水利工程对坝下径流的影响——以葛洲坝、三峡水利枢纽为例

水利工程建设在给人类带来抗旱防洪效益、发电效益、航运效益、养殖等效益的同时,也对河流水文动态产生了一系列的影响,主要表现为对径流的调节。基于宜昌站1890—2014年径流数据,综合采用径流集中度、集中期和相位差分析等多种方法,分析了水利工程建设对径流年内分配以及枯水期的影响。结果表明:宜昌站径流集中度呈现缓慢下降趋势并在2004年发生突变,2003年以后径流集中度相对于2003年以前下降0.06(下降幅度为12.98%),说明葛洲坝水利枢纽、三峡工程建成以后宜昌站径流在年内分配变得平缓,洪峰被有效削弱,且三峡工程对宜昌站径流集中度减少的贡献率大于葛洲坝水利枢纽(贡献率分别为92.03%和7.97%);葛洲坝和三峡水利枢纽建成后,宜昌站径流重心提前8d(集中期从8月9日提前至7月31日);宜昌站进入枯水期的时间提前约20d(三峡大坝建设以前,宜昌站在12月7—11日进入枯水期,建设以后在11月底进入枯水期),水利工程对水文过程的影响可能导致下游枯水期污染加剧和湿地生境提前缩小,进而影响下游水环境和湿地生物多样性。上述结果定量揭示了水利工程对水文过程的影响及其潜在生态效应,可为认识水利工程的生态影响以及流域生态环境变化的驱动因素提供科学依据。

Effects of dams on runoff in the lower reaches: A case study of the Gezhouba hydro-project and the Three Gorges project

The Yangtze basin is rich in water and biological resources, providing essential natural conditions for economic development in the southern region of China. Various water conservation facilities have been constructed in the basin to perform water resource scheduling and electrical energy conversion. By 2009, there were 46000 reservoirs built in the basin, with a total irrigation capacity of more than 120 billion m³. These projects were associated with benefits in terms of drought flood control, power generation, shipping, breeding, and so on, but also had both positive and negative effects on runoff. Therefore, watershed water security not only affects economic development and ecological security in the southern region of China, but also is an inevitable requirement for sustainable development. We participated in an academic conference on soil and water conservation and disaster prevention and mitigation in the Yangtze River economic belt, during which several scholars and experts extensively discussed the current problems in the Yangtze River basin. Some experts pointed out that the construction of the Three Gorges project and other water conservancies would lead to an advance in the timing of the dry season in the middle and lower reaches of the Yangtze River, resulting in increased water pollution, changes in the habitats of migratory birds, and a series of ecological problems. Although low water levels and floods are classified into the extreme hydrology category, early drought has no significant impact on human activity, and is not as well studied as floods. With the growth of the social economy and population explosion, the gap between the supply and demand of water resources is increasing. Especially in the dry season, several ecological problems are experienced, including increased water pollution caused by the reduction in runoff and river blanking caused by excessive use of low water resources. Thus, it is necessary to study the effects of water conservancy projects on the dry season. After the conference, we conducted a field visit and a survey along the Yangtze River area, with a view to use the data to effectively assess the impact of water conservancy construction during the dry season. Since the construction of the Three Gorges project has attracted greater attention, its water security and ecological benefits have always been the focus of discussions. Therefore, we selected Yichang station as the study area and analyzed the impacts of the Gezhouba hydro-project and the Three Gorges project on hydrological dynamics. Based on the runoff data of Yichang station from 1890 to 2014, the effects of water conservancy construction on the distribution of runoff and the dry season were analyzed using runoff concentration degree and period and phase difference analysis. The results showed that the runoff concentration of Yichang station tended to decrease, with a mutation occurrence in 2004. After 2003, the runoff concentration decreased by 0.06 (a decrease of 12.98%) from that before 2003. This indicated that after the completion of the Gezhouba water conservancy project and the Three Gorges project, the runoff distribution in Yichang station over the year became gentle and the peak floods were effectively weakened. The rate of contribution of the Three Gorges project toward decreasing the runoff concentration degree in Yichang station (92.03%) was greater than that of the Gezhouba water conservancy project (7.97%). After the Gezhouba and Three Gorges projects were completed, the runoff concentration period and beginning of the dry season in Yichang station have advanced (with advances of 8 and 20 days, respectively). Following completion of the water conservation projects, changes to the water-carrying capacity of the environment and wetlands in the lower reaches will take place earlier than previously, resulting in increased water pollution, changes in wetland biodiversity, and several ecological problems. Our results revealed the influence of the water conservation projects on hydrological processes and their potential ecological efficiency, providing a scientific basis to better understand the influence of water conservation projects on runoff.