Evaluation of Sediment Management Options and Minimum Operation Levels for Tarbela Reservoir, Pakistan

Dams are strategic assets as they provide water for irrigation, hydropower generation and control floods for rapid economic growth. However, due to lack of suitable sites as well as socio-environmental concerns, the development of new reservoirs has reduced, which necessitates better management of existing ones with consideration to sediment removal for storage conservation. This study presents an analysis of sediment management options available in the literature for Tarbela Reservoir. RESCON model has been used for technical and economical viability of flushing, dredging, trucking and hydrosuction processes. It is found that dredging and trucking are technically feasible but economically non-feasible, whereas, hydrosuction is technically non-feasible for Tarbela Reservoir. Reservoir flushing has been found technically and economically viable for this dam. HEC-RAS model has been used in the present study for carrying out Tarbela Reservoir sedimentation analysis to evaluate the options of: (i) sediment management through appropriate reservoir operation and (ii) constructing the proposed multipurpose Diamer Basha Dam, located at the upstream. The simulations lead to the conclusion that both the options are feasible. The reservoir storage depletion can be reduced and its life can be extended up to 27 years by lowering the minimum operation level from 457 to 401 m. The storage conservation may enhance the irrigation benefits and will reduce the devastations due to floods. Further studies are recommended to envisage the impact of high sediment outflows on turbines, tunnels and downstream reaches for Tarbela Reservoir operation at lower minimum operating levels and flushing.