Transient Simulations require:

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Transient Simulations require

• Initial Conditions

• Storage Coefficient

• Time step

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General 3D equation
Heterogeneous, anisotropic, transient,
sink/source term
Specific storage Ss S/b S is storativity or
specific yield
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Types of Initial Conditions

• Static steady state
• Dynamic steady state
• Dynamic cyclic conditions
• (Time distant conditions)

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Problem set 5 part 7.3b
Generating cyclic steady state conditions
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from GWV
Remember In MODFLOW, a layer is considered
confined when the head in the cell is above the
top of the cell. (If the top layer is specified
to be unconfined, it has no top elevation.)
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• MODFLOW allows for two types
• of storage coefficients
• Unconfined storage coefficient (i.e., specific
  yield)
• (used for unconfined layers)
• Confined storage coefficient
• (used for confined layers)
• or you may input specific storage, Ss

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A convertible layer in MODFLOW (laycon type
3) is one where cells can convert from confined
to unconfined conditions. (Conversion back to
confined is possible with the re-wetting
option but this option doesnt always work and
may give incorrect solutions. Use with caution,
or not at all.)
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MODFLOW divides time into Stress Periods. There
are multiple time steps in a stress period.
Initial ?t
Parameters in the following packages can be
changed between stress periods WEL, RCH, RIV,
DRN, EVT, GHB
Rule of thumb take at least five time steps per
stress period.
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MODFLOW divides time into Stress Periods. There
are multiple time steps in a stress period.
Initial ?t
Rule of thumb take at least five time steps per
stress period.
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Selecting the time step Can
use ?t Sa2/4T for the initial time step of a
stress period or find an appropriate time step by
trial and error.