Refined operation of cascade reservoirs considering fish ecological demand

Reservoir ecological operation creates artificial hydrological and hydrodynamic conditions to meet the demand of fish during key life periods, which provides eco-environmental protection to alleviate the negative impact of hydropower development on ecosystems. However, based on practical ecological operation experience, the flow experiments were rough in terms of plan design, most of which were implemented over short time frames, and circumstances where downstream flow conditions existed were inconsistent with fish requirements during periods affected by different local reservoir operation conditions. This finding suggests that current ecological operations leave considerable space for strategy refinement. This study proposed a methodology for designing refined operation strategies incorporating more ecological demands into reservoir operation releases to create and improve suitable ecological conditions for the spawning of representative fish species. A joint water quantity operation model of cascade reservoirs and an under dam-river hydrodynamic model coupling the operation conditions of hydroelectric generators was built. The proposed methodology was applied to the Three Gorges Dam (TGD) and Gezhouba (GZB) Dam cascade reservoirs in China. The simulation results indicated that (1) in most cases, the target of continuous flow increase on an hourly scale could be simply accomplished via hourly joint water quantity operation of TGD-GZB cascade reservoirs. (2) Maintenance of the average Dajiang and Erjiang generator output during the spawning period of Chinese sturgeon at a high outflow of 15000 m3/s could more effectively expand the integrated suitable space of Chinese sturgeon. We aimed to provide suggestions and references suitable for cascade reservoirs in China and worldwide to develop and optimize ecological operation conditions in more refined and diverse ways.