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Three‐Dimensional Sediment Dynamics in Well‐Mixed Estuaries: Importance of the Internally Generated Overtide, Spatial Settling Lag, and Gravitational Circulation
Author(s) -
Wei Xiaoyan,
Kumar Mohit,
Schuttelaars Henk M.
Publication year - 2018
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2017jc012857
Subject(s) - shoal , sediment , estuary , sediment transport , settling , geology , advection , hydrology (agriculture) , sedimentary budget , turbidite , oceanography , geomorphology , environmental science , geotechnical engineering , physics , environmental engineering , thermodynamics
To investigate the dominant sediment transport and trapping mechanisms, a semi‐analytical three‐dimensional model is developed resolving the dynamic effects of salt intrusion on sediment in well‐mixed estuaries in morphodynamic equilibrium. As a study case, a schematized estuary with a converging width and a channel‐shoal structure representative for the Delaware estuary is considered. When neglecting Coriolis effects, sediment downstream of the estuarine turbidity maximum (ETM) is imported into the estuary through the deeper channel and exported over the shoals. Within the ETM region, sediment is transported seaward through the deeper channel and transported landward over the shoals. The largest contribution to the cross‐sectionally integrated seaward residual sediment transport is attributed to the advection of tidally averaged sediment concentrations by river‐induced flow and tidal return flow. This contribution is mainly balanced by the residual landward sediment transport due to temporal correlations between the suspended sediment concentrations and velocities at the M 2 tidal frequency. The M 2 sediment concentration mainly results from spatial settling lag effects and asymmetric bed shear stresses due to interactions of M 2 bottom velocities and the internally generated M 4 tidal velocities, as well as the salinity‐induced residual currents. Residual advection of tidally averaged sediment concentrations also plays an important role in the landward sediment transport. Including Coriolis effects hardly changes the cross‐sectionally integrated sediment balance, but results in a landward (seaward) sediment transport on the right (left) side of the estuary looking seaward, consistent with observations from literature. The sediment transport/trapping mechanisms change significantly when varying the settling velocity and river discharge.