Research On The Determination Of Ecological Flow And Safeguard Measures In The Gansu Section Of The Main Stream Of The Yellow River Based On Hydrological Variation

Ecological flow is an important indicator to measure the intensity of water resources development and the health of ecosystems.Reasonable determination of ecological flow is conducive to promoting the protection of water ecological environment in the basin and realizing the sustainable utilization of water resources in the basin.In view of this,this study adopts cumulative anomaly method,piecewise linear fitting technology,iterative cumulative sum of squares algorithm,Morlet wavelet analysis and other methods to carry out hydrological variation identification from the aspects of mean,regression,variance and cycle;based on the improved Tennant method,the annual The distribution method,Q₉₀ method,NGPRP method and the comprehensive index ecological flow calculation method were used to determine the ecological flow,and an improved ME-Tennant evaluation model was constructed to evaluate the ecological flow.Taking a hydrological control section as an example,determine the suitable ecological flow of the watershed,and establish the ecological flow guarantee mechanism of the watershed.The main research conclusions are as follows:（1）Based on methods such as cumulative anomaly method,piecewise linear fitting technique,iterative cumulative sum of squares algorithm and Morlet wavelet analysis,the Xunhua,Xiaochuan,Identification of hydrological variation in measured runoff time series of hydrologically controlled sections in Lanzhou and Xiaheyan.The results show that:on the whole,the four hydrological sections have obvious mean value,regression and periodic variation,and no variance variation occurs.From the perspective of mean value,the mean variation points of the Xunhua control section are 1968 and 1986,and the mean variation points of the other three control sections are all in 1986;from the regression aspect,the regression variation identification results of the four control sections Basically coincident,the trend from 1956 to 1983 was close to stable,the trend of annual runoff series dropped sharply after 1983,and the trend from 1998 to 2017 rebounded;from the perspective of variance,there was no variance variation in the four control sections;from the perspective of cycle,The periodic variation points of the four control sections are all in 1986.（2）Determine the ecological flow based on the improved Tennant method,the annual distribution method,the Q₉₀ method,the NGPRP method and the comprehensive index ecological flow calculation method,and calculate and compare the ecological flow of the Gansu section of the Yellow River Basin under the hydrological variation conditions.The results show that the ecological flow results obtained by the five methods are all less than the average monthly runoff for many years,which can meet the minimum water volume required by the river to maintain the ecology and environment.The ecological flow values of the Xunhua,Xiaochuan,Lanzhou and Xiaheyan hydrological control sections in the flood season are larger than those in the non-flood season,which is in line with the characteristics of the Yellow River’s main stream with more precipitation in the flood season,and can better meet the flow required by the river ecosystem and maintain the river ecosystem health.（3）Based on the improved ME-Tennant evaluation model,the results of ecological flow calculation were evaluated,and the appropriate ecological flow was determined.The results show that the ecological flow determined by the comprehensive index ecological flow calculation method is the ecological flow of the Gansu section of the Yellow River Basin under suitable hydrological variation.Before hydrological variation,the annual average ecological flow values of hydrological control sections in Xunhua,Xiaochuan,Lanzhou and Xiahe were 122.0m³/s,159.4m³/s,200.4m³/s and 214.3m³/s,respectively,and the annual average ecological flows of each hydrological control section in the non-flood period were412.2m³/s,519.7m³/s,595.3m³/s and 608.4m³/s,respectively.After hydrological variation,the annual average ecological flow values of each hydrological control section during the flood season were 140.7m³/s,213.3m³/s,245.3m³/s and 233.1m³/s,respectively,and the annual average ecological flow of each hydrological control section during the non-flood period was323.9m³/s,448.0m³/s,554.9m³/s and 516.0m³/s,respectively.（4）Based on the analysis of the ecological flow guarantee rate of each hydrological control section,the ecological flow guarantee measures of the Gansu section of the Yellow River Basin were proposed.The results show that the ecological flow guarantee rate of the hydrological control sections in Xunhua,Xiaochuan,Lanzhou and Xiaheyan is very good before and after the hydrological variation.Overall,the ecological flow guarantee rate of the Xiaochuan,Lanzhou and Xiaheyan control sections in the sudden change period is better than the baseline Expect.Based on the analysis of the ecological flow guarantee rate,ecological flow guarantee measures are proposed from the aspects of ecological flow scheduling,monitoring,early warning and supervision,so as to promote the governance and protection of the ecological environment in the Yellow River Basin.