水文变异下洞庭湖四水环境流研究

探究水文变异前后环境流组成成分的变化特征,可为洞庭湖四水流域的生态保护与生态修复提供科学依据。基于湘、资、沅、澧四水(湘潭、桃江、桃源、石门)4个水文站1959-2016年逐日流量数据,运用Mann-Kendall法确定长时间序列径流的突变年份,并辅以累积距平和滑动T检验法校核检验,将时间径流序列划分为水文变异前后两个阶段,并以IHA软件为平台,分析四水流域在水文变异前后环境流的组成成分变化情况。结果表明,水文变异前后,四水流域各水文站环境流的组成发生了不同程度的改变;在湘潭站环境流组成中,小洪水极大值出现次数的偏移度最大,为77%,其环境流组成呈单一化趋势,整体流量过程逐渐并入到小洪水、高流量脉冲时间和枯水流量这3种事件中,流量事件发生的多样性减少;在桃江站环境流组成中,小洪水极大值出现时间偏移度最大,为150%;在桃源站环境流组成中,大洪水极大值出现次数偏移度最大,为150%;在石门站环境流组成中,特枯流量极小值出现次数偏移度最大,为252%;与水文变异前相比,桃江、桃源和石门站的环境流较为多样化,流量过程年内更加丰富。

Environmental Flows in Four Watersheds of Dongting Lake Under Different Hydrological Conditions

Xiangjiang, Zijiang, Yuanjiang and Lishui Rivers comprise a large part of the river system of Hunan Province and they all flow into Dongting Lake. In this study, variation in the environmental flows of these four Dongting Lake tributaries were compared before and after hydrological variation. Based on long-term daily runoff data (1959-2016) at hydrological stations (Xiangtan, Taojiang, Taoyuan, Shimen) on each river, we identified years when runoff changed abruptly (a hydrological event) in the time series using the Mann Kendall method, means of cumulative anomaly and sliding T test. The runoff time series was then divided into two stages, before and after the hydrological event, and then the composition of changes in environmental flow in the four rivers, before and after hydrological variation, were calculated and analyzed using IHA software. Results show that the environmental flow composition at each hydrological station in the four rivers changed to different degrees before and after the hydrological event. The deviation in the occurrence frequency of small floods at Xiangtan station of Xiangjiang River was the largest (77%.) The composition of environmental flow at Xiangtan station trended toward simplification, and the flows gradually merged into three types: small flood, high flow impulse and low flow, and the diversity of flow events decreased. There were no marked changes in environmental flow composition before and after hydrological events at Taojiang station. The degree of deviation in the occurrence of small floods at Taojiang station was the largest (150%). At Taoyuan station, large flood events increased after hydrological events, and the deviation in occurrence frequency of large floods was 150%, while small flood events decreased. For the environmental flow composition at Shimen station, large flood events and extreme low flow events clearly increased, the deviation in the frequency of extreme low flows was the largest (252%) . In a word, the environmental flow at Taojiang, Taoyuan and Shimen stations was more diverse than before hydrological events, and changes in flow were more abundant. Our research results provide a scientific basis for ecological protection and restoration in the watersheds of these four tributaries to Dongting Lake.