长江上游大型水库群对宜昌站水文情势影响分析

近年来,长江上游已建成一批大型水库,其运行调度必然会对下游的径流产生影响。水文变化指标法(IHA)和水文变化幅度法(RVA)是以水流的量、时间、频率、延时和变化率5种基本特征为基础,对建坝前后的河道水文情势变化进行定量分析的方法。根据长江流域大型水库群建设的实际情况,利用Mann-Kendall秩次相关检验法划分了宜昌站建库前后的流量序列,用来评估长江上游大型水库群对宜昌站水文情势的改变情况。M-K相关检验发现,宜昌站的年最小流量已经在2000年发生了显著性地变化;IHA和RVA分析成果表明,宜昌站的水文情势已经发生了中等程度的改变,主要是与小流量相关的一些因子,如1~3月平均流量、最小流量六个因子、低脉冲发生次数及持续时间等;随着以三峡水库为核心的上游大型水库群建成并投入运行,未来长江下游河道径流还将发生进一步的改变。

IMPACT OF UPPER YANGTZE RIVER LARGE-SCALE CASCADE RESERVOIRS ON FLOW REGIME AT YICHANG STATION

A large number of reservoirs have been built in the upper reach of the Yangtze River in recent years, whose operations would inevitably produce certain effects on natural runoff. The indicators of hydrologic alteration (IHA) method and range of variability approach (RVA), which were based on five essential characteristics, i.e. magnitude, time, frequency, retardation and rates of change, were both applicable to quantitatively analyze the variation of hydrologic regime before and after the dams beconstruction. Based on the larger reservoir group in the upper Yangtze River, the flow series were divided into pre- and post-dam construction by Mann-Kendall (MK) rank correlation method. Then the impact of the upper Yangtze River reservoir operations on hydrologic regime at Yichang station was assessed. The results of M-K test revealed that the annual minimum discharge has been significantly changed since 2000. The IHA and RVA results showed that the hydrologic regime at Yichang station has been moderately changed after the construction and operation of upper Yangtze River cascade reservoir system, in which the Three Gorges Reservoir plays a key role. This study further demonstrates that the changes are mainly reflected on the factors related with the low flow such as mean month discharge between January and March, minimum discharges, frequency and duration of low pulse and so on, and that more significant human-induced hydrological alterations are expected in the future in the Yangtze River.