Infiltration and leakage

It is possible to calculate the net infiltration rate by a simplified model that describes the infiltration from the free surface zone to the unsaturated zone and the leakage from the unsaturated zone to the saturated zone. This way the model can e.g. account for a decreased storage capacity due to previous rainfall events.

The model assumes the following:

·         The unsaturated zone is modelled as an infiltration zone with constant porosity over the full depth of the zone.

·         The infiltrated volume between the free surface zone and the infiltration zone is based on a constant flow rate,
i.e. V_infiltration = Q_i×Dt where Q_i is the prescribed infiltration rate.

·         The leaked volume between the saturated and unsaturated zone is also based on a constant flow rate,
i.e. V_leakage = Q_l×Dt where Q_l is the prescribed leakage rate.

Figure 6.15        Definition of infiltration with storage and leakage

Note: The infiltration flow cannot exceed the amount of water available in the free surface water zone nor the difference between the water capacity of the infiltration zone and the actual amount of water stored there. It is possible that the infiltration flow completely drains the free surface zone from water and thus creates a dried-out point in the two-dimensional horizontal flow calcula­tions.