Upward flux is the rate of water movement upward from the water table.  Upward flux is synonymous with the term capillary movement.  This value is quite important since there may be insufficient water in the root zone for PET.  In these cases the upward flux into the root zone may limit ET causing stress to the crop.  Values of upward flux corresponding to various water table depths are input in the Drain Vol - Upflux tab of the Soil input screen.

 

Upward flux may be determined mathematically from the unsaturated hydraulic conductivity functions of the soil horizons.  These functions can be estimated from the soil water characteristics and the saturated "K" values using the soil preparation program.  The last value for depth to the water table MUST be 1000 cm and 0 for upward flux.