Identification of Scouring Zones in Ungauged River by Simulation: The Case of Galal Badrah River, Iraq

Abstract

Galal Badrah River is one of Iraqi-Iranian border crossing rivers. This river is usually seasonally flooded during any time started from January to May. Its maximum discharge is 2200 m3/s which was recorded during 1985. During floods, banks of this river at many locations need protection against scour problem during floods. A small dam was constructed on this river in 2010 for the purposes of flood control and storage of water.  The weir of the dam has a design discharge of 1250 m3/s. Sediments started to accumulate in the reservoir of the dam that reduce its design capacity to 10% during 2017. The flow of Galal Badrah River was simulated by using HEC-RAS 5.0.3 models. were used to simulate by using. Two hydrographs were used at upstream side of the river, one with a maximum discharge of 1250 m3/s and the other is of 2200 m3/s. A normal flow depth is used as a downstream boundary condition. Results of the simulation showed that the velocities to be higher than allowable velocity of scouring. The protection of Galal Badrah river by stack boulders is suggested to be used to avoid the scour at the river bank. The protection will increase Manning’s roughness coefficient from 0.028 to 0.10. The percentage of reduction in velocities after the river protection for the discharges of 1250 and 2200 m3/s were found to be 65.23% and 60.55%, respectively. The reduction in velocity caused increase in the river water levels. As a result, a flood embankment is required to be constructed on the right bank of the river with a height ranges from 2.5 to 5.6 m depending on the water depth at river cross section.