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SEAWAT > SEAWAT 2000 (Superseded) >SEAWAT 2000 Summary

Notice: This USGS product has been superseded by a newer product. USGS no longer updates this page, but it may be useful as a reference or resource.

SEAWAT-2000: Three-dimensional variable-density ground-water flow model

By Christian D. Langevin (U.S. Geological Survey, Fort Lauderdale, Florida),
W. Barclay Shoemaker (U.S. Geological Survey, Fort Lauderdale, Florida), and
Weixing Guo (CDM Missimer, Fort Myers, Florida)

Summary of SEAWAT-2000


SEAWAT-2000 is the latest release of the SEAWAT computer program for simulation of three-dimensional, variable-density, transient groundwater flow in porous media. SEAWAT-2000 was designed by combining a modified version of MODFLOW-2000 and MT3DMS into a single computer program. The code was developed using the MODFLOW-2000 concept of a process, which is defined as "part of the code that solves a fundamental equation by a specified numerical method." SEAWAT-2000 contains all of the processes distributed with MODFLOW-2000 and also includes the Variable- Density Flow Process (as an alternative to the constant-density Ground-Water Flow Process) and the Integrated MT3DMS Transport Process. Processes may be active or inactive, depending on simulation objectives; however, not all processes are compatible. For example, the Sensitivity and Parameter Estimation Processes are not compatible with the Variable-Density Flow and Integrated MT3DMS Transport Processes. The SEAWAT-2000 computer code was tested with the common variable- density benchmark problems and also with problems representing evaporation from a salt lake and rotation of immiscible fluids.


The variable-density groundwater flow equation is solved using a finite-difference approximation similar to the one solved by MODFLOW-2000. The solute-transport equation is solved using one of the approaches available with MT3DMS.


SEAWAT-2000 Version 3.13.00 2006/04/21 - This version of SEAWAT was updated with MODFLOW Version 1.16.00. Additionally, ETS and DRT are now compatible with the VDF proces

SEAWAT-2000 Version 3.12.00 2006/03/14 - This version of SEAWAT was updated with MT3DMS Version 5.10, which includes a new zero-order growth/decay option within the reactions package. This option may be useful for simulating groundwater age as a separate species.

SEAWAT-2000 Version 3.11.02 2005/09/23 - This version of SEAWAT contains a fix for a minor bug that may have caused some transport timesteps to be too short.

SEAWAT-2000 Version 3.11.01 2005/07/25 - This version of SEAWAT contains a bug fix for head-dependent flux calculations for some boundary types.

SEAWAT-2000 Version 3.11.00 2005/04/29 - Added MODFLOW-2000 Version 1.15.00 and MT3DMS Version 5.00. Also added compatability between MNW wells and the VDF Process for freshwater parts of a model domain.

SEAWAT-2000 Version 3.10.01 2004/03/30 - This version of SEAWAT contains bug fixes for three coding errors: (1) In the previous version, the value for HDRY was not always written to the output head file if a cell went dry during the simulation. (2) A runtime error was encountered in certain instances when the IMT Process was used with the GWF Process (instead of the VDF Process). (3) If MODFLOW timesteps were shorter than the calculated transport timestep, the density array was not updated properly.

SEAWAT-2000 Version 3.10 2004/02/13 - This version of SEAWAT contains substantial improvements over previous releases. The program is now based on MODFLOW-2000 (Version 1.12.01) and MT3DMS (Version 4.500), and uses the concept of a process. Details of SEAWAT-2000 are described in U.S. Geological Survey Open-File Report 03-426.

SEAWAT Version 2.12 2002/09/13 - Fixed problem with calculation of EVT fluid density. Thanks to Adam Taylor and Barclay Shoemaker. Also fixed bug in calculation of default riverbed thickness. Thanks to Lou Motz and Nebiyu Tiruneh from the University of Florida for locating this problem.

SEAWAT Version 2.11 2002/08/09 - Fixed bug that caused program to bomb for certain problems involving wetting and drying. Thanks to Trayle Kulshan and Steve Gorelick from Stanford University for help in locating this problem.

SEAWAT Version 2.10 2002/02/07 - Code consists of MODFLOW-88 and MT3DMS Version 3.50.A. Upgraded the CFACE subroutine with the improved CFACE subroutine from MT3DMS Version 4.00. Reformulated flow equation to conserve fluid mass. Redesigned boundary conditions to represent variable-density flow. Added an iterative method for coupling flow and transport. Program redesigned as double precision.

SEAWAT Version 1.1 1998/05/01 - Initially released by Weixing Guo (Missimer International, Inc.) and Gordon D. Bennett (S.S. Papadopulos & Associates, Inc.)

