Theory
Groundwater flow (i.e. the lower layer(s) in the soil profile is/are saturated with water) may optionally be chosen in the simulation as determined by the switch “GroundWaterFlow” in “Structure of Model”.
If groundwater is not considered, deep percolation, i.e. a vertical gravitational out flow of water from the lowest layer in the soil profile, may be estimated as a simple lower boundary to the unsaturated soil profile, as further described below. The lower boundary for the water equation can otherwise be calculated by either a given or an estimated value of the pressure head at the bottom of the profile, which in turn will generate deep percolation. These options for an unsaturated profile are determined by the switch LBoundUnSaturated.
Deep percolation can also optionally be assumed when there is a groundwater flow in the soil profile, i.e. when the lower part of the profile is saturated (see switch LBoundSaturated).
The groundwater flows, i.e. drainage, are considered a sink term in the one-dimensional structure of the model. There are several different approaches to account for water flows in various parts of the soil profile depending on the presence of artificial drainage systems and/or topographical and hydrogeological conditions (see switches EmpiricalDrainEq and PhysicalDrainEq). The empirical drainage equation is simpler than the physical equations and therefore it is usually used when there are no parameters available for the physical equation. It is possible to combine the empirical equation with a physical equation e.g. to let one of them symbolise an artificial drainage system. The total drainage from the system, qdr, is therefore the sum of the drainage calculated with the empirical and the physical drainage equation.
A groundwater source flow can optionally be simulated for saturated conditions, as described below. Pumping of water is also possible, and the amout of water removed by pumping is added to the total drainage. Vertical water flows in saturated layers is finally described at the end of the section.
Deep percolation,
unsaturated lower boundary
Deep percolation, saturated
lower boundary
Drainage, Simple empirical equations on groundwater
outflow
Drainage, Physical based equations on groundwater
outflow
Position of groundwater level and vertical redistribution
between the saturated layers