Abstract
A large number of reservoirs have been built in the Yangtze River basin in the last few decades, the operation of which inevitably impacts on natural runoff. It is important to quantify the impacts of a cascade reservoir group operation on the hydrological regime in the downstream Yangtze River. The indicators of hydrologic alteration (IHA), range of variability approach (RVA), and Dundee hydrological regime assessment (DHRA) methods, which are based on five essential characteristics, i.e., magnitude, time, frequency, retardation, and rates of change, have been widely used to quantitatively analyze variation in the hydrological regime before and after the dam construction. The observed flow series at Yichang and Datong hydrological stations, located in the middle and lower reaches of the Yangtze River, respectively, are divided into pre- and post-dam construction periods by the Mann-Kendall (MK) rank correlation method. The results of the MK test reveal that the annual minimum discharge at Yichang Station has significantly changed since 2000. The analysis results of the IHA, RVA, and DHAR methods show that the hydrologic regime changed moderately after 1999 and is close to severe change after 2008 at Yichang station; and changed slightly after 1999 (the post-dam construction period) and moderately after 2008 at Datong station. A new typical year assessment method that can avoid the requirement for a long data series was proposed and compared with the RVA and DHAR methods. The results indicate that the hydrologic regime severely changed at Yichang station and moderately changed at Datong in 2014, which is consistent with the results of the above methods. This study further demonstrates that the changes are mainly reflected in the factors related to low flow such as mean discharge from January to March, minimum discharge, frequency and duration of low pulse, and so on. It is expected that further hydrological alterations will occur as the number of large cascade reservoirs constructed and operated in the Yangtze River basin increases.
Highlights
Numerous reservoirs have been constructed for the purpose of flood control and meeting the increasing energy demand
The observed flow data in 2014 at Yichang and Datong stations can be selected as a typical year for the Indicators of Hydrologic Alteration (IHA) factor analysis
Twenty-four large reservoirs constructed in the Yangtze River basin were selected in this study
Summary
Numerous reservoirs have been constructed for the purpose of flood control and meeting the increasing energy demand. These reservoirs have impacted on the natural runoff [1] and the flow regime [2]. To understand the impact of these changes on the natural environment, many indicators were proposed to assess the hydrologic alterations. Maingi and Marsh [7] used the IHA method combined with statistical methods to compare the incoming flow of Tana River in Kenya before and after construction of reservoirs; their results showed that the construction of reservoirs increased the minimum discharge, reduced the peak discharge, and affected the hydrologic regime. Olden and Poff [4] used long-term flow records from 420 locations across the USA and found that the IHAs adequately represented the entire ordination space by using 171 hydrologic factors (including the seasonal patterning of flows; timing of extreme flows; frequency, predictability, and duration of floods, droughts, and intermittent flows; daily, seasonal, and annual flow variability; rates of change; and so on)
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