** SWMS_2D is a computer
program for simulating water and solute movement in two-dimensional variably
saturated media. The program numerically solves the Richards' equation for saturated-unsaturated
water flow and the convection-dispersion equation for solute transport. The
flow equation incorporates a sink term to account for water uptake by plant
roots. The transport equation includes provisions for linear equilibrium adsorption,
zero-order production, and first-order degradation. The program may be used
to analyze water and solute movement in unsaturated, partially saturated, or
fully saturated porous media. **

**SWMS_2D can handle flow
regions delineated by irregular boundaries. The flow region itself may be composed
of nonuniform soils having an arbitrary degree of local anisotropy. Flow and
transport can occur in the vertical plane, the horizontal plane, or in a three-dimensional
region exhibiting radial symmetry about the vertical axis. The water flow part
of the model can deal with prescribed head and flux boundaries, as well as boundaries
controlled by atmospheric conditions.**

**The governing flow and
transport equations are solved numerically using Galerkin-type linear finite
element schemes. Depending upon the size of the problem, the matrix equations
resulting from discretization of the governing equation are solved using either
Gaussian elimination for banded matrices, or a conjugate gradient method for
symmetric matrices and the ORTHOMIN method for asymmetric matrices. The program
is written in ANSI standard FORTRAN 77. Computer memory is a function of the
problem definition. This report serves as both a user manual and reference document.
The program comes with a manual containing instructions for data input preparation.
Example input and selected output files are also provided as is a listing of
the source code. **