Comparative Effectiveness of Reservoir Operation Applying Hedging Rules Based on Available Water and Beginning Storage to Cope with Droughts

The discrete hedging rule which runs through several hedging phases can be an effective method for water supply operation from a reservoir during drought periods. This paper aims to derive two different hedging rule curves of a reservoir: one rule is based on available water that accompanies prediction of the current period inflow and the other rule is based on the beginning storage alone. The current period inflow was obtained by the ensemble streamflow prediction using historical precipitation data. A mixed integer programming algorithm was used to determine hedging rule curves for water supply operation of Hapcheon dam, the Republic of Korea for the period from 1990 to 2005 that included a drought period. Complying with the derived hedging rules, reservoir simulation runs for the period from 2006 to 2010 were performed. The derived hedging rule curves based on the beginning storage were placed higher than the curves based on available water and induced earlier rationing of water supply. The rule based on available water included the current period inflow and its simulation resulted in faster recovery to the normal phase of water supply when the drought ended. The simulation results applying the rule based on available water were 25% better in terms of the total water supply deficit and reliability; they, however, were 5% worse on the vulnerability. When predicted inflow is not reliable, the hedging rule based on the beginning storage might be worth in practical reservoir operation to avoid severer shortage resulted from the bad prediction of the inflow.