Evaluation of sediment management strategies for Tarbela reservoir

Abstract

Globally, multipurpose large dams play significant roles by providing water for irrigation, flood control and hydropower. This study aims to evaluate different strategies for the evacuation of deposited sediments in Tarbela reservoir by using Hydrologic Engineering Center-River Analysis System. Sediment flushing from existing power tunnels was found infeasible due to the downstream constraints and the loss of hydropower. New sediment bypass tunnels on the right-side bank of the dam to overcome the constraints were analysed. The sediment balance ratio, long-term capacity ratio and economic analysis were computed along with sediment modelling for different scenarios. The most technically viable scenario was 90 days flushing at 390 m drawdown level with a discharge of 5000 m3/s. This scenario was not economically feasible in terms of net present value, internal rate of return and the benefit cost ratio. The upstream under construction Diamer Basha dam was also evaluated. The results suggested a large volume of sediment would be trapped in the upstream reservoir, which would ultimately lead to a significant reduction in the inflow of sediment and the delta movement in the Tarbela reservoir. This option was recommended due to its multiple benefits and potential capacity to enhance Tarbela reservoir's life.