UZF: Unsaturated-Zone Flow Package Pane

The UZF: Unsaturated-Zone Flow package pane is on the MODFLOW Features tab of the Object Properties dialog box.

The data that can be specified for the Unsaturated-Zone Flow package are the Starting time, Ending time, Infiltration rate, Evapotranspiration demand, ET extinction depth, and ET extinction water content. The user can also choose what data to print about the unsaturated zone for the cells whose values are set by the object that is being edited.

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

Infiltration rate is the infiltration rates (L/T) at land surface for each vertical column of cells. If the Infiltration rate is specified as being greater than the vertical hydraulic conductivity then the Infiltration rate is set equal to the vertical unsaturated hydraulic conductivity. Excess water is routed to streams or lakes when IRUNFLG is not zero and the Streamflow Routing or Lake package is active.

Evapotranspiration demand is the evapotranspiration (ET) demand rate (L/T) within the ET extinction depth interval for each vertical column of cells.

ET extinction depth, is the depth below land surface below which ET does not occur. The quantity of Evapotranspiration (ET) removed from a cell is limited by the volume of water stored in the unsaturated zone above the extinction depth. If groundwater is within the ET extinction depth, then the rate removed is based on a linear decrease in the maximum rate at land surface and zero at the ET extinction depth. The linear decrease is the same method used in the Evapotranspiration Package (McDonald and Harbaugh, 1988, chap. 10).

ET extinction water content is the water content below which ET cannot be removed from the unsaturated zone. The ET extinction water content must have a value between (Saturated_Water_Content-Sy) and Saturated_Water_Content, where Sy is the specific yield specified in either the LPF or BCF Package.

The user may also choose to print certain data in output files with the extension .uzfg. The choices provided by the UZF package through the IUZOPT variable are

1.Print

•time,

•groundwater head, and

•thickness of unsaturated zone, and

•cumulative volumes of infiltration,

•recharge,

•storage,

•change in storage and

•groundwater discharge to land surface.

2.Print the items in option 1 and also print

•rates of infiltration,

•recharge,

•change in storage, and

•groundwater discharge.

3.Print

•time,

•groundwater head,

•thickness of unsaturated zone, followed by a series of

•depths and

•water contents in the unsaturated zone.