Maintaining ecological flow and mitigating impacts on river health are among the core requirements for sustainable hydropower development. Designing specific operational modes to fit specific ecological conditions of rivers remains a key practical challenge for hydropower operation, especially in terms of balancing the various tradeoffs among multiple objectives in the context of coordinated operation of cascade hydropower plants.

For the model in this paper, the authors proposed a revised variable monthly flow method (RVMF) for the ecological flow determination; the variable incorporates variations of hydrological conditions, and also combines the classification concept of the Tennant method. For these objectives, they consider cascade power generation, the assurance rate of cascade power generation, and the assurance rate of ecological flow.

The preliminary application in the Yalong River case showed that (1) with the increase in environmental flow requirements of the river, the cascade power generation has dropped significantly, and the most affected is the Jinping-II hydropower plant; (2) there are clear tradeoffs between the cascade power generation and the assurance rate of cascade power generation, and the cascade power generation and the assurance rate of cascade power generation under different riparian ecological conditions; and (3) being able to quantify those tradeoffs provides crucial scientific evidence for stakeholder dialogue and informed decision making for hydropower operation modes that can achieve the best desirable balances between power generation and river health conservation.