User's guide of Proceessing Modflow 5.0

82 Processing Modflow
1. Evapotranspiration is always drawn from the top layer of the model.
2. Vertical distribution of evapotranspiration is specified in the Layer Indicator Array. I ET
defines the layer where evapotranspiration is drawn from.
In either case the Q has no influence on the simulation if the designated cell is either a no-flow
ET
(inactive) cell or a constant head cell. You can select an option in the Evapotranspiration
Package dialog box. The layer indicator array is needed only when the second option is used.
MODFLOW < General-Head Boundary
The General-Head Boundary package is used to simulate head-dependent flow boundaries
(Cauchy boundary conditions). Similar to the Drain package, a General-Head Boundary cell
(GHB-cell) is defined by three cell values:
2 -1
- GHB hydraulic conductance C b [L T ]
- Hydraulic head at the boundary h b [L]
- Paramter Number [-]
The parameter number is used to assign C as a parameter for an automatic calibration by the
b
inverse models PEST or UCODE, see PEST < Parameter List... or UCODE < Parameter
List....
3 -1
Flow through the general-head boundary Q b [L T ] is calculated by
Q b ' C b (h b & h)
3.6.1 MODFLOW
(3.9)
where h is the hydraulic head in the aquifer. A GHB-cell is equivalent to a constant head cell,
if a very large C is used. The values C and h are constant during a given stress period. For
b b b
transient flow simulations involving several stress periods, these values can be different from
period to period. This allows you to change the head at "constant-head" boundaries as the
transient simulation progresses.
MODFLOW < Horizontal-Flow Barrier
The Horizontal-Flow Barrier package simulates thin low-permeability geologic features, such
as vertical faults or slurry walls, that impede the horizontal flow of groundwater. These geologic
features are approximated as a series of horizontal-flow barriers conceptually situated on the