Cascade hydropower plants operation considering comprehensive ecological water demands.

Highlights • Consider the ecological base flow, fish habitat flow and navigable flow. • Combine the three methods to calculate the comprehensive ecological water demand. • Establish three operation models considering comprehensive ecological water demand. • Quantitatively analyze the relationship between power generation and ecologic flow. • NSGA-II is employed to solve multi-objective problem. Abstract Hydropower plants operation may change river flow, thereby degrading the stability of river ecosystems. The primary purpose of this paper is to compute the comprehensive ecological water demand and establish ecological operation models to quantitatively analyze the interactions between power generation and degree of ecological flow satisfaction under different operation modes. The comprehensive ecological water demand takes the river base flow, ecological flow process and ecological water demands of fish habitat during the spawning period into account. The driest monthly streamflow under a 90% frequency method, range of variability approach and two-dimensional depth-averaged finite element model were adopted to obtain the ecological flow. In addition, to study the impacts of the ecological operation of hydropower plants on power generation, three optimal operation models including a maximum power generation model (Model-I), a minimum ecological change model (Model-II) and a multi-objective optimization operation model (Model-III), are established. In model-II, the average annual power generation of the cascade hydropower plants decreased by 10.61% compared with Model-I, and meanwhile the degree of ecological change reduced by 75.41%, which means, the reduction of power generation by 35.66 × 108 kWh could lead to a reduction of 11.4% on the degree of ecological degradation. Afterwards, the multi-objective problem of economic and ecological benefits in model-III was solved by the application of NSGA-II. Among them, scheme 3 is recommended for Model III, and its power generation and degree of ecological change are 311.69 × 108 kWh and 6.64%, respectively. In general, mutual restrictions and conflicts between power generation and ecological demand are inevitable, but they can be optimized through multi-objective ecological operation models to fetch the coordinated development of economy and ecology. [ABSTRACT FROM AUTHOR]