User's guide of Proceessing Modflow 5.0

218 Processing Modflow
< To specify Aquifer Top
1. Select Grid < Top of Layers (TOP)
2. Since the aquifer top elevation is uniform throughout the model it is possible to set a single
value to the entire grid by Value < Reset Matrix...
3. Enter 25 in the Reset Matrix dialog box and click OK to exit.
4. Leave the Data Editor by File < Leave Editor < Yes
Repeat the above process to set the elevation of the base of the aquifer to 0m.
Aquifer parameters
The next stage is to assign the aquifer parameters.
< To specify the horizontal hydraulic conductivity
1. Select Parameters < Horizontal Hydraulic Conductivity
2. Since the horizontal hydraulic conductivity is uniform throughout the model it is possible
to set a single value to the entire grid by Value < Reset Matrix...
3. Enter 160 in the Reset Matrix dialog box and click OK to exit.
4. Leave the Data Editor by File < Leave Editor < Yes
Initial Conditions
MODFLOW requires some initial hydraulic head conditions to enable it to perform the flow
simulation. In a steady state flow model only the hydraulic head values of the fixed-head cells
are important as these do not change throughout the simulation. In a transient simulation
however, the hydraulic heads at the start of the simulation are the basis for determining the
resulting head distribution after the aquifer is subjected to some time-based stresses. It is usual
to perform a steady state flow simulation use the resulting head distribution as the basis for the
transient simulations, which is what we shall do in this case.
< To set the initial hydraulic heads
1. Select Parameters < Initial Hydraulic Heads
2. Firstly set the entire grid to a uniform value by Value < Reset Matrix...
3. Enter 16 in the Reset Matrix dialog box and click OK to exit.
4. Now set hydraulic head of the northern fixed-head boundary to 15 metres by firstly
selecting the top left cell [1,1,1] with the left mouse button and then assign a value of 15 by
6.1.1 Tutorial 1 - Unconfined Aquifer System with Recharge