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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2018-524
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2018-524
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 19 Nov 2018

Research article | 19 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

Seasonal behaviour of tidal damping and residual water level slope in the Yangtze River estuary: identifying the critical position and river discharge for maximum tidal damping

Huayang Cai1,2,5, Hubert H. G. Savenije3, Erwan Garel4, Xianyi Zhang1,2, Leicheng Guo5, Min Zhang6, Feng Liu1,2, and Qingshu Yang1,2 Huayang Cai et al.
  • 1Institute of Estuarine and Coastal Research, School of Marine Engineering and Technology, Sun Yat-sen University, Guangzhou, China
  • 2Guangdong Provincial Engineering Research Center of Coasts, Islands and Reefs, Guangzhou, China
  • 3Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, the Netherlands
  • 4Centre for Marine and Environmental Research (CIMA), University of Algarve, Portugal
  • 5State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, China
  • 6Shanghai Normal University, Department of Geography, Shanghai, China

Abstract. As a tide propagates into the estuary, river discharge affects tidal damping primarily through a friction term, attenuating tidal motion by increasing the quadratic velocity in the numerator, while reducing the effective friction by increasing the water depth in the denominator. For the first time, we also demonstrate a third effect of river discharge that may lead to the weakening of the channel convergence (i.e., landward reduction of channel width and/or depth). In this study, monthly averaged tidal water levels (2003–2014) at six gauging stations along the Yangtze River estuary were used to understand the seasonal behaviour of tidal damping and residual water level slope. Observations show that there is a critical value of river discharge, beyond which the tidal damping is reduced with increasing river discharge. This phenomenon is clearly observed in the upstream part of the Yangtze River estuary (between the Maanshan and Wuhu reach), which suggests an important cumulative effect of residual water level on tide-river dynamics. To understand the underlying mechanism, an analytical model has been used to quantify the seasonal behaviour of tide-river dynamics and the corresponding residual water level slope under various external forcing conditions. It was shown that a critical position along the estuary is where there is maximum tidal damping (approximately corresponding to a maximum residual water level slope), upstream of which tidal damping is reduced in the landward direction. Moreover, contrary to the common assumption that larger river discharge leads to heavier damping, we demonstrate that beyond a critical value tidal damping is slightly reduced with increasing river discharge, owing to the cumulative effect of residual water level on the effective friction and channel convergence. Our contribution describes the seasonal patterns of tide-river dynamics in detail, which will, hopefully, enhance our understanding of the nonlinear tide-river interplay and guide effective and sustainable water management in the Yangtze River estuary and other estuaries with substantial freshwater discharge.

Huayang Cai et al.
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Short summary
Tide-river dynamics play an essential role in large-scale river deltas because they exert a tremendous impact on delta morphodynamics, salt intrusion, and deltaic ecosystems. For the first time, we illustrate that there is a critical river discharge, beyond which tidal damping is reduced with increasing river discharge and the underlying mechanism was explored by using an analytical model. The results are useful for guiding sustainable water managements and sediment transport in tidal rivers.
Tide-river dynamics play an essential role in large-scale river deltas because they exert a...
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