一、概述 根据观测的洪水资料所组成的样本,采用理论频率曲线外延推求指定重现期下的设计流量,是目前通用的基本方法之一。外推设计洪水可靠性的重要因素是理论频率曲线的线型是否合理和统计参数的估计是否适当。由于水文系列的总体是未知数,由资料的小样本来估算统计参数,其样本的误差是较大的,上述的不确定因素增加了外推时的复杂性。长期以来, I. Overview Based on the samples composed of the observed flood data, it is one of the basic methods to use the theoretical frequency curve to determine the design flow under the specified return period. An important factor in the extrapolation of the reliability of the design flood is whether the linearity of the theoretical frequency curve is reasonable and whether the statistical parameter estimate is appropriate. Since the overall hydrological series is unknown, statistical parameters are estimated from small samples of the data. The errors of the samples are large, and the above uncertainties increase the complexity of the extrapolation. For a long time,