Cross-shore suspended sediment transport under tidal currents

The transport of sediment over an intertidal mudflat by a cross-shore tidal current is investigated analytically by formulating a mathematical model of the fluid and particulate motion. The model exploits the low gradient of the intertidal flats and is based upon a shallow-layer approximation. It is found that the sediment transport comprises advection with the mean flow, deposition and erosion, if the flow speed is sufficiently high. A key step in the analysis is the conversion of the evolution equation for the concentration field to a Lagrangian frame of reference. This permits the analytical computation of the concentration of sediment following fluid particles and enables the construction of non-trivial periodic solutions for the concentration field and sediment flux throughout the tidal cycle. It is shown that the current transports sediment on-shore; this is the process of settling lag and indicates that the cross-shore flows tend to accrete sediment on the intertidal mudflats. Furthermore it is shown that the gradient of the intertidal flat is directly related to the supply of sediment and the amplitude of the tidal current.