The equation used to calculate the water amount percolating from a layer to the layer below follows:

where Δt is the time step duration (hour), and TTperc is the percolation travel time (hour-1). Other terms are defined in cascading approach.

The percolation travel time is computed for each layer, as:

where SATly is the water amount of the soil layer at saturation (mm H2O), FCly is the water content of the soil layer at field capacity (mm H2O) and Ksat is the saturated hydraulic conductivity of the current layer (mm h-1). SATly and FCly values are computed multiplying the volumetric fraction values for the layer thickness (mm).

Symbols and algorithms are partially derived from the SWAT model (Neitsch et al., 2000).

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