مطالعه تأثیر رسوب زدایی سد سپید رود بر شبکه آبیاری سپید رود

Water requirements of paddy fields in the Gilan Province are provided for by a large irrigation network including Sepidrud reservoir dam, Tarik diversion dam, Fumanat network, Sangar diversion dam, and Sangar right and left canals. Because of the deposition of sediments in the Sepidrud reservoir, its capacity has been reduced profoundly. To overcome this problem, sediments are flushed in the second half of each year. The sediments coming from erodible surfaces of the Sepidrud watershed area out flowing from the dam in the spring, and the deposited sediments in the Sepidrud river in the second half of each year are a great hazard for the irrigation network. The objective of this research is to study the effect of the sediments on Sepidrud network. In this research, sediment data from the hydrometric station near Sepidrud dam were analyzed. Sediment samples were collected by a hand sampler (type DH-48) from Tarik and Sangar diversion dams, upper and lower ends of Sangar desilting basin, BP4 and SP3 canals, and field ditches and drains. Water discharge was measured by a current meter. Deposited materials in irrigation structures were sampled for grading. The results from this study indicate that the Sepidrud river and Tarik diversion dam deposit sediments at low discharges, but at high river discharges these sediments were found to he erodible. Average efficiencies of left and right desilting basins of Sangar diversion dam were 15.3% and 11.2%, respectively. The area located in Fumanat section, which receives water from Tarik diversion dam, requires desilting structures. The irrigation structures of the network are in danger of sediments. The main and the secondary canals, compared with 3rd and 4th order canals, have less settled sediments in them.