Implicit Approximation
Implicit approximation can be solved using: Point iteration (G/S, SOR) Direct (matrix) solution Combination of matrix soln and iteration
Examples of solution techniques that combine matrix solution with iteration: IADI (see chapter 5 of W&A) SSOR* SIP* PCG2* *Used in MODFLOW
General 3D equation used in MODFLOW i-1 i i+1 Block centered grid xixi x i-1/2 x i+1/2
K values in the space between nodes is calculated using the harmonic mean
The default boundary condition is no flow.
Types of Layers (LAYCON array) Confined Unconfined Convertible (Useful to think in terms of a layer transmissivity.)
Conductance