Transient Simulations require: Initial Conditions Storage Coefficient Time step

Specific storage: S s = S/b S is storativity or specific yield General 3D equation Heterogeneous, anisotropic, transient, sink/source term

Types of Initial Conditions Static steady state Dynamic steady state Dynamic cyclic conditions (Time distant conditions)

Problem set 5: part 7.3b Generating cyclic steady state conditions

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.)

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, S s

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 doesn’t always work and may give incorrect solutions. Use with caution, or not at all.)

Rule of thumb: take at least five time steps per stress period. 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. MODFLOW divides time into Stress Periods. There are multiple time steps in a stress period. Initial  t

Selecting the time step Can use:  t = Sa 2 /4T for the initial time step of a stress period or find an appropriate time step by trial and error.