UZF6: Unsaturated-Zone Flow Package for MODFLOW 6

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The UZF6: Unsaturated-Zone Flow Package for MODFLOW 6 pane is on the MODFLOW Features tab of the Object Properties dialog box.

The pane has two tabs: one for properties that do not vary with time (Steady properties) and the other for properties that do vary with time (Time varying properties).

hmtoggle_plus1Steady properties

Surface depression depth (surfdep): When the water table is above the top of a cell at the ground surface, infiltration is gradually reduced to zero until the water table rises above the tops of any surface depressions on the ground surface.

Saturated Kz (vks): The unsaturated vertical hydraulic conductivity (Kunsat) is related to the saturated  vertical hydraulic conductivity (Ksat) through the Brooks Corey equation. Kunsat = Ksat [(θ - θresid) / (θsat - θresid)]ε

Residual water content (thtr) The residual water content is θresid in the Brooks Corey equation.

Saturated water content (thts) The saturated water content is θrsat in the Brooks Corey equation.

Initial water content (thti) The initial water content of the UZF cell.

Brooks Corey epsilon (eps) The Brooks Corey epsilon is ε in the Brooks Corey equation.
hmtoggle_plus1Time varying properties

Starting time and Ending time are explained in the help for the MODFLOW Features tab.

Infiltration (finf) is the applied infiltration rate (L/T). If the applied infiltration rate is larger than the vertical hydraulic conductivity, the actual infiltration will be reduced to the vertical hydraulic conductivity. Any remaining potential infiltration will be available to the MVR package as rejected infiltration.

Potential ET (pet) is the potential evapotranspiration rate of the UZF cell and specified groundwater flow (GWF) cell. Evapotranspiration is first removed from the unsaturated zone and any remaining potential evapotranspiration is applied to the saturated zone. If the UZF cell overlies another UZF cell, then residual potential evapotranspiration not satisfied in the UZF cell is applied to the underlying UZF and GWF cells. PET is always specified but is only used if evapotranspiration is specified in the UZF 6 OPTIONS block.

Extinction depth (extdp) is the evapotranspiration extinction depth of the UZF cell. If the UZF cell overlies another UZF cell and EXTDP extends below the GWF cell bottom then remaining potential evapotranspiration is applied to the underlying UZF and GWF cells.  EXTDP is always specified but is only used if evapotranspiration is specified in the UZF 6 OPTIONS block.

Extinction water content (extwc) When the water content is at or below the extinction water content, no evapotranspiration will be simulated for the cell.  EXTWC is always specified but is only used if evapotranspiration is specified in the UZF 6 OPTIONS block.

Air entry potential (ha) is the air entry potential (head) of the UZF cell. HA is always specified, but is only used if evapotranspiration is simulated and the  UNSAT_ETAE option is specified in the UZF 6 OPTIONS block.

Root potential (hroot) is the root potential (head) of the UZF cell. HROOT is always specified, but is only used if evapotranspiration is simulated and  theUNSAT_ETAE is specified in the UZF 6 OPTIONS block.

Root activity (rootact) is the root activity function of the UZF cell. ROOTACT is the length of roots in a given volume of soil divided by that volume. Values range from 0 to about 3 cm-2, depending on the plant community and its stage of development. ROOTACT is always specified, but is only used if evapotranspiration is simulated and UNSAT_ETAE is specified in the OPTIONS block.