Improving Sustainability in Reservoir Operations by Incorporating Future Shortage Risk and Past Hydrologic Drought Information

Abstract

This study was conducted to derive sustainable reservoir operating policies based on a sustainability index that integrates one reliability (RelV), one resilience (ResX), and two vulnerability (VulX and VulP) measures. The technique for order preference by similarity to an ideal solution (TOPSIS) is adopted to combine these four measures into an overall sustainability index, which is used as an objective function to search for optimal sustainable hedging policies. Three types of conditions, including demand-based rule curves, future water shortage probability, and past standardized streamflow index (SSI) information, are proposed to trigger hedging. The Nanhua Reservoir–Jiaxian Weir (southern Taiwan) is used as an example to explore the effects of the proposed optimization scenarios on the sustainability of reservoir operations. The results indicate that the proposed optimization scenarios outperform current operations by effectively increasing resiliency and reducing vulnerability but at the cost of a slight deterioration in reliability. Improvements in sustainability are attributed to the creation of more conditions that trigger hedging, which cope with storage variations, inflow seasonality, past drought conditions, and future inflow uncertainty. The best scenario, considering demand-based rule curves, zone-varying future water shortage probability thresholds, and past SSI values and trends, results in a sustainability index of 0.651 (rescaled RelV′=0.175, ResX′=0.519, VulX′=0.202, and VulP′=0.440), which exceeds the index 0.366 for current operations (rescaled RelV′=0.124, ResX′=0.995, VulX′=0.721, and VulP′=1.0) and 0.541–0.650 for other optimization scenarios (rescaled RelV′=0.181−0.315, ResX′=0.519−0.749, VulX′=0.205−0.415, and VulP′=0.300−0.440).