SUNTANS (Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier-Stokes Simulator)

Criterion	Explanation
General Description	SUNTANS is an open-source 3-D circulation model developed at Stanford University that computes flows on an unstructured grid using a finite-volume method. SUNTANS is highly parallelized and designed to be used on large parallel computing clusters. SUNTANS is similar to the 3-D unstructured-grid UnTRIM model. It includes algorithms for sediment transport and surface wave effects on bottom stresses and flows. Various grids have been created for parts and the entirety of the Bay–Delta in the context of applications to the South Bay Salt Pond restoration as well as for detailed flow modeling in the Delta.
Model Domain	The model domain is flexible and can be specified by the user, and can include coastal, estuarine, lakes and river areas.
Developer	Stanford University
Hardware computing requirements	SUNTANS is highly parallelized and designed to be used on large parallel computing clusters.
Code language	C
Original application