Abstract
The hydrological pattern changes have a great influence on the wetland environment. However, some important wetland areas often lack historical observations due to economic and physical conditions. The Tian-e-Zhou oxbow lake wetland is an important habitat for two endangered species and also has very little historical hydrological data. Remote sensing images can be used to explore the historical water area fluctuation of lakes. In addition, remote sensing can also be used to obtain historical water levels based on the water boundary elevation integrated with a topographic data (WBET) method or the level-surface area relationship curve (LRC) method. In order to minimize the uncertainty of the derived results, both methods were introduced in the extraction of the water level of Tian-e-Zhou during 1992–2015. The results reveal that the hydrological regime of the oxbow lake has experienced a significant change after the Shatanzi Levee construction in 1998. With the impact of the levee, the mean annual water surface area of the lake was reduced by 5.8 km2 during the flood season, but, during the non-flood season, it was increased by 1.35 km2. For the same period, the water level of the lake during the flood season also showed a 1.47 m (WBET method) or 3.21 m (LRC method) decrease. The mean annual water level increased by 1.12 m (WBET method) or 0.75 m (LRC method). Both results had a good accuracy with RMSE (root-mean-square errors) of less than 0.4 m. Furthermore, the water level differences between the Yangtze River channel and the oxbow lake increased by at least 0.5 m. It is found that the hydrological pattern of the oxbow lake changed significantly after the levee construction, which could bring some disadvantages to the habitats of the two endangered species.
Highlights
The lower Jingjiang reach of the Yangtze River is known for its meanders with a high degree of channel sinuosity [1,2]
We focused on the application of remote sensing technology in determining the hydrologic pattern changes of an oxbow lake in the middle reach of the Yangtze River
The results show that all of the curves produced a good fit for the relationship between the water level and the lake surface area in the Tian-e-Zhou oxbow lake (Table 1)
Summary
The lower Jingjiang reach of the Yangtze River is known for its meanders with a high degree of channel sinuosity [1,2]. With the implementation of some major water projects, including the Three Gorges Dam and the Gezhouba Dam [5,6], as well as river regulation and flood control projects [7,8], the hydrologic regime in the lower Jingjiang reach and the oxbow lakes have been greatly altered in recent decades. In-situ data obtained from gauged hydrological stations can be applied to analyze the hydrological changes in rivers and lakes. Limited by the underdeveloped infrastructure and the complex underlying surfaces, hydrological station networks in the middle reach of the Yangtze River. Basin are sparse and poorly maintained [9,10,11] In these ungauged basins and regions, especially in the oxbow lakes, historical or long-time series of hydrological data are either lacking or difficult to obtain. Many oxbow lakes in the middle reach of the Yangtze River Basin maintained abundant endangered species. Despite the fact that hydrologic changes have a great influence on the habitats of these endangered species, no study has fully addressed the hydrologic changes in this area
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