Enhancing water security through integrated decision-making and selective withdrawal for sustainable reservoir management.

Effective management of water quantity and quality in reservoir systems is vital for strengthening regional water security. Selective Withdrawal Systems (SWSs) contribute to this goal by allowing the precise extraction of water from specific layers in stratified reservoirs, where water quality and other properties differ across depths. Climate change and management policies further influence the hydrodynamics of SWSs, significantly impacting reservoir water quantity and quality. This study presents a multi-stage framework to identify optimal SWSs as solutions for the Wadi Dayqah reservoir in Oman, using both quantitative and qualitative approaches. The framework begins with optimizing SWS operations to ensure adequate water supply, improve the quality of released water, and enhance overall reservoir conditions. In the next phase, a robust decision-making (RDM) framework addresses uncertainties associated with climate change. This framework evaluates generated states of the world (SOWs) using sustainability indices by combining optimized responses with climate uncertainties. Additionally, a cellular automata (CA) model assesses three critical approaches in sustainable reservoir management: water deficit, undesirable water quality, and eutrophic conditions. The optimization results revealed that the proposed SWS strategies consistently outperformed the current operational state across all objectives. Notably, the lower gate (Gate 1) played a pivotal role in meeting agricultural and environmental water demands, significantly contributing to water withdrawals. Sustainability indices (SIs) for the SOWs in the RDM framework were computed based on stakeholder-defined thresholds. The SI values for the first, second, and third approaches were 0.898, 0.709, and 0.533, respectively, demonstrating the effectiveness of the optimized strategies in mitigating water deficits, improving water quality, and reducing eutrophic conditions.