The Effect of Structural and Hydraulic Perturbation on Water Surface Profile in Irrigation Networks

Reduction of water resources and low efficiency of irrigation networks makes it necessary to pay attention to the management methods and the proper operation of the irrigation canals. In each irrigation network, there is a large number of offtake and cross-regulators that any change in their operating situation affects the behavior of other structures and lead to decrease in the hydraulic performance of canals. The structural perturbation is formed under partial changes in the setting of offtake and cross-regulator, which causes variations of the design depth and water surface profile. Partial changes in the inflow of a canal discharge lead to hydraulic perturbation and variation in water surface profile. In this research, in order to investigate the influence of structural and hydraulic perturbation on the flow depth, the governing Gradually Varied Flow (GVF) equation was linearized by Taylor's expansion and an analytical equation was developed to calculate the water depth changes. Then, for various hydraulic conditions, the results of the numerical solution of the governing GVF equation and the developed analytical formula were compared. The results showed that the errors of the presented formula to calculate the water surface profile changes under structural and hydraulic disturbances were less than 4% and 3.8%, respectively.