A new method for calculating the downstream ecological flow of diversion-type small hydropower stations

Abstract Diversion-type hydropower stations play an important role in energy and power generation. However, they also substantially alter the natural hydrological situation of the river section through the formation of dewatered river sections between water-retaining structures and the power plant, which have a series of associated effects on the habitats of living organisms, thereby affecting the health of the water ecosystem. Therefore, it is of practical importance to study and analyse the ecological flow of the dewatered river section. Maintaining a certain ecological flow is considered to be an effective solution, but at the same time it can also affect the socio-economic benefits of hydropower plant operation. To reconcile the relationship between the two, this paper proposes a new method for calculating ecological flow in dewatered river sections, an optimal method for the phased habitat demand (OMPHD) of key species, in which key species are selected and explored in stages, giving priority to the key elements of each stage. Organisms have different life stages and these stages require a series of different habitats; habitats with a high geomorphological diversity have the best habitat suitability. In this study, basic data were obtained through inductive sorting, data collection, and a field survey of the Houxi River (a secondary tributary of the Yangtze River) and the endemic fish Schizothorax prenanti was selected as a key species. The hydrodynamic and fish effective habitats were calculated and simulated using relevant hydraulic formulae; a geomorphological diversity index (GDI) was introduced, and the target fish habitat area and geomorphological units, such as water depth and flow velocity, were analysed comprehensively to determine the ecological flow in the downstream dehydrated river section of the diverted small hydropower station. Flows of 17.5 m3/s and 5 m3/s were established during the spawning and non-spawning periods, respectively. This information provides a basis for the ecological restoration of river sections.