Value

Meaning

Constant Psi

The lower boundary for water equation is calculated from the assumption of a constant pressure head of the bottom layer. The pressure head is given by the value of a parameter.

Constant Maximum Psi

The lower boundary for water equation is calculated from the assumption of a constant pressure head of the bottom layer if an excess of water appear in the lower layer. The pressure head is then given by the value of a parameter. Otherwise the lower boundary will be defined by a zero flow, i.e., no capillary flow from the soil below the lowest layer is allowed.

Dynamic Psi

Similar as “Constant Psi” but the pressure head of the bottom layer is specified as a dynamic variable by using a PG driving variable file where the value of the pressure head is given.

No Flow

No deep percolation. The lower boundary completely impermeable.

Unit Grad Flow

The water flow from the bottom layer is calculated from the unsaturated conductivity of the bottom layer and assuming a unit gradient gravitational flow.