Non-stationary flood frequency analysis for Danjiangkou Reservoir in operation period
Danjiangkou Reservoir is the key hydraulic project for flood control in Han River basin,and the water source for the Middle Route of South-to-North Water Transfers Project.The design flood of Danjiangkou Reservoir is an important reference for reservoir operation and comprehensive utilization benefits,which was overestimated due to the short-recorded data series and the uncertainty of historical flood information in construction period.Besides,many reservoirs and water transfer projects have been built and put into operation in the upper Hanjaing River basin,which significantly altered the spatiotemporal distribution of streamflow.The Mann-Kendall test indicated a decrease trend for the annual maximum flood series from 1929 to 2023 with the statistical parameters all smaller than 0,which meant that the gauged flood data series was non-stationary.Thus,how to quantitatively estimate design flood of Danjiangkou in operation period has become an urgent scientific and technological challenge.The generalized additive models for location,scale and shape(GAMLSS)model was widely applied in non-stationary flood frequency analysis,which was based on the principle of time-varying moment method and assumed that the location,scale,and shape parameters of probability density function would follow certain mathematical relationship with corresponding covariates.GAMLSS-based time-varying P-Ⅲ distribution method was applied for non-stationary flood frequency analysis for Danjiangkou Reservoir in operation period.The selection of covariates would significantly determine the effectiveness of time-varying model.The reservoir index(IR)was defined with the hydrological characteristics and reservoir storage capacity,which presented superiority in design flood investigation.Meanwhile,diversion index(ID)was first proposed to quantify the influence of water transfer projects with mathematical definition inspired by IR.The IR and ID were selected as covariates to construct the time-varying P-Ⅲ distribution model,and the maximum likelihood estimation method was used to estimate parameters for the single covariate(IR)and the double covariates(IR&ID).Based on the annual maximum flood data series with 441-year historical investigation period(from1583 to 2023),the design flood for Danjiangkou Reservoir in operation period was estimated and compared with original design values.The main conclusions were summarized as follows:(1)The IR and ID were selected as covariates which could conform to the hydrological variation laws objectively.The fitting results of time-varying P-Ⅲ distribution with both covariates could reflect the flood series decreasing trend caused by upstream hydraulic structures.However,there was no significant difference for the time-varying P-Ⅲ distribution fitted with double covariates(IR&ID)or single covariate(IR).The influence mainly attributed to upstream reservoirs rather than water transfer projects,since the ID only slightly reduced about 2％design floods in Danjiangkou Reservoir.(2)The estimated 1000-year design flood of Danjiangkou in operation period has been significantly reduced.The flood peak and 7-day flood volumes were 45,000 m3/s and 12.3 billion m3,which were both reduced about 31％compared with the original designed values in construction period.The original designed flood of Danjiangkou Reservoir was overestimated which results in more discarding water and lower refill rate in flood season.Since the estimated design flood of reservoir in operation period has significantly reduced,the reservoir operation water level could be risen with the condition of flood prevention standard unchanged,which could not only generate more hydropower,but also increase the water resource utilization rate as well as reservoir refill rate.
design floodnon-stationary seriesflood frequency analysisreservoir in operation periodwater resources projectDanjiangkou Reservoir
万方数据
维普
