Variation behavior of tidal dynamics in the Yangtze Estuary: implying the amplification of hydrodynamics and sediment dynamics by the human intervention

During the last decades, many estuarine systems in Europe (e.g. the Elbe, Ems, Loire) have shown increases in tidal range and in turbidity, which are linked to local human activity (i.e., deepening). Compared to these European estuaries, the Yangtze Estuary is much larger in scales, experiences much stronger river discharge, and it is subject to a strong seasonal variation in freshwater and sediment supply from the drainage area. Moreover, the Yangtze estuary is a complex network with several branches, connecting channels. The changes in the flow and sediment dynamics in the estuary may result from both local and nonlocal human activities. Despite the intense research efforts over the past two decades, it is still unclear which impact (local or nonlocal) is responsible for the changing flow and sediment characteristics in the estuary. Deep investigation of tidal characteristic quantities such as extreme tidal level, tidal range, amplitude of tidal constituents, tidal characteristic coefficient and suspended sediment concentration is performed in a systematic manner. It is accomplished using the extreme value analysis, the wavelet analysis and harmonic analysis of water level at 11 hydrography stations along the tidal river channel (Datong-Nanjing reach) and estuarine section (downstream the Xuliujing) during 2008-2016. Similar data analysis is also performed for the last four decades of 20th century and results are compared with the analysis of the recent measurements. The driving forces of the significant changes in tidal characteristic quantities and suspended sediment concentration are discussed. Results show that the tidal dynamics in the Yangtze estuary has been enhanced. Its seasonal variation is attributed to the adjustment of runoff distribution, which is mainly caused by the operation of Three Gorges Dam. In short-term, local changes of flow/sediment dynamics, terrain changes play a major role. In the long term (on the 40-year time scale), the effect of sea level rise on the increasing M2 constituent is obvious. This has mainly resulted from the enhancing anti-clockwise rotation of the synchronous tidal phase.