Xie Qiancheng, Yang James, Lundström T Staffan
Fluid and Experimental Mechanics, Luleå University of Technology, 97187, Luleå, Sweden.
R&D Hydraulic Laboratory, Vattenfall AB, 81426, Älvkarleby, Sweden.
Sci Rep. 2021 Jul 1;11(1):13662. doi: 10.1038/s41598-021-93004-2.
The impoundment of the Three Gorges Dam on the Yangtze River begins in 2003 and a full pool level is first attained in 2010. This process leads to reciprocal adjustments in flow discharge, sediment transport and morphology downstream of the dam. Based on 26-year recorded hydrologic data 1990-2015 and surveyed bathymetries 1998, 2010 and 2015, this study elucidates, before and after the commissioning of the dam, the alterations along the 500-km reach of the river. Two-dimensional numerical simulations are performed to predict future morphological changes by 2025. The analyses demonstrate that the impoundment modulates the seasonal flow discharges and traps an appreciable amount of sediment, resulting in enhanced erosion potential and coarsening of sediment. On a multi-year basis, the maximum discharge varies by a factor of 1.3 and the corresponding suspended load concentration and transport rate differ by a factor of 3.0 and 3.8, respectively. Combinations of surveyed and simulated bathymetries reveal its morphological responses to the changes. A general pattern of erosion is observed along the reach. In its upper 120 km, the process slows down towards 2025. In the middle 200 km, the erosion shifts, following the gradual impounding, to slight deposition, which then shifts back to erosion around September 2018. In the final 180 km, erosion continues without any sign of de-escalation, which is presumedly ascribed to tidal actions. The reach has not yet achieved a hydro-morphological equilibrium; the riverbed down-cutting is supposed to continue for a while. The combination of the field and numerical investigations provides, with the elapse of time, insight into the morpho-dynamics in the 500 km river reach.
长江三峡大坝于2003年开始蓄水，2010年首次达到满蓄水位。这一过程导致大坝下游的流量、泥沙输移和地貌发生相互调整。基于1990 - 2015年26年的水文记录数据以及1998年、2010年和2015年的测量水深数据，本研究阐明了大坝运行前后，长江500公里河段的变化情况。通过二维数值模拟预测了到2025年的未来地貌变化。分析表明，蓄水调节了季节性流量，并拦截了大量泥沙，导致侵蚀潜力增强和泥沙粗化。在多年尺度上，最大流量变化系数为1.3，相应的悬沙浓度和输沙率分别相差3.0倍和3.8倍。实测和模拟水深数据的结合揭示了其对变化的地貌响应。沿该河段观察到普遍的侵蚀模式。在其上游120公里处，到2025年侵蚀过程减缓。在中游200公里处，随着逐渐蓄水，侵蚀转变为轻微淤积，然后在2018年9月左右又转变回侵蚀。在最后180公里处，侵蚀持续且没有任何缓和迹象，这可能归因于潮汐作用。该河段尚未达到水动力地貌平衡；河床下切预计还会持续一段时间。随着时间的推移，现场调查和数值研究的结合为500公里河段的地貌动力学提供了深入了解。
