中文摘要：

设计洪峰流量的推求过程中,特大值判断的正确与否对洪水频率分析的精度有着较大的影响.而在特大值判断的过程中,Ex＋kσ常作为水文频率分析中特大值判断的准则,其中k为经验常数,其取值的不同常会给设计流量的计算带来较大的误差.采用数值模拟方法,生成符合PⅢ型曲线分布的样本,再通过适线拟合,探讨了k值与样本总量、变差系数及偏态系数之间的相互关系,并在此基础上建立了k值估计公式.最后,通过将该k值的估计公式应用于天然河道设计流量的推求过程中,取得了良好的效果.

英文摘要：

In the process of determining the design quantity of flow,the correctness of judging the extraordinary value has a significant influence on the accuracy of hydrologic frequency analysis.In the process of the hydrologic frequency analysis,the result of Ex＋kσ is often taken as a standard in judging the extraordinary value.As there is no unified rule,the value of k is usually determined as an experiential value which brings errors to the design quantity of flow.In this paper,based on the distribution of PⅢ curve,samples are created by a numerical simulation method to study the relationship between the k value and the samples′ amount,variation coefficient and skewness coefficient.A formula to calculate the value of k is also derived and performed well in the hydrologic frequency analysis of a natural river,which reveals the superiority of the improved method in this paper in judging the extraordinary value mentioned.