Study On The Normalization Method Of Design Flood Calculation Under Nonstationarity

The design value of peak discharge is an indispensable prerequisite for the planning and design of water related projects,operation control and regional water resources development and utilization.The traditional flood frequency analysis methods are based on the assumption of consistency to calculate the design peak discharge.However,due to the change of climate environment and the impact of human activities,the measured peak discharge sample series is no longer stable,resulting in the design value of flood peak discharge calculated by the traditional method based on the assumption of consistency is no longer reliable.Therefore,it is necessary to carry out non consistency Research on design peak discharge calculation.The existing analysis methods of flood peak frequency under the condition of non-uniformity are not mature.The time-varying moment method is usually used to fit the time-varying probability distribution of non-stationary observation sample data,and then the non-uniform design value is obtained.Most of them solve the problem of non-uniform frequency analysis by statistical means from the mathematical point of view.In view of the current climate and environmental changes and the impact of human activities on the future,there is a lack of necessary understanding of the physical mechanism.It is impossible to accurately describe the inconsistent characteristics of hydrological series and predict the impact of human activities in the future stage only through statistical means.Therefore,its greater uncertainty is unavoidable Question.Therefore,from the perspective of normalization,this paper puts forward the theory and method of normalized frequency analysis for the calculation of non-uniform design flood peak discharge,which provides a new idea and way to solve the design flood calculation under the condition of non-uniformity.The main contents and results of this paper are as follows:(1)Theoretical analysis of normalization method for constructing consistent hydrological series and its applicable conditions.This paper analyzes the effectiveness of the normalization traceability reconstruction method" and basin regulation and storage equation.The results show that the normalization method is a special case of the "traceability reconstruction method",that is,the traceability reconstruction when the peak volume relationship index ?=1;when the peak volume relationship index ?=1,the consistent peak discharge sequence can be effectively constructed.The normalization method is suitable for non-uniform sample sequences with obvious trend and determined peak volume relationship.(2)Based on the theoretical basis that the normalization method can effectively construct the consistent sample sequence,the normalized frequency analysis method is constructed to deal with the calculation of non-uniform design peak discharge,that is,the consistent sample sequence is formed after normalization,the distribution line shape is determined by hypothesis test,the parameter estimation of distribution line type and the design value of normalized peak discharge are calculated,and then expressed by normalization Finally,the method is applied to the calculation of design peak discharge of mahuyu basin.(3)The existing methods are used to calculate the design value of inconsistent peak discharge.In the face of the impact of climate change and human violent activities,the flood event design value with the concept of hydrological risk or reliability is becoming more and more important for the planning and operation of water related projects.Four risk-based non-stationary hydrological frequency analysis methods are used to calculate the design peak discharge of mahuyu basin under the condition of non-uniformity,and bootstrap method is used to calculate the uncertainty of design value of inconsistent peak discharge.(4)The design peak discharge and uncertainty of mahuyu watershed under the condition of non-uniformity are derived by using the normalized frequency analysis method and the risk-based non-stationary hydrological frequency analysis method respectively.The effectiveness of the normalization method is verified by comparing the existing non-stationary hydrological frequency analysis method with the design value of the new hydrological manual.The results show that the design peak discharge calculated by the normalized frequency analysis method is the closest to the design value of the new hydrological manual,and the uncertainty is minimum.