Simulation and changes in the flood number and zoning of the Sistan River flood during different return periods with the HEC_RAS Model

In this study, gradually varying flows, bridges, culverts, and the slope of a one-dimensional river flow in a cross section on the Iran-Afghanistan border were investigated and evaluated in terms of the soil type in the riverbed and banks with two Manning coefficients, considering all parameters in two models with different normal depths, and performing simulations upstream, the water height in the main routes and the left and right plains of the river, the average width of the floodplain, its maximum and minimum values in different floods. It was determined that the reduction in flow strength causes sedimentation, increases the level of the riverbed, affects the hydraulic characteristics of the flow, and reduces the share of water intake from the Hirmand River. Therefore, the solution of increasing the slope And the width of the river upstream and downstream of the Kahak Dam is a suitable and feasible solution and increases water intake. The conditions for increasing the width of the Kahak Dam and the number of its gates and the stratification upstream of the Kahak Dam show that the share of river intake during times of water shortage (flow rates less than ۱۰۰ cubic meters per second) is insignificant and is less than ۱ percent (۰.۰۶ percent for a flow rate of ۵۰ cubic meters per second and ۰.۰۵ percent for a flow rate of ۱۰۰ cubic meters per second), and the amount of Sistan intake during times of water shortage for flow rates of ۵۰ and ۱۰۰ cubic meters per second is ۱۹.۶۳ and ۳۸.۳۲ cubic meters per second, respectively, and the ratio of models of mode ۱ and ۲ has an increase of approximately ۶۵۰ times.

Keywords:

Sistan River , Hydraulic Model , Kahak Diversion Dam , Water Intake Capacity