Research In The Effect Of Underlying Surfaces Variation On Uncertainties Of Parameters Estimation In Hydrologic Frequency And Risk Analysis Of Reservoir Flood Control

As climate change and the inf luence of human activity intensifies,watershed underlying surface con ditions change dras tically.So th e hydrological sequence consistency condition is destroyed,and the traditional hydrological frequency analysis methods are not suitable for the inconsis tency of hydrological sequence.Xidayang Reservoir with sign ificant change of the land surface condition in the con trol watershed was chosen as the study area.The variation form s of annual m aximum flood peak discharge sequence,the flood p eak sequence consistency correction,the uncertainty of frequency distribution curv e parameters estimation,and the extreme flood control risk rate were carried on stat istical analysis and calculation.The main research contents and results are as follows:(1)The change trend,change point and type of the variation of the annual maximum peak flow series of the reserv oir were detected using the hydrological variation diagnosis system.The peak fl ow series of different frequencies corresponding to the past and current land surf ace conditions were calculated by th e frequency analysis m ethod for inconsiste nt hydrological series to im prove the accuracy and reliability of hydrological statistical analysis.(2)The un certainties of pa rameters of T ype Pearson-? distribution(P-? distribution)were estima ted by Markov Chain Monte Carlo(MCMC)sim ulation method,and 95% confidence intervals of parameters were determ ined.The hydrological frequency analys is was calculated based on the coupling of estim ated parameter and curve fitting,then the estim ates ranges of flood peak flow of design frequency after and bef ore were determ ined.The indexes cove rage rate,average bandwidth and average bias degree were c hose to evaluate the optimal benign of estimates ranges.The r esults show that the revised coverage ra te has increased by 17.10%,and the revised averag e bandwidth and average bi as degree reduced by 15.77% and 3.27% separately.Thus,the reliability of predicted uncertain ranges was improved by consistency correction of in consistency of hydrol ogical sequences influenced by human activities.(3)The c eck flood level of Xidayang Rese rvoir was chosen as the extreme risk control index,and the extreme flood control risk rate was calculated by the frequency analysis method.The calculated results under the past and current land surface conditions were 0.00769%,and 0.00508%,resp ectively.It is obvious that the reviewed extreme flood control risk rate was lower than the check criterion of a 10000 years flood(0.01%).In addition,the result can provide technical guidance for the dynamic flood control level,the full utili zation of flood resource in the flood season and the improvement of comprehensive benefits of Xidayang reservoir.