Siltation and sedimentation problem in Mosul reservoir dam

Sammanfattning: Iraq depends on the Rivers Tigris and Euphrates for its water resources. Recently the flow of these rivers decreased drastically. In view of this situation the true storage capacity of the dams are to be evaluated to ensure prudent water resources management strategies. In this research, the biggest hydraulic structure in Iraq, Mosul Dam Reservoir, was studied to evaluate its present storage capacity.Mosul dam reservoir is located on the River Tigris in the north of Iraq, 60 km north-west Mosul city. The dam is a multipurpose project for irrigation, flood control and hydropower generation. The storage capacity of its reservoir is 11.11×109 m3 and water surface area is 380 km2 at the maximum operation level 330 m.a.s.l. The dam was operated on July 24th, 1986 and no survey had been conducted to determine its storage capacity since that time. A pre-construction topographic map for the studied area scale 1: 50000 dated 1983 was converted to a triangular irregular network (TIN) format using “Arc/GIS software version 9.3”. The TIN was used to establish the stage-area and stage-storage capacity curves before dam construction. The resultant curves were compared with the adopted operational curves. The results of this comparison showed that the percentage difference was 4.0% and 7.7% for stage-storage capacity and stage-water surface area curves respectively.Mosul reservoir was surveyed to find out the reduction in its storage capacity and to develop new operational curves. The survey was performed over 12 days from May 15th to June 3rd, 2011 using to “Echo sounder sonar viewer type Sea Charter 480DF” linked to a “Real-Time Kinematic Global Positioning System (RTK-GPS)”. The bathymetric survey results indicated that the reduction in the storage capacity of the reservoir due to sediment deposition during the operating period was 1.143×109 m3. This represents 14.73% of the total storage capacity and the reduction in the live storage and dead storage was 11.8% and 19.62% respectively. Likewise, the survey suggested new operational curves for Mosul dam reservoir. The survey showed that most of the sedimentation was in the upper zone of the reservoir and gradually decreased towards the dam.