User's guide of Proceessing Modflow 5.0

Processing Modflow 69
principal axes of the conductivity tensor must be parallel to the I and J-axes of your model grid,
if the anisotropy factor is not equal to 1. Note that anisotropy as referred here does not refer to
the ratio of horizontal to vertical hydraulic conductivity (see Leakance below)!
< Transmissivity
Fig. 3.14 The Layer Options dialog box
-1
MODFLOW requires transmissivity (=horizontal hydraulic conductivity [LT ] × layer thickness
[L]) for layers of type 0 or 2. If the Transmissivity flag is set to Calculated, PMWIN calculates
transmissivity by using user-specified horizontal hydraulic conductivity and the elevations of the
top and bottom of each layer. Set the Transmissivity flag to User Specified, if you want to
specify transmissivity manually.
< Leakance
For flow simulations involving more than one model layer, MODFLOW requires the input of the
vertical conductance term, known as vertical leakance (VCONT), between two model layers. Set
the Leakance flag of a layer to User Specified, if you want to specify the vertical leakance
between the layer and the underlaying layer directly. In the Data Editor, the vertical leakance
between the layers i and i+1 is given as the data of the layer i. A VCONT array is not required
for the bottom layer because MODFLOW assumes that the botton layer is underlain by
impermeable material. Setting the Leakance flag of a layer to Calculated causes PMWIN to
calculate VCONT by using the following rule.
As illustrated in Fig. 3.15a, when each model layer represents a different hydrostratigraphic
unit or when two or more model layers represent a single hydrostratigraphic unit, PMWIN uses
eq. 3.1 to calculate the vertical leakance VCONT.
3.4 The Grid Menu