Is multicomponent environmental flow management always better than the fixed minimum flows for a river ecosystem?

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AbstractEnvironmental flows (e‐flows) management is a basic task in reservoir operation. A simple approach for managing e‐flows is to maintain a fixed minimum flow, which releases at least a constant amount of water to sustain daily streamflow. Then e‐flows management becomes increasingly more sophisticated. Newer approaches include multicomponent e‐flow management, which provides different flows during different periods. This management approach produces a better flow regime than the fixed minimum flows because it more closely resembles the natural flow regime. However, in addition to e‐flow management strategies, flow regimes are also influenced by reservoir capacity, reservoir inflow, and water supply. The effects of these three variables on flow regime alteration have been rarely studied. To compare the effects of different reservoir capacities, reservoir inflows, and water supply quantities on flow regime alteration, we developed a hypothetical reservoir system for use in numerical experiments. In addition to the fixed minimum flows, we tested the effects of three other widely used e‐flow management strategies on flow regime alteration: the fraction of inflow, flow components, and four‐period release approaches. The range of variability approach is adopted to evaluate the flow regime alteration. The results show that the flow regime alteration decreases with increasing reservoir inflows and increases with increasing water supply quantity for all of the four e‐flow management strategies. We found that for certain values of reservoir capacity, reservoir inflow sequence, or water supply, the simple fixed minimum flows approach may produce the same results as the more sophisticated approaches.