Position of groundwater level and vertical redistribution between the saturated layers

The groundwater level/saturation level is defined as the depth where the pressure head corresponds to atmospheric pressure. The saturation level z_sat is thereby given as:

                                                              (2.52)

where z_i is the depth of the middle of the layer i and ψ is the pressure head of the same layer. The layer with index i is located immediately above the uppermost fully saturated layer. Only one groundwater level is possible to simulate by the model. Horizontal drainage from this layer i is calculated until the pressure head will be lower than the distance to the adjacent midpoint of the layer below.

If full saturation will be obtained as a perched ground water above an unsaturated layer in the soil profile, the layer may reach saturation and also a possible over-saturation may occur with a pressure head higher that atmospheric pressure. This type of perched water table will not cause any net horisontal water flow, instead a vertical redistribution will take place towards layers with a lower pressure head.

For all saturated layers beneath the uppermost of the saturated layers the water content will always be exactly at saturation. No over-saturation will be allowed. All calculated net horizontal flows will be balanced by vertical redistributions to prevent non-saturated conditions. Vertical redistribution within the saturated zone is calculated based on the assumption that the water content will change only in the layer directly above the uppermost of the saturated layers.