Variations of Runoff and Sediment Load in the Middle and Lower Reaches of the Yangtze River, China (1950-2013).

Na Li,Xutong Wu,Dong Wang,Lachun Wang,Chunfen Zeng,Dengfeng Liu,Maite Decastro

doi:10.1371/journal.pone.0160154

Na Li, Xutong Wu + Show 5 more

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https://doi.org/10.1371/journal.pone.0160154

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Abstract

On the basis of monthly runoff series obtained in 1950–2013 and annual sediment load measured in 1956–-2013 at five key hydrological stations in the middle and lower reaches of the Yangtze River basin, this study used the Mann-Kendall methods to identify trend and abrupt changes of runoff and sediment load in relation to human activities. The results were as follows: (1) The annual and flood season runoffs showed significant decreasing trends at Yichang station, and showed slight downward trends at Hankou and Datong stations, while the abrupt changes of dry season runoff at Yichang, Hankou and Datong stations occurred in about 2007 and the change points were followed by significant increasing trends. The construction of the Three Gorges Dam, which began to operate in 2003, influenced the variations of runoff in the mainstream of Yangtze River, but the effect weakened with the distance along the downstream direction from TGD. (2) Since the 1990s, annual sediment loads at Yichang, Hankou, and Datong stations have been decreasing significantly, and after 2002, the annual sediment load at Yichang dropped below that of Hankou and Datong. The dams and deforestation/forestation contributed to the significant decreasing trend of the sediment load. In addition, the Three Gorges Dam aggravated the downward trend and caused the erosion of the riverbed and riverbanks in the middle and lower reaches. (3) The runoff and sediment load flowing from Dongting Lake into the mainstream of the Yangtze River showed significant decreasing trends at Chenglingji station after 1970s, and in contrast, slight increase in the sediment flow from Poyang Lake to the mainstream of the Yangtze River at Hukou station were detected over the post-TGD period (2003–2013). The result of the study will be an important foundation for watershed sustainable development of the Yangtze River under the human activities.

Highlights

Rivers play a significant role in the transport of sediment from land to the ocean affecting the evolution of the river deltas itself, which must be seen as a key pathway for material transfer on the Earth [1,2]
The Three Gorge Dam intensified the decreasing trend of the annual runoff and annual sediment load in the mainstream, and the impact decreased with the increasing distance between the Three Gorges Dam and the hydrological stations
After the impoundment of the Three Gorges Dam (TGD), the runoff and sediment load outflow from Dongting Lake towards the main river at Chenglingji decreased, and in addition, the average frequency of the backflow of the Yangtze River as well as the quantity of water and sediment backflow lowered and the amount of sediments transported from Poyang Lake into mainstream started to increase

Summary

Introduction

Rivers play a significant role in the transport of sediment from land to the ocean affecting the evolution of the river deltas itself, which must be seen as a key pathway for material transfer on the Earth [1,2]. A large number of researchers in the world attached great importance to the trend detection in hydrological series, such as sediment load and streamflow series at the basin scale [14,15,16,17,18]. This is especially important in China, where few rivers are in a natural or semi-natural condition, with disturbances causing substantial changes to runoff and sediment regimes [19]

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