Flood Frequency Analysis Considering Uncertain-Ties Under Changing Environments

Flood frequency analysis is the core link for calculating design floods and the basis for the design,operation and management of hydraulic engineering.In the context of the dual effects of climate change and human activities,in order to obtain reliable flood frequency calculation results,we perform the flood frequency analysis considering different sources of uncertainties.Firstly,the inconsistency components of flood sequence under changing environment are identified and diagnosed,and then the inconsisten sequence is reconstructed.Finally,the reconstructed sequence is used to perform flood frequency analysis by considering different sources of uncertainties.Primary conclusions drawn from this study are shown as following three parts.(1)Change point decetion of flood sequence under changing environment.This paper mainly uses the hydrological variation diagnosis system including three steps:(?)preliminary diagnosis,(?)detailed diagnosis and(?)comprehensive diagnosis.Taking the annual maximum flood peak discharge of Shiquan Station and Ankang Station in the upper reaches of the Hanjiang River as an example,the results show that the annual maximum flood peak discharge of Shiquan Station is a stationary sequence,and the annual maximum flood peak discharge of Ankang Station has jumped and changed in 1987.(2)Flood sequence reconstruction under changing environments.According to the diagnosis result,a system was established to reconstruct the inconsistency flood sequence based on the idea of "Decomposing and Composing".Trend component in the flood sequence is identified and eliminated by wavelet analysis.Jump component in the flood sequence is identified and eliminated by the method of centralization.The hydrological model method is used to calculate the flood sequence with multiple components as deterministic components.The consistency test is carried out on the reconstructed sequence.Results show that the reconstructed sequence obeys the consistency assumption which demonstrates the reasonalility of the applied method in this paper.(3)Flood frequency calculation considering multiple uncertainties.This paper develops a flood frequency calculation method that comprehensively considers three kinds of uncertainties,including sample sampling,model selection and parameter estimation.Based on the probability density function of flood variables which considering model and parameter uncertainty,this method gives the probability density function considering the three kinds of uncertainties by using bootstrap technology.Taking the annual maximum flood peak discharge of Shiquan Station and the reconstructed sequence of Ankang Station as an example,the results show that as the design frequency decreases,the uncertainty of the design flood value increases;Under the same design frequency,this method can effectively reduce the interval width and dispersion of design estimates by considering the uncertainty of sample sampling,model and parameter estimation,and can provide more reliable estimation results.