Preprints
https://doi.org/10.5194/os-2021-58
https://doi.org/10.5194/os-2021-58

  08 Jul 2021

08 Jul 2021

Review status: this preprint is currently under review for the journal OS.

Dynamics of fortnightly water level variations along a tide-dominated estuary with negligible river discharge

Erwan Garel1, Ping Zhang2, and Huayang Cai2 Erwan Garel et al.
  • 1Centre for Marine and Environmental Research (CIMA), University of Algarve, Faro, Portugal
  • 2Institute of Estuarine and Coastal Research, School of Marine Engineering and Technology, Sun Yat-sen University, Guangzhou 510275, China

Abstract. Observations indicate that the fortnightly fluctuations in mean water level increase in amplitude along the lower half of a tide-dominated estuary (The Guadiana estuary) with negligible river discharge but remain constant upstream. Analytical solutions reproducing the semi-diurnal wave propagation shows that this pattern results from reflection effects at the estuary head. The phase difference between velocity and elevation increases from the mouth to the head (where the wave has a standing nature) as the high and low water levels get progressively closer to slack water. Thus, the tidal (flood-ebb) asymmetry in discharge is reduced in the upstream direction. It becomes negligible along the upper estuary half, as the mean sea level remains constant despite increased friction due to wave shoaling. Observations of a flat mean water level along a significant portion of an upper estuary, easier to obtain than the phase difference, can therefore indicate significant reflection of the propagating semi-diurnal wave at the head. Details of the analytical model shows that changes in the mean depth or length of semi-arid estuaries, in particular for macrotidal locations, affect the fortnightly tide amplitude, and thus the upstream mass transport and inundation regime. This has significant potential impacts on the estuarine environment.

Erwan Garel et al.

Status: open (until 03 Sep 2021)

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Erwan Garel et al.

Erwan Garel et al.

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Short summary
Understanding the tidal hydrodynamics is essential for water resources management in estuarine environment. In this study, we propose an analytical model to examine the fortnightly water level variations due to tidal motions alone in tide-dominated estuaries. Details of the analytical model shows that changes in the mean depth or length of semi-arid estuaries affect the fortnightly tide amplitude, which has significant potential impacts on the estuarine environment.