigated area, 76.5% is under cereals (wheat and barely), 23% under pulses, and 0.5% under cultivation of forage, orchards, melons and vegetables, and oil seeds. The area is particularly low in terms of yields, productivity and incomes. Irrigation efficiency in the basin is 28-36 percent and the overall Crop Water Productivity in the basin is about 0.55 kg/m3. In this paper, the specifications of the Karkheh Reservoir Dam & Hydroelectric Power Plant as the biggest dam in history of Iran with total volume of reservoir 7.3 Bm(3) and Karkheh irrigation and drainage network project are illustrated. Also the situation of water availability in the basin, surface and groundwater potential and some aspects of water resources management in the basin are considered.