Optimum Operation of MainOutfall Drain Syphon in Dhi Qar Governorate in Water Scarcity Conditions

Abstract

Descaling and cleaning of hydraulic structures are significant, which will affect on the rate of  increase discharge through them.Descaling is expensive and difficult unless it depends on the operating system to avoid or reduce the occurrence of deposits.The pumping system (pumping station and syphon) located at the intersection between the Euphrates River and Main Outfall Drain in Dhi Qar Governorate suffers from the accumulation of deposits due to untreated water and its source is the outlets of sewage stations at  u/s of a pumping station, in addition to the problem of shell growth in Headbasin (u/s syphon), where the shells move after sticking with a clay to the syphon area. Also, the low discharges in Main Outfall Drain trough during the dry seasons and due to climatic changes which was  prevent  pumping system with a design capacity,this affects on the possibility of occurrence the deposits due to the low velocity of flow. In this study, a hydraulic model was developed to increase the flow velocity to the maximum permissible using HEC-RAS 5.03 software by operating the pumping system in four scenarios under water scarcity conditions from (19-80) m³/sec for several days with closing the syphon gates. Alternating,this is increasing the flow velocity through the siphon body which helps prevent or reduce deposits  in syphon body. The simulation results proved as following: Closing two syphon gates and operating the third with one or two pumps running with a discharge of 19-40 m³/sec produced a velocity of 1-2 m/sec or closing one gate and operating the others while operating three or four pumps with a discharge of 45-80 m³/sec, a velocity of discharge inside the siphon was 1.12-1.5 m/sec.