In addition to the standard saturated zone module FLAIRS a module has been developed to account for variations in groundwater density, primarily significant for coastal areas. This variable density version, FLAIRSVD, has the same options and possibilities when calculating groundwater flow as the standard version. The only difference is that the user defines the density distribution beforehand, which is then accounted for in the calculations.

How variable density is incorperated

The effect of variable density on groundwater flow is accounted for by assigning correction fluxes to the individual nodes. The correction fluxes depend on the geometry of the aquifers and the density distribution (fresh/salt distribution) and can be determined in advance. Using these correction fluxes together with the usual boundary conditions, e.g. topsystem and watercourses, groundwater flow can be calculated.

Change of density distribution with time

The density distribution is assumed not to change much during the simulated period. So that transient simulation runs as well as pathline calculations are accounting for the variable density of the groundwater. Changes of the density distribution as a result of advection can therefor still be determined. This method has proofed more than sufficient for coastal areas and other areas where differences in density of the groundwater is of importance.