U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3047

September 2009

SEAWAT: A Computer Program for Simulation of Variable-Density 

Groundwater Flow and Multi-Species Solute and Heat Transport

Printed on recycled paper

Selected SEAWAT Applications 

With the increase in demand for fresh groundwater resources, the 

number of studies that require explicit representation of fluid density 

variation has increased. Although many of these studies focus on 

saltwater intrusion issues in coastal areas, dense saline brines can also 

threaten freshwater resources in continental aquifers. USGS investigators have developed expertise in applying the SEAWAT computer 

program to a wide variety of groundwater problems. The following 

list demonstrates the breadth of these investigations, and provides 

examples of the types of hydrologic issues that have been addressed.

Saltwater Intrusion and Upconing

□ Upconing was identified to be a greater threat near Bonita Springs, 

Florida, than lateral saltwater intrusion (Shoemaker and others, 

2003).

□ The effects of groundwater pumping and sea-level rise on the 

freshwater-saltwater interface were simulated as part of a study of 

freshwater availability on Cape Cod, Massachusetts (Masterson, 

2004; Masterson and Garabedian, 2007).

□ The relative importance of drought, well-field pumping, sea-level 

rise, and canal management on saltwater intrusion were evaluated for the Biscayne aquifer in southern Florida (Dausman and 

Langevin, 2005).

□ Saltwater intrusion patterns were simulated for the Coastal Plain 

aquifer system of Virginia (Heywood and Pope, 2009).

□ Areas susceptible to saltwater intrusion were identified for the 

Eastern Shore of Virginia (Sanford and others, 2009). 

□ Aquifer salinization rates and thermal plume migration were simulated for an extensive hypersaline cooling canal system in southern 

Florida (Huges and others, 2009).

Submarine Groundwater Discharge

□ The rate of fresh groundwater discharge into Biscayne Bay was 

estimated to be about 10 percent of the measured surface-water 

discharge (Langevin, 2001; 2003).

□ A SEAWAT model was developed to help guide data collection 

efforts for submarine groundwater discharge studies (Dausman and 

others, 2007).

Coastal Wetland Hydrology

□ FTLOADDS, a program that combines SEAWAT with a twodimensional hydrodynamic surface-water model, was applied to the 

southern Everglades of Florida (Langevin and others, 2005).

□ Water-management strategies were optimized using a FTLOADDS 

model (Swain and James, 2007). 

SEAWAT Design and Strengths

The SEAWAT design is based on the concept of combining two 

well-established and proven groundwater programs, MODFLOW 

and MT3DMS, into a single program that simulates variable-density 

groundwater flow and transport. This design concept leverages the substantial capabilities of MODFLOW and MT3DMS, and extends those 

capabilities to coastal aquifers and other environments where density 

variations are important. For example, MT3DMS has an option to 

simulate zero-order decay and growth, which can be used for groundwater age simulations. This functionality is also available in SEAWAT, 

making it possible to simulate groundwater age for variable-density 

problems. The SEAWAT design concept has the following associated 

strengths:

□ Accuracy—The program builds on the thoroughly tested MODFLOW 

and MT3DMS methods for solving groundwater flow and transport, 

respectively. Variable-density functionality is tested with most benchmark problems.

□ Computational Efficiency—SEAWAT includes standard MODFLOW 

solvers for flow and flexible MT3DMS methods for solving transport. 

The modular structure allows capabilities to be activated as needed.

□ Familiarity—Users familiar with the constant-density versions 

of MODFLOW and MT3DMS can transition to variable-density 

simulations with few difficulties. Furthermore, the program can be 

used with existing groundwater software pre- and post-processors, 

as well as other MODFLOW-related programs (MODPATH, 

ZONEBUDGET, Modelviewer, and so forth).

□ Modularity—The SEAWAT program design makes it easy to modify 

or add new processes and packages.

□ Support—SEAWAT is actively maintained and developed to include 

new features and capabilities and to support new MODFLOW and 

MT3DMS packages and processes.
□ A FTLOADDS model was used to evaluate the hydrologic effects of 

Everglades restoration (Wang and others, 2007). 

Deep-Well Injection

□ Upward migration of injected treated effluent was simulated for a 

wastewater-treatment plant in Florida (Dausman and others, in press).

Brine Transport

□ A dense brine pool near Syracuse, New York, was determined to have 

migrated to its present position from a distant salt source (Yager and 

others, 2007).

□ Upward brine migration through a collapse feature was simulated 

for a flooded salt mine in Livingston County, New York (Yager and 

others, 2009).

SEAWAT Version 4

Since its first release by the USGS in 2002, SEAWAT has continued to evolve by supporting additional MODFLOW and MT3DMS 

packages and by adding new functionality. The most recent SEAWAT 

revision, Version 4, contains new features that allow users to simulate 

multi-species solute and heat transport (Langevin and others, 2007). 

One of the benefits of these added capabilities is that temperature 

effects on fluid density and viscosity can be simulated. Dausman and 

others (2009) demonstrate the use of SEAWAT Version 4 by simulating 

a set of complex variable-density benchmark problems. Langevin and 

others (2009) test the simultaneous solute and heat transport capabilities by simulating a laboratory experiment involving warm freshwater 

flowing over cold saltwater (fig. 1).

Dausman, A.M., Langevin, C.D., Thorne, D., and Sukop, M.C., 2009, Application of SEAWAT to select variable-density and viscosity problems: U.S. 

Geological Survey Scientific Investigations Report 2009-5028, 33 p. 

Heywood, C.E., and Pope, J.P., 2009, Simulation of ground-water flow in 

the Coastal Plain aquifer system of Virginia: U.S. Geological Survey 

Scientific Investigations Report 2009-5039, 115 p.

Hughes, J.D., Langevin, C.D., and Brakefield-Goswami, L., 2009, Effect 

of hypersaline cooling canals on aquifer salinization: Hydrogeology 

Journal, published online August 12, 2009: DOI 10.1007/s10040-009-

0502-7.

Langevin, C.D., 2001, Simulation of ground-water discharge to Biscayne 

Bay, Southeastern Florida: U.S. Geological Survey Water-Resources 

Investigations Report 00-4251, 127 p.

Langevin, C.D., 2003, Simulation of submarine ground water discharge 

to a marine estuary, Biscayne Bay, Florida: Ground Water, v. 41, no. 6, 

p. 758-771.

Langevin, C.D., Dausman, A.M., and Sukop, M.C., 2009, Solute and heat 

transport model of the Henry and Hilleke Laboratory Experiment: 

Ground Water, published online June 29, 2009: DOI 10.1111/j.1745-

6584.2009.00596.x.

Langevin, C.D., Swain, E.D., and Wolfert, M.A., 2005, Simulation of integrated surface-water/ground-water flow and salinity for a coastal wetland 

and adjacent estuary: Journal of Hydrology, v. 314, no. 1-4, p. 212-234.

Langevin, C.D., Thorne, D.T., Jr., Dausman, A.M., Sukop, M.C., and Guo, 

Weixing, 2007, SEAWAT Version 4: A computer program for simulation of multi-species solute and heat transport: U.S. Geological Survey 

Techniques and Methods, book 6, chap. A22, 39 p.

Masterson, J.P., 2004, Simulated interaction between freshwater and saltwater and effects of ground-water pumping and sea-level change, Lower 

Cape Cod aquifer system, Massachusetts: U.S. Geological Survey Scientific Investigations Report 2004-5014, 78 p.

Masterson, J.P., and Garabedian, S.P., 2007, Effects of sea-level rise on 

ground-water flow in a coastal aquifer system: Ground Water, v. 45, no. 2, 

p. 209-217.

Sanford, W.E., Pope, J.P., and Nelms, D.L., 2009, Simulation of groundwater-level and salinity changes in the Eastern Shore, Virginia: U.S. 

Geological Survey Scientific Investigations Report 2009-5066, 126 p.

Shoemaker, W.B., and Edwards, K.M., 2003, Potential for saltwater intrusion into the lower Tamiami aquifer near Bonita Springs, southwestern 

Florida: U.S. Geological Survey Water-Resources Investigations Report 

03-4262, 74 p.

Swain, E.D., and James, D.E., 2007, Inverse modeling of surface-water discharge to achieve restoration salinity performance measures in Florida 

Bay, Florida: Journal of Hydrology, v. 351, p. 188-202.

Wang, J.D., Swain, E.D., Wolfert, M.A., Langevin, C.D., James, D.E., and 

Telis, P.A., 2007, Application of FTLOADDS to simulate flow, salinity, 

and surface-water stage in the Southern Everglades, Florida: U.S. Geological Survey Scientific Investigations Report 2007–5010, 112 p.

Yager, R.M., Kappel, W.M., and Plummer, L.N., 2007, Origin of halite 

brine in the Onondaga Trough near Syracuse, New York State, USA: 

Modeling geochemistry and variable-density flow: Hydrogeology 

Journal v. 15, no. 7, p. 1321-1339.

Yager, R.M., Misut, P.E., Langevin, C.D., and Parkhurst, D.L., 2009, Brine 

migration from a flooded salt mine in the Genesee Valley, Livingston 

County, New York: Geochemical modeling and simulation of variabledensity flow: U.S. Geological Survey Professional Paper 1767, 59 p.

Author—Christian D. Langevin

References Cited

Dausman, A.M., Doherty, J., Langevin, C.D., Dixon, J., (in press), Hypothesis testing of buoyant plume migration using a highly parameterized 

variable-density groundwater model at a site in Florida, USA: Hydrogeology Journal, accepted August 1, 2009: DOI 10.1007/s10040-009-

0511-6.

Dausman, A.M., and Langevin, C.D, 2005, Movement of the saltwater interface in the surficial aquifer system in response to hydrologic stresses and 

water-management practices, Broward County, Florida: U.S. Geological 

Survey Scientific Investigations Report 2004-5256, 81 p.

Dausman, A.M., Langevin, C.D., and Sukop, M.C., 2007, Simulation of submarine groundwater discharge salinity and temperature variations: Implications for remote detection, in Sanford, W., Langevin, C.D., Polemio, 

M., and Povinec. P., eds., 2007, A new focus on groundwater-seawater 

interactions: Oxfordshire, U.K., IAHS Publication 312, p. 272-280. SALINITY, IN GRAMS PER LITER TEMPERATURE, IN DEGREES CELSIUS

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MODPATH FLOW LINE

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Figure 1. Results from a simultaneous solute and heat transport 

simulation (Langevin and others, 2009).

For additional information:

Christian D. Langevin

U.S. Geological Survey

3110 SW 9th Avenue

Fort Lauderdale, Florida 33315

langevin@usgs.gov

SEAWAT: http://water.usgs.gov/ogw/seawat

MODFLOW: http://water.usgs.gov/nrp/gwsoftware/

modflow.html

MT3DMS: http://hydro.geo.ua.edu/mt3d/