| The prevention of flash flood is the focus of flood control and disaster reduction in China,and rainfall threshold is the key to the success of flash flood warning and prediction.At present,the rainfall threshold of flash flood is mainly determined by hydro-hydraulic method and there are many factors involved.Therefore,taking the classical trial algorithm as an example,based on the establishment of HEC-HMS model in the study area,the sensitivity of the factors involved in the calculation of rainfall threshold was analyzed.The uncertainty of the rain pattern,the most important and key factor,was studied.The main research contents and results are as follows:(1)Establishment of HEC-HMS model and calculation and rationality analysis of traditional rainfall threshold.Taking Caohe in Xinxian County of Henan Province as an example,the HEC-HMS model of typical small watershed was established.Based on this model,the rainfall threshold of Caohe was calculated by trial algorithm,and the rationality of the rainfall threshold was analyzed by using the rainstorm data causing disaster.The analysis results show using the theoretical values of the rainfall threshold to warn and forecast flash flood will result in "false forecast".(2)Analysis of influencing factors of rainfall threshold.Morris screening method was used to analyze the sensitivity of Rainfall threshold Calculation parameters,and the rainfall peak location coefficient r and rainfall peak ratio b were selected as the characteristic parameters of rainfall pattern.The disturbance experiment design was carried out to analyze the influence of rainfall pattern on rainfall threshold,and the factors involved were comprehensively compared and analyzed.The results show that the characteristic parameters of rainfall pattern have the greatest influence on the rainfall threshold,and the influence of rainfall peak ratio b is greater than that of the rainfall peak location coefficient r.The parameters in relationship between water level and discharge also have great influence on rainfall threshold.In addition,the relationship between water level and discharge of Caohe Formation was rechecked.(3)Study on combination of risk probability(A,B)rain pattern in small watershed.In this paper,the risk probability of rainfall pattern was defined.By using Copula theory,a two-dimensional joint distribution function of characteristic parameters of rainfall pattern(total rainfall and intensity of rainfall peak)was constructed,and a method that can determine the combination of risk probability(A,B)rainfall pattern which can reflect the characteristics of rainstorm in small watershed and estimate the risk probability was proposed.The inferred rain patterns were compared and analyzed by using the rainstorm data causing disaster.The results show that the combination of risk probability rain pattern proposed in this paper is reasonable.(4)calculation of rainfall threshold with different combination of risk probability and establishment of O-G-P risk preference warning model.Based on the deduction of combination of risk probability rain pattern in small watershed,the rainfall threshold of Caohe was calculated by trial algorithm.The space of rainfall threshold was determined according to the current flood control capacity of Caohe,and the O-G-P risk preference warning model of flash flood was constructed,which provides a new way of flash flood warning and forecasting of small watershed in hilly area. |
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