Economic Assessment and Comparison of Gravity and Pressurized Water Distribution Network in Sistan

Water distribution method based on the type of water conduits can be divided into two groups, namely, open and closed systems, while on the basis of the energy of the water flow, the two groups are gravity flow and pressurized flow. Open channel type conveyance and distribution is achieved by gravity and includes channels made by embankment construction, excavation, or construction of prefabricated sections, as well as the use of underground pipes or closed ducts in which water flows by gravity (no pumping).  If the required pressure for the flow of water is less than 10 meters, the conveyance and distribution method is grouped as low-pressure. In this research, the irrigation and drainage network of Sistan, which is a strategic region in east parts of Iran facing severe water shortage, was studied to suggest proper strategies. Three crops, namely, wheat, barley, and alfalfa were studied for economic analysis. The results showed that using a piped conveyance system would increase the net income and the gross benefits of the wheat and alfalfa growing farmers compared to open channel systems, but the area of barley should decrease. Furthermore, due to high costs of construction and low irrigation efficiency and poor water management, the net benefits of farmers under the two conveyance systems would not be significantly different. Thus, by using pressurized water conveyance systems from Chah-Nimeh reservoirs, the existing efficiency of 20%, would rise to 90%. Results revealed that the main problems in the network were deterioration of canals lining, poor performance of the regulating and distribution structures, and low efficiency of the network. Overall, the economic analysis of the project showed that water conveyance by pipe was economically more justified than open channels.