Data Requirements

In order to use SEAWAT, initial conditions, hydraulic properties, and stresses must be specified for every model cell in the finite-difference grid.

Output Options

Primary output is head and concentration, which can be written to the listing file or to separate binary files. Other output includes the complete listing of all input data, drawdown, flow budget, and transport budget data. Flow budget data are printed as a summary in the listing file, and detailed budget data for all model cells can be written into a separate file. All binary output is written to files that are opened with the FORM='BINARY' option. This means that some pre- and post-processors may not be able to read the output unless the open statements are modified, the program is recompiled, and the model is rerun.

System Requirements

SEAWAT is written in Fortran 77 with the following extensions: use of variable names longer than 6 characters, Fortran 90 statements for dynamic memory allocation, a call to SUBROUTINE GETARG to retrieve command-line arguments, and two calls to DATE_AND_TIME, which is a Fortran 90 intrinsic subroutine. Generally, the program is easily installed on most computer systems. The code has been used on DOS-based 386 or greater computers having a math coprocessor and 4 mb of memory.


GLO1 -- Global Process
GWF1 -- Ground-Water Flow Process
VDF1 -- Variable-Density Flow Process
OBS1 -- Observation Process
SEN1 -- Sensitivity Process
PES1 -- Parameter-Estimation Process
IMT1 -- Integrated MT3DMS Process

Process compatibility issues are described in the user's manual. In general, the VDF and IMT Processes are not compatible with SEN and PES, and are only slightly compatible with OBS. VDF is an alternative to GWF, and thus the two cannot be used concurrently in a simulation.

Packages Compatible with the Variable-Density Flow (VDF) Process

BAS6 -- Basic
BCF6 -- Block-Centered Flow
LPF -- Layer Property Flow
HUF2 -- Hydrogeologic Unit Flow. Note that VDF is not yet compatible with the Layer Variable-Direction Horizontal Anisotropy (LVDA) capability. The LVDA capability should not be used with the VDF process. The VDF process is compatible with the three features described in Open-File Report 03-347.
HFB6 -- Hydraulic Flow Barrier
DRN -- Drain
RIV -- River
GHB -- General-Head Boundary
EVT -- Evapotranspiration
WEL -- Well
RCH -- Recharge
CHD -- Time-Variant Constant Head
FHB -- Flow and Head Boundary
MNW -- Multi-Node Well
DRT -- Drains with Return Flow
ETS -- Evapotranspiration with a Segmented Function
SIP -- Strongly Implicit Procedure
SOR -- Slice-Successive Overrelaxation
PCG -- Preconditioned Conjugate Gradient Solver (also called PCG2)
DE4 -- Direct Solver
GMG -- Geometric Multi-Grid Solver
OC -- Output Control Option
LMT6 -- Linkage with MT3DMS
BTN -- Basic Transport
ADV -- Advection
DSP -- Dispersion
SSM -- Source/Sink Mixing
RCT -- Reaction
GCG -- Generalized Conjugate Gradient Solver
TOB -- Transport Observations
OBS -- Observation
HOB -- Hydraulic-Head Observation
GHOB -- General-Head Boundary Observation
DROB -- Drain Observation
DTOB -- Drain with Return Flow Observation
RVOB -- River Observation
CHOB -- Constant-Head Flow Observation

Other packages (distributed with MODFLOW-2000) are included in SEAWAT-2000, however, these additional packages may not be compatible with the VDF Process.


The basic documentation is contained in the following two reports:

Langevin, C.D., Shoemaker, W.B., and Guo, W., 2003, MODFLOW-2000, the U.S. Geological Survey Modular Ground-Water Model--Documentation of the SEAWAT-2000 Version with the Variable-Density Flow Process (VDF) and the Integrated MT3DMS Transport Process (IMT): U.S. Geological Survey Open-File Report 03-426, 43 p.

Guo, W., and Langevin, C.D., User's guide to SEAWAT: A computer program for simulation of three-dimensional variable-density ground-water flow: Techniques of Water-Resources Investigations of the U.S. Geological Survey, Book 6, Chapter A7, 77 p.

Users will also need documentation for MODFLOW-2000 and MT3DMS, and possibly the references cited in those reports.



Christian Langevin
U.S. Geological Survey
3110 SW 9th Avenue
Fort Lauderdale, FL 33315

Barclay Shoemaker
U.S. Geological Survey
3110 SW 9th Avenue
Fort Lauderdale, FL 33315

Weixing Guo
CDM Missimer
8140 College Parkway, Suite 202
Fort Myers, Florida

See for information on ordering printed copies of USGS publications.


This program is public domain and is released on the condition that neither the U.S Geological Survey nor the United States Government may be held liable for any damages resulting from their authorized or unauthorized use. See also User Rights.

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