Changes in Bed Morphology of Mosul Dam Reservoir

Abstract

Mosul dam is one of the biggest hydraulic structures in Iraq. It was constructed on the Tigris River in the north of Iraq for multiple purposes: irrigation, flood control and power generation. The initial storage capacity and water surface area of its reservoir reach 11.11 km3 and 380 km2 respectively at the maximum operation level 330 m.a.s.l. The dam was operated in 1986. Since that time no survey has been conducted to determining the characteristics of sedimentation in the reservoir. Blockage of the intakes of the pump station for North Al-Jazira Irrigation Project in Mosul dam reservoir has highlighted the importance of sedimentation problems within the reservoir.
Sediment distribution was studied within the reservoir. A comparison was made between the conditions at the start of the dam operation and a recent bathymetric survey conducted in 2011.The former was achieved using a topographic map scale 1: 50000 dated 1983 which was converted to a triangular irregular network (TIN) format using the Arc/GIS program. The results of the bathymetric survey were also converted to the TIN map format using the above program. Comparison of the two maps shows that the sedimentation magnitude in the upper zone of the reservoir, where the River Tigris enters, was highest and gradually reduced toward Mosul dam site. Maximum deposition thickness within the reservoir was 17.6 m. The thalweg bed slope of the River Tigris within reservoir area changed from 0.65 m.km-1 before dam construction to 0.71 m.km-1 on the 2011 survey. Zones within the middle and lower parts of the reservoir were exposed to erosion which amounted to 9.6 m deep.