Ebb-tidal jets: A model of suspended sediment and mass transport at tidal inlets

Mass transport by turbulent jets issuing from tidal inlets is investigated through a model that includes lateral mixing and entrainment, bottom friction, bathymetric changes, settling rate of particles (size), possible deposition/erosion at the bottom and ambient currents and concentrations. The bottom frictional jet becomes diluted more slowly than a classical jet. A non-vanishing concentration may result offshore and a maximum may occur in the core. The concentration of a jet on a sloping bottom decreases more rapidly due to increased dilution by entraiment. The effects of bottom friction and bottom slope compete in determining the jet concentration. Deposition to the bottom occurs within the jet mainly on both sides of the centre-line, and at lower rates on the centre-line. Erosion or deposition may occur at the jet core depending on the inlet flow conditions. In the case of erosion at the core, the material extracted is deposited on the margins and the offshore areas. Sorting of the sediments is expected, with coarser materials mainly deposited in the marginal areas, while the finer sediments are more uniformly distributed and jetted further off-shore. The main features of the model are verified through a limited set of observations. The qualitative agreement is enhanced for micro- and meso-tidal inlets that are dominated by tidal hydraulics.