Medium-term scheduling of cascade hydropower systems incorporating ecological constraints considering spawning demand of drift-spawning fishes

As globally recognized flexible and efficient green and clean energy, the development and utilization of hydropower have progressed over the past few decades. Although the scheduling of hydropower stations is relatively extensively studied, most of the existing models are economic benefit orientated, namely simply pursuing the maximization of the benefit or the energy generation, while ignoring the negative impact on the ecological environment of the downstream. In fact, the spawning scale of drift-spawning fishes during the reproductive period is highly susceptible to flow rising processes, i.e., water level increasing process. The scheduling of hydropower stations can lead to changes in river water flow patterns that may severely affect the spawning activity of drift-spawning fishes. To this end, this paper proposes a cascade hydropower scheduling model with ecological constraints that coordinates the water discharge to meet ecological requirements, while pursuing the maximization of power generation. The ecological constraints can compensate for the negative impacts on drift-spawning fishes during the spawning period. Besides, the nonlinear constraints representing the operational characteristics of hydropower stations and hydropower units are linearized, rendering a mixed-integer linear programming (MILP) based scheduling model to facilitate the solving process. The case study with an actual cascade hydropower system located in a river basin in United States show that the proposed ecological constraints can effectively enforce flow rising processes, while the cost of power generation reduction is very limited. In addition, the computational burden accompanied with incorporating ecological constraints are acceptable for medium-term scheduling of cascade hydropower systems.