q ^tis the current soil moisture content, q _satis the saturated soil moisture content and q _dryis the residual soil moisture content.

The amount of evapotranspiration flux sourced from the unsaturated soil column is defined by

such that when the depth to watertable falls below dwt_deep metres the daily evapotranspiration flux is sourced entirely from the unsaturated soil column. By contrast the amount of evapotranspiration flux sourced from the saturated groundwater is defined by

Figure 1 shows the form of the weighting function that partitions evapotranspiration demand between the soil column and the groundwater system as described above.

Infiltration

Potential daily infiltration (q_avin ) is the sum of daily rainfall plus irrigation plus residual free standing water (infiltration excess from the previous time step) less evaporation. Evapotranspiration is a function of the available soil moisture based on the previous day's soil moisture content and a crop factor as previously described. It is assumed that when dry the soil is cracked resulting in an infiltration volume in excess of the saturated soil conductivity, Ksat .>/P>