Salt Dynamics in Well-Mixed Estuaries

Salt Dynamics in Well-Mixed Estuaries: Importance of Advection by Tides

Wei, X. (TU Delft Mathematical Physics)
Schuttelaars, H.M. (TU Delft Mathematical Physics)
Schramkowski, G.P. (Flanders Hydraulics Research)

2016-05-01

Understanding salt dynamics is important to adequately model salt intrusion, baroclinic forcing, and sediment transport. In this paper, the importance of the residual salt transport due to tidal advection in well-mixed tidal estuaries is studied. The water motion is resolved in a consistent way with a width-averaged analytical model, coupled to an advection–diffusion equation describing the salt dynamics. The residual salt balance obtained from the coupled model shows that the seaward salt transport driven by river discharge is balanced by the landward salt transport due to tidal advection and horizontal diffusion. It is found that the tidal advection behaves as a diffusion process, and this contribution is named tidal advective diffusion. The horizontal diffusion parameterizes processes not explicitly resolved in the model and is called the prescribed diffusion. The tidal advective diffusion results from the correlation between the tidal velocity and salinity and can be explicitly calculated with the dominant semidiurnal water motion. The sensitivity analysis shows that tidal advective diffusivity increases with increasing bed roughness and decreasing vertical eddy viscosity. Furthermore, tidal advective diffusivity reaches its maximum for moderate water depth and moderate convergence length. The relative importance of tidal advective diffusion is investigated using the residual salt balance, with the prescribed diffusion coefficient obtained from the measured salinity field. The tidal advective diffusion dominates the residual salt transport in the Scheldt estuary, and other processes significantly contribute to the residual salt transport in the Delaware estuary and the Columbia estuary.

Circulation/ Dynamics
Buoyancy
Diffusion
Fluxes
Mass fluxes/transport
Mixing
Shallow-water equations

http://resolver.tudelft.nl/uuid:9c8c9304-5bd0-4ca9-a0b9-b9c718d6b492

https://doi.org/10.1175/JPO-D-15-0045.1

0022-3670

Journal of Physical Oceanography, 46 (5), 1457-1475

Institutional Repository

journal article

© 2016 X. Wei, H.M. Schuttelaars, G.P. Schramkowski