User's guide of Proceessing Modflow 5.0

80 Processing Modflow
When the hydraulic head (h) in a drain-cell is greater than the drain elevation, water flows into
the drain and is removed from the groundwater model. Discharge to the drain is zero when the
hydraulic head is lower than or equal to the median drain elevation. Recharge from the drain is
always zero, regardless of the hydraulic head in the aquifer. Discharge rate to the drain (Q ) is
d
calculated by
Q d ' C d · (h & d)
The value C of a drain-cell is often given by
d
C d ' K · L
3.6.1 MODFLOW
(3.5)
(3.6)
where L is the length of the drain within a cell. The value K is a equivalent hydraulic conductivity
describing all of the head loss between the drain and the aquifer. It depends on the material and
characteristics of the drain itself and the immediate environment. The value C is usually
d
unknown and must be adjusted during a model calibration.
MODFLOW < Evapotranspiration
The Evapotranspiration package simulates the effects of plant transpiration and direct
evaporation in removing water from the saturated groundwater regime. Evapotranspiration is
defined by assigning the following data to each vertical column of cells in the
Evapotranspiration Package dialog box (Fig. 3.17) of the Data Editor:
-1
- Maximum ET Rate R ETM [LT ],
- Elevation of the ET Surface h s [L],
- ET Extinction Depth d [L],
- Layer Indicator I [-], and
ET
- Parameter Number [-]
The specified values are shown from left to right on the status bar. These values are constant
during a given stress period. For transient flow simulations involving several stress periods, these
values can be different from period to period. Note that although the values are specified for each
vertical column of cells, you may move to other layers within the Data Editor and examine the
grid configuration in each layer. The parameter number is used to assign R as a parameter for
ETM
an automatic calibration by the inverse models PEST or UCODE, see PEST < Parameter List...
or UCODE < Parameter List....