Research On Reservoir Flood Control Risk In Karst Area Watershed Under Non-Stationary Conditions

Under the background of climate change and human activities,the hydrological cycle of our basin has changed,which affects the frequency,intensity and spatial and temporal distribution of flood events.Due to its complex underlying surface environment,karst watersheds are subject to variability under the influence of climate change and human activities,which poses a threat to water conservancy projects and downstream flood control safety.Based on this,this paper studies the problem of reservoir flood control risk in karst area basin under non-stationary conditions.The main contents and results are as follows:?1?The annual flood peak sequence,annual maximum 1-day flood volume sequence,annual maximum 3-day flood volume sequence and annual maximum 5-day flood volume sequence of chengbihe reservoir were used as the basic data,and the hydrological variation diagnosis method was adopted to make variation diagnosis of each flood sequence.The results showed that the annual flood peak sequence,annual maximum 1-day flood volume sequence and annual maximum 3-day flood volume sequence varied to different degrees,but the annual maximum 5-day flood volume sequence did not vary.The annual flood peak and the variation point of the annual maximum 3-day flood volume sequence were both 1979,and the variation point of the annual maximum 1-day flood volume sequence was 1980.?2?Based on the diagnosis results of variation points,the mixed distribution was selected to fit the empirical data of variation flood and calculate the flood design value,and the comparison was made with the existing design results.The results show that:?1?Compared with the traditional P-III distribution without considering the variation,the mixed distribution has better fitting to the empirical points,and the mixed distribution OLS and AIC values are smaller in the fitting test;?2?Under different design standards,and not considered Compared with the traditional P-III distributed flood design value of variation,the flood design value obtained by the mixed distribution is larger overall,and the higher the design standard,the larger the design value increases;?3?For the 10,000-year and 1000-year floods,the mixed distribution flood peak and the annual maximum 3-day flood design value are compared with the design values in the existing results,and the increase is about 8%and 4%respectively;?4?The existing design results in the 10000-year,1000-year flood peak design value The recurrence period under non-stationary conditions is 5400 years and 810 years,indicating that the existing flood design results have the risk of overestimating the flood and heavy current period.The non-stationary flood frequency analysis method proposed in this paper is adopted.Check the design flood.?3?The annual flood peak sequence of Chengbihe Reservoir and the maximum 3-day flood volume of the Chengbihe Reservoir are selected as the basic data.The mixed distribution of non-stationary flood sequences is used as the edge distribution.The Copula function method is used to construct the joint distribution of peaks and the two variables are analyzed.Based on the joint distribution design value and the condition frequency of the peak amount,the variable-variable ratio amplification method is used to derive the two-variable design flood process line.The results show that the design value of the two-variable joint distribution is larger than that of the non-uniform univariate distribution.For the 10,000-year and 1000-year floods,the design values of the annual flood peak of the combined distribution of the two variables increased by 1.83%and 2.52%,and the design values of the annual maximum 3-day flood volume increased by 1.64%and 1.97%.In terms of reservoir safety,the two-variable joint distribution design value is used as the standard value of flood control design,and the project is safer.Under the condition of non-uniform flood calculation,the two-variable design The flood process line is slightly higher than the univariate design flood process line,and the head-to-tail section does not change much,but the difference is greater at the flood peak.?4?Based on the two-variable return period as the flood control standard,considering the non-stationarity of flood peaks and floods,a non-stationary two-variable flood control risk model based on the joint return period was established to analyze the change of the reservoir dam risk rate under the limit water level adjustment.The results show that under the condition of non-stationary variation of flood,the flood water limit of Chengbihe Reservoir is raised from 185.0m to 185.2m,and the risk of flooding dam is unchanged;it does not exceed the risk standard of flooding dam 5.0×10^-6Under the conditions,the limit water level of the Chengbihe Reservoir can be raised to 185.6m,and the corresponding reservoir will increase the water storage capacity by 25 million m³.The comprehensive annual power generation and water supply of the reservoir will increase by about 2 million yuan.