Developing optimal operating reservoir rule-curves in drought periods

In this study a simulation-optimization model is developed for deriving operation rule-curves in drought ýperiods. To each reservoir, two rule-curves with adjustable monthly levels are introduced dividing the ýreservoir capacity into three zones between the normal water level and minimum operation level. To each ýzone of a reservoir and for each month of the year a hedging coefficient is introduced that determines the ýrelease from the reservoir. Accordingly, an optimization problem is developed in which the objective is ýthe minimization of water demands deficits in drought and the decision variables are the rule-curves ýlevels and hedging coefficients. For optimization of the problem, a genetic algorithm equipped with a ýself-adaptive constraint handling strategy is used. To evaluate the objective function and constraints ýviolations, the flexible and widely-used WEAP simulation model is exploited and coupled to the ýoptimization solver. The model is then applied to the Zohreh three-reservoir system in the southwest of ýIran and compared to the Standard Operation Policy (SOP). According to the sustainability indices for ýthe system operated in drought, the obtained operating rule-curves are found significantly superior to the ýSOP. As a result of applying the rule-curves, the modified shortage index (MSI) and vulnerability ýý(extent) of the system are respectively improved by 22% and 28% compared to the SOP. Consequently, ýthe developed policy application resulted in longer periods of deficit (but less severe) as shown by ýdecrease in reliability (5%) and resilience (40%) indices. ý