中文摘要：

本文选取渭河华县站1951~2011年间年最大日流量以及年最大3日、5日和7日洪量资料作为研究对象,首先引入基于皮尔逊III型分布的时变矩模型分析了洪水序列的趋势性,然后以前期影响雨量和水土保持面积作为解释变量,建立洪水序列分布参数与解释变量的函数关系,结果发现洪水序列都存在明显下降的趋势并且与这两个解释变量是显著相关的。在Pettitt变点检验的基础上,以基于皮尔逊III型分布的时变矩模型推求四组洪水序列时变的概率分布,通过同频率放大得出变点前后两个时期10,50,100,500和1000年一遇的典型洪水过程线。结果发现,四组洪水序列均在1985年发生明显的突变,序列的均值在变点之后有显著的下降,由此造成相同重现期对应设计洪水的量级在变点之后大大减小,设计洪水过程线也明显坦化。

英文摘要：

Under changing environments, the flood series of the Weihe River have been influenced by climate change and human activities. In this paper, four flood series including the annual maxima daily discharge, 3-day flood volume, 5-day flood volume and 7-day flood volume of the Weihe River are chosen in the derivation of design flood hydrographs. The time-varying moments model based on Pearson type III distribution is applied to investigate the trends of the flood series, and then both the antecedent precipitation and the water-soil conservation land area are introduced as the explanatory variables of the distribution para- meters of the flood series. It is found that all the four flood series present obvious decreasing trends. Both the antecedent precipitation and the water-soil conservation land area are significant covariates of the flood series, and it is mainly the increase in the water-soil conservation land area that has led to the de- creasing trend of the flood series. Also by using the time-varying moments model based on Pearson type III distribution, frequency analysis is performed for each time period of flood series with the change-point identified by Pettitt method. The results indicate that all flood series have a downward change-point in 1985. Finally, the design flood hydrographs with the return periods of 10, 50, 100, 500 and 1000 years before and after the change-point are derived. As a result of nonstationarity, the volume of the design flood for a given return period after the change-point is far less than that before the change-point, and the design flood hydrograph also becomes much flatter.