The Evapotranspiration Segments package is like the Evapotranspiration package except that between the maximum and zero evapotranspiration rate, the relationship between head and evapotranspiration is a more complicated function of the head. The pane for the Evapotranspiration Segments package is on the MODFLOW Packages and Programs dialog box under Head Dependant Flux.
The user defines a table for each cell for containing the fraction of the maximum evapotranspiration rate and a fraction of extinction depth (measured down from the top). This table is used to calculate the evapotranspiration rate for heads between the evapotranspiration surface and the extinction depth. The user must specify how many segments are in the table. If there is only one segment in the table, the Evapotranspiration Segments package acts like the Evapotranspiration package except that the in ETS package, evapotranspiration can not be applied to the top active cell.
On the ETS: Evapotranspiration Segments package pane, the user can specify where the evapotranspiration will be applied. Possible choices include (1) the Top layer, (2) a Specified layer, and (3) the Top active cell. If Top active cell is specified, the location of evapotranspiration can move up or down as cells at the surface convert between dry and wet. If Specified layer is selected, the user can choose whether to use the layer of the object used to assign the rates for all the stress periods or to have the layer be specified separately for each stress period (Time varying ETS layers). The user can also specify parameters for the maximum evapotranspiration rate. The final maximum evapotranspiration rates will be the parameter value times a multiplier. Objects must be used to define the maximum evapotranspiration rates or maximum evapotranspiration rate multipliers.
In MODFLOW 6 models, "multipliers" can be used with evapotranspiration boundaries. Multipliers will be used if the "Use Multiplier (MODFLOW 6)" checkbox is checked.. Ordinarily, multipliers are not needed. If multipliers are used, the evapotranspiration rate is multiplied by the value of the multiplier. One use for multipliers might be when the evapotranspiration rates are defined using a time-series and it is desired to multiply the evapotranspiration rate values in the time series by a different amount at different locations.
Parameters are not required to define the maximum evapotranspiration rates but if parameters are defined, parameters must be used to define all the maximum evapotranspiration rates.
If more than one parameter of the same type applies to the same cell, the input value for MODFLOW will be the sum of the input values determined for that cell for all the parameters that apply to the cell. For example, suppose that there are two HK parameters defined: HK1 and HK2. They have Values of 10 and 20 respectively. If they both apply to the cell in column 1, row 1, layer 1 and neither has multiplier data sets, the hydraulic conductivity for that cell would be 10 + 20 = 30. Now suppose that the multiplier for HK1 was 5 at that cell. The hydraulic conductivity for that cell would be 10*5 + 20 = 70.
Parameters can also be edited in the Manage Parameters dialog box.
