Boundary Conditions - Boundary conditions must be de-
fined for solution of the simultaneous finite differ-
ence equations. An initial or prior value of the head
at each node is defined as either a somewhat arbitrary
set of values at the beginning of the simulation or
the heads from the immediately preceding timestep.
The other set of boundary conditions required imply a
known condition at the edge of the study area. These
may be either "no-flow" (barrier) nodes or "constant-
head" (recharge) nodes.    Barrier boundaries are im-
posed by assigning a very low hydraulic conductivity
(10-25) at these nodes..   Recharge boundaries are im-
posed by assigning a very high storage coefficient
(such as 1025) at these nodes.   It should be realized
that the edges of the finite difference grid represent
barrier boundaries and effectively constitute a de-
fault condition if no boundary is explicitly set.

Golder Associates

March, 1982

-16-

786085