A Risk-Based Reservoir Health Indicator for Long-Term Water Quality Assessment: Application to Dissolved Oxygen in Minab Dam

Dissolved oxygen (DO) fluctuations directly affect biological processes and water quality in a reservoir. It can occur gradually or rapidly as a result of a large input load of pollution. This paper proposes the Reservoir Health Indicator (RHI) as a weighted combination of reliability, resiliency, and vulnerability indices. The one-dimensional First-Order Reliability Method (FORM) and the empirical framework are applied to estimate these indices. The analysis uses 50 years of daily DO simulation results, acquired from molding a Minab dam divided into five non-overlapping 10-year periods. An indicator value greater than 0.5 reveals that the dam is healthy and sufficiently reliable in meeting the DO standard. Three weighting scenarios are applied to explore the RHI sensitivity. Results showed that in the first scenario, the approximate range of RHI variation is between 0.6 and 0.2. This indicates that after 20 years, the dam has lost its ability to improve its condition. In the second scenario, the variation is between 0.63 and 0.4, and the dam almost loses its health at 25 years. The third scenario indicates successful performance of the dam such that system has almost ability to recover itself by the end of its life. Therefore, developing such an indicator can effectively help understand the variation of a reservoir water quality by integrating three vital aspects of reliability, resiliency, and vulnerability.