Water release policy effects on the shortage characteristics for the Shihmen Reservoir system during droughts

Drought-induced shortages are inevitable because of unexpected abnormal dry weather and the increasing need for water resources. Therefore, assessment of possible shortage conditions for a specific water supply system is an essential component in water resources planning and management. In this study, the shortage characteristics for the Shihmen Reservoir in Taiwan are investigated. A description of the reservoir yield in terms of the shortage frequency, magnitude, and duration is developed first. The derived reservoir yield description under a given operating policy and demand includes the reliability, total shortage rate, frequency, single period shortage, event shortage duration and magnitude, and interarrival time of shortage events. Hedging is a common measure adopted in reservoir operation that involves accepting a small current deficit to reduce future severe shortages. The reservoir supply index is then developed to trigger hedging in this study. The shortage characteristics for different lead-time hedging rules show that the derived reservoir supply index is a useful indicator for triggering hedging and the differences among reservoir performance for various release policies are easily compared using the derived reservoir yield description in terms of probabilistic shortage characteristics.