Modeling the Yield–Evaporation–Spill in the Reservoir Storage Process: The Regulation Triangle Diagram

From the dimensionless reservoir water budget equation, a graphical method to model the yield–spill–evaporation loss trade‐off in the reservoir storage process was built. The reservoir inflows were transformed into three parts that sum to the total mean inflow for long‐term operation: evaporation, spill and yield. A regulation triangle diagram (RTD) has been proposed to provide a better understanding of the reservoir storage process as a function of reservoir capacity, hydrological river regime, evaporation and reservoir morphology. The inflows were assumed to be serially uncorrelated and to originate from a Gamma probability distribution function. The diagrams were developed using the Monte Carlo method, while the graphics were developed for intermittent rivers with a coefficient of variation of annual inflows that ranges from 0.6 to 1.6. In the model, the reservoir is a single over‐year system, and the values are referenced to the steady state conditions.