Study on the theories and methods of ecological flow guarantee rate index under different time scales.

Human activities have altered the region's natural attributes to a certain extent, leading to the competition of resources. As a result of the contradiction between water use inside and outside the river, the river ecosystems are under increasing pressure. Ecological flow has been proposed to ensure the health of the river ecosystem and habitat integrity. However, there are few special studies on its guarantee rate and lack of systematic analysis. To scientifically evaluate the ecological flow guarantee rate, this study proposed an ecological flow guarantee index for long-time by frequency analysis and an ecological flow guarantee index for short-time by Satisfaction Rate. Taking four typical sections of the mainstream of the Huai River as the research objects, we evaluated the ecological flow guarantee rate at different time scales based on the runoff sequence from 1956 to 2018. It was found that over the mid-long term scale (multi-year series), the guarantee rate of each section during the non-flood period reached 87%, while the guarantee rate during the flood period was about 83%. Over a short time scale (day series within the year), taking typical years of wet, normal, dry, and withered years to calculate the guarantee rate within the year, the average ecological flow guarantee rate reached about 70%. In practice, the joint application of the mid-long term and short-term ecological flow guarantee rate can take into account both long-term planning and short-term regulation, ensuring the sustainable development of river ecosystems in all aspects.