SUTRA (Saturated-Unsaturated TRAnsport)

Criterion	Explanation
General Description	A finite element simulation model for saturated-unsaturated fluid density-dependent groundwater flow with energy transport or chemically-reactive single species transport.
Model Domain	Subsurface saturated and unsaturated zones
Developer	U.S. Geological Survey (USGS)
Hardware computing requirements	SUTRA executable code is available for Microsoft Windows
Code language	FORTRAN
Original application	SUTRA is a model for saturated-unsaturated, variable-density ground-water flow with solute or energy transport. The model simulates zeroth- and first-order solute production/decay, and zeroth-order energy production/decay, and represents linear, Freundlich, or Langmuir equilibrium adsorption. The original application was the simulation of coastal solute transport in the 1980s. The user may program unsaturated flow conditions.
Public/proprietary and cost	Public; No cost
Physically or empirically based	Physically based
Mathematical methods used	Simulations may be either two-dimensional or three-dimensional, and can be either steady-state or transient. For discretization, the model uses a hybrid Galerkin-finite-element and integrated-finite-difference method. The finite elements are either quadrilateral (2D) or generalized hexahedral (3D). Th model numerically solves the groundwater flow, the convective-dispersion equation for solute transport and the near flow equation.
Input data requirements	All input data are contained in text files and are grouped into "datasets". The latest version (2.2) allows the user to specify time-dependent boundary conditions without programming in FORTRAN. SutraPrep can be used to create a SUTRA main input file, an initial conditions file, and a 3D plot of the finite-element mesh in Virtual Reality Modelling Language (VRML) format. Required input data include groundwater flow related parameters (boundary conditions and initial conditions, permeability, storativity, etc.). Porosity and unsaturated flow properties are assigned at each model node; permeabilities, longitudinal and transverse dispersivities, and unsaturated flow properties are assigned to each element. Fluid density is a linear function of solute concentration or temperature throughout the model. Fluid viscosity is a function of temperature in energy transport simulations.
Outputs	Output is written to text files and to the screen. Includes optional output files that summarize specifications and computed results at boundary condition nodes. Outputs include pressure, solute concentrations or temperature, fluid velocities at each node and solute, energy and water budgets.
Pre-processing and post-processing tools	The SutraSuite package includes several pre- and post-processing programs designed for use with SUTRA. Post-processing software are Windows-based. These include mesh, contour, and velocity vector plotting, as well as creating and exporting animations and saves visualizations as Bitmaps or VRML plots.
Representation of uncertainty	The model does not have built-in uncertainty representation. This can be assessed for each specific case using sensitivity analysis.
Prevalence	SUTRA is very widely used worldwide for research on seawater intrusion and other variable-density groundwater flow problems based on solute transport or heat transport. Many practical engineering studies invoke SUTRA. SUTRA has been used in the Delta to simulate heat flow and solute loads (Burow et al. 2005)
Ease of use for public entities	Readily available, easy to use
Ease of obtaining information and availability of technical support	Technical support is offered on the USGS site at: https://water.usgs.gov/nrp/gwsoftware/sour/support/support.htm Included are examples of common errors, FAQs, a guide for getting started with SutraSuite, and a glossary of SUTRA terms. For additional help, or to report a bug, contact the author at: aprovost@usgs.gov
Source code availability	The source code is available for download at: https://water.usgs.gov/nrp/gwsoftware/sutra/sutra.html
Status of model development	Fully developed and ready to use
Challenges for integration	The primary challenge would be related to integration with surface water models and in the simulation of evaporation from the shallow water table. The model does not appear to have significant limitations in the Delta. It was used to simulate flow, solute and heat transport on Twitchell island (Burow et al. 2005).

References

See https://water.usgs.gov/nrp/gwsoftware/sutra/sutra.html for a model overview, the source code, documentation, and software download.

Burow K., Constanz J., Fujii R., 2005, Heat as a tracer to estimate organic carbon loads from a restored wetland. Groundwater 43(4):545-556. https://doi.org/10.1111/j.1745-6584.2005.0055.x

Voss, C.I., and Provost, A.M., 2002 (Version of September 22, 2010), SUTRA, A model for saturated-unsaturated variable-density ground-water flow with solute or energy transport, U.S. Geological Survey Water-Resources Investigations Report 02-4231, 291 p.

Voss C.I., 1999, USGS SUTRA Code — History, Practical Use, and Application in Hawaii. In: Bear J., Cheng A.HD., Sorek S., Ouazar D., Herrera I. (eds) Seawater Intrusion in Coastal Aquifers — Concepts, Methods and Practices. Theory and Applications of Transport in Porous Media, vol 14. Springer, Dordrecht.

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