干、支流洪水作用下洪水组合样本的选择对防洪设计的影响

Influences of sample selection of synthetic floods from trunk stream and tributary on flood control design

不同的洪水组合样本反映的干、支流洪水变量相关性是不一样的,对防洪设计存在着一定的影响。以桂平航运枢纽水闸为例,运用Copula函数构建干流浔江年最大洪峰与支流郁江年最大洪峰、浔江年最大洪峰与相应时段郁江流量、郁江年最大洪峰与相应时段浔江流量3种洪水组合样本的联合分布,在此基础上随机模拟洪水组合经调洪计算推求防洪水位,对比这3种洪水组合样本对防洪设计的影响。研究表明:3种洪水组合样本联合分布拟合最佳的Copula函数均为Clayton Copula;浔江年最大洪峰与相应郁江洪峰流量组合样本得到的防洪水位更加合理,既不高估洪水风险也不会低估洪水风险,在经济性与安全性之间取得了较好地平衡,该组合样本推求的100a一遇防洪水位为43.54m,相比采用经验方法确定的原设计洪水位43.48m更安全。Copula-Monte Carlo法考虑了干、支流洪水间相关性以及洪水组合与调洪耦合的关系,设计结果更合理。

The correlation of variables of flood from trunk stream with those from a tributary varies with sample selection of synthetic floods,which has a certain impact on flood control design.In the case study of Guiping Shipping Hub,this paper applies Copula function to construct the joint distribution of three samples of synthetic floods,the annual flood peak of the trunk stream,Xunjiang,and that of the tributary,Yujiang,the annual flood peak of Xunjiang and the flow of Yujiang in the corresponding period,and the annual flood peak of Yujiang and the flow of Xunjiang in the corresponding period.Influences of three samples of synthetic floods on flood control design are evaluated by applying stochastic simulation of synthetic floods and derivation of flood control level through flood routing.The results show that the optimum Copula function fitted by the joint distribution of three samples of synthetic floods is Clayton Copula.The flood control level derived according to the synthetic flood of annual flood peak of Xunjiang and the flow of Yujiang in the corresponding period is more reasonable,neither overestimating nor underestimating flood risk,thus achieving a better balance between economy and safety.The derived flood control level for 100-year return period flood is 43.54 m,safer than the original design flood level determined by empirical method.By taking into account the correlation of flood from trunk stream with that from a tributary and the coupling relationship between synthetic flood and flood routing,the Copula-Monte Carlo method adopted in this paper is considered to be more applicable to the flood control design.