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Groundwater Modeling

Boundary Conditions

•    Boundary Conditions of the First Kind (Dirichlet Condition)

Known pressure (velocity potential or total heard) head, e.g. constant or varying in time or space.

Since total head, h, is known, an eąuation for head is not needed along the boundary.

•    Boundary conditions of the Second Kind (Neumann Condition)

Known flux or specific discharge (mass per unit volume per unit time.

Express in terms of flux exiting a boundary celi.

For a no flow boundary, 5<|)/dn = 0.

•    Boundary conditions of the Third Kind (mixed Boundary condition or Cauchy Condition)

Flux normal to a boundary can be expressed in terms of the head along the boundary and a known constant.

•    Phreatic surface with accretion

The pressure is equal to atmospheric and it is necessary to know the flux.

The phreatic surface can vary if enough information on the aquifer properties are known. Can be an unconfined or confined aquifer.

•    Surface of seepage

Pressure is equal to zero so the velocity potential is a function of elevation.

•    Boundary Between Two Porous Media

The pressure or total head is equal along the boundary.

Continuity must be assured along the boundary.

•    For MODFLOW, use constant-head, inactive or variable head cells.

Groundwater Modeling