CS(AR)-18/96-97 : Development of operation policy for Tawa Dam

Abstract

Reservoirs are one of the most important elements of water resource systems. They are used for spatial and temporal redistribution of water in accordance with requirement. Reservoir storage is necessary to use the highly variable water resources of a river basin for beneficial purposes such as municipal and industrial water supply, irrigation, hydroelectric power generation, and navigation. Under uncertain streamfiows and multiobjective demands, water allocation process becomes more complex. The evaluation of current operating rules of existing reservoirs is very important to meet the changing demands according to the public needs and objectives. An operating plan or release is a set of rules for determining the quantity of water to be stored or released from a reservoir or a system of several reservoirs under various conditions. The operating rules provide guidance to the water managers who make the actual release decisions.

Simulation models are used to represent a system and to predict the behaviour of the system under given set of conditions. Simulation models are limited to predicting system performance for a user specified set of variable values. On the other hand, an optimization procedure may involve iterative executions of a simulation model, with the iterations being automated to various degrees.

In this report, rule curves based policy has been adopted for the conservation regulation of Tawa dam. Rule curves are developed for three levels such as upper rule level, middle rule level (critical for irrigation), lower rule level (critical for water supply and upstream use). The generalised simulation model developed by the Water Resources System Group at N.I.H. is used to simulate the system operation and to refine the rule curves. A number of simulation runs have been taken by adjusting the rule curves and the final rule levels have been arrived to satisfy the target demands to the maximum extent possible. The current operating policy of the reservoir is also simulated and the results are compared with the recommended rule curves based policy.