State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing, 210098, China.
College of Harbor, Coastal and Offshore Engineering, Hohai University, Nanjing, 210098, China.
Sci Rep. 2020 Apr 14;10(1):6304. doi: 10.1038/s41598-020-62432-x.
The Yangtze River Estuary (YRE) is one of the world's largest river-tidal systems with rapidly changing hydrology and morphology following the construction of multiple dams. The effects of dam construction may extend to the region close to the coast, where channel stability depends on the asymmetry of the tide. Here, we focus on the possible effects of changing discharge regimes on tidal asymmetry in the YRE. Specifically, we focus on the difference in duration between ebb and flood, quantified as tidal duration asymmetry, because it has strong implications for residual sediment transport and can be derived from available water level data. To cope with nonstationary tides under the influence of a time-varying river discharge, a nonstationary harmonic analysis tool (NS_TIDE) is applied to explore the spatiotemporal variations in tidal duration asymmetry, under the influence of different combinations of tidal constituents. Tidal duration asymmetry initially increases, then slightly decreases, in an upstream direction. It experiences significant seasonal variations in response to rapidly varying discharge: tides are more asymmetric upstream of Zhenjiang in the dry season and more asymmetric downstream in the wet season. The combined effects of discharge regulation and morphological changes cause seasonal alterations in tidal duration asymmetry. In the wet season, reduced river discharge caused by water storage and climate change enhance the asymmetry upstream (+11.74% at Wuhu, +7.19 at Nanjing) while the asymmetry is weakened downstream (-2.90% at Zhenjiang, -7.19 at Jiangyin) following the TGD's operation. Downstream channel erosion caused by post-TGD lower sediment loads has become the dominant factor weakening tidal asymmetry in most parts of the YRE in the dry season. Understanding these evolutions of tidal duration asymmetry under the hydrological and morphological effects has important implications for the management of estuarine ecosystem and navigation.
长江河口（YRE）是世界上最大的河流潮汐系统之一，随着多座大坝的建设，其水文学和地貌形态迅速发生变化。大坝建设的影响可能会延伸到靠近海岸的地区，而那里的航道稳定性取决于潮汐的不对称性。在这里，我们专注于改变流量模式对 YRE 潮汐不对称性的可能影响。具体来说，我们关注的是涨潮和落潮之间持续时间的差异，用潮汐持续时间不对称性来量化，因为它对剩余泥沙输移有很强的影响，并且可以从可用的水位数据中得出。为了应对受时变河流流量影响的非平稳潮汐，应用非平稳调和分析工具（NS_TIDE）来探索在不同潮汐成分组合的影响下，潮汐持续时间不对称性的时空变化。潮汐持续时间不对称性最初沿上游方向增加，然后略有减小。它对流量的快速变化表现出显著的季节性变化：在旱季，镇江上游的潮汐更不对称，而在雨季，下游的潮汐更不对称。流量调节和地貌变化的综合影响导致潮汐持续时间不对称性的季节性变化。在雨季，由于蓄水和气候变化导致的河流径流量减少，在上游增加了潮汐的不对称性（在芜湖增加了+11.74%，在南京增加了+7.19%），而在三峡工程运行后，下游的潮汐不对称性减弱（在镇江减弱了-2.90%，在江阴减弱了-7.19%）。三峡工程后较低的泥沙负荷导致下游河道侵蚀，已成为旱季大部分长江河口潮汐不对称性减弱的主要因素。了解这些潮汐持续时间不对称性在水文和地貌影响下的演变，对河口生态系统和航运管理具有重要意义。
