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Input grid(s) for transport of constituents

With SWASH some transport phenomena of constituents can be simulated that result from tidal, wind and wave forcing in stratified flows. The considered constituents are salinity, temperature and suspended sediment load. The presence of these constituents will influence the density of water and consequently, they will induce flow through the baroclinic pressure gradient. In this way, transport of constituents and water flow are coupled. Examples are salt intrusion in an estuary, sediment transport in turbidity flows and transport of dissolved matter in lakes and rivers.


Only the background temperature is considered in the model, and the heat exchange flux at the air-water interface is not taken into account.


With respect to the sediment transport, the following assumptions are made.

The inclusion of transport of constituent in SWASH must be done by means of an input grid for each constituent. Such an input grid represents the ambient or background concentration of the corresponding constituent as an initial state, while it provides information along the open boundaries of the computational domain. The use of this information to impose a boundary condition for constituent depends on the flow direction. At inflow, the concentration is prescribed using this information delivered by the input grid. At outflow, the concentration is determined solely by the concentration in upstream part of the domain due to pure advection. It is assumed that the area of interest in which transport phenomena occur is far away from the open boundaries. The ambient concentration at open boundaries is therefore supposed to be steady state. However, for unsteady salt intrusion in a tidal inlet, the concentration is prescribed at inflow by means of a so-called Thatcher-Harleman boundary condition. In this way, a smooth (sinusoidal) transition from the outflow concentration to the inflow boundary condition can be described; see also command TRANSPORT.


It is advised to make an input grid so large that it completely covers the computational grid. Otherwise, SWASH assumes that in the region outside the input grid, the constituent equals to the value at the nearest boundary of the input grid (lateral shift of that boundary).


Finally, both the initial state and boundary conditions of any constituent may be vary in the vertical direction. This needs to be provided to SWASH with an input grid for each vertical layer.


next up previous index
Next: Output grids Up: Choice of grids and Previous: Input grid(s) and time   Index
The SWASH team 2017-04-06