Development of an Algorithm for Contingency Planning in Dry Period

In order to minimize the impacts of drought and its consequences, Integrated Water Resources Management (IWRM) is needed in a region with multifaceted water dependencies. A prerequisite to IWRM is the sound management of water resources system components. Reservoirs play a major role in droughts impacts mitigation especially in arid and semi arid regions where there is too much difference between water supply and demand. Using hedging rules beside water allocation policies and traditional rule curves, reduces the magnitude of water shortages during droughts. Hedging rules curtail deliveries over some range of water supply to retain storage for use in the next dry periods and provide assurances for higher priority water uses. Hedging rules are used when reservoir has low refill potential or uncertain inflows. In the present paper, Ahar-chay basin in the northwest of Iran has been considered as the case study. Historical climatologic and hydrologic data in this basin shows that it has experienced a drought event during years 1998–2006. This drought has highly affected the available water resources of the basin. The Sattarkhan dam is the only available surface water resource in the study area. The optimization model that incorporates hedging rules and the classical rule curves is developed for modifying the water allocation in drought periods. The composite objective function of the models is to minimize the shortages of demand supply and maximize the water storage volume in the reservoir. The results of applying the proposed reservoir operating model are compared with the results of a deterministic model optimized by Genetic Algorithm (GA). The extent at which a storage facility meets the demands has been measured by performance indices and the efficiency of the hedging rule in modifying the normal operation policies. The results show that using the hedging rules can decrease the shortage magnitude and expected drought damages considerably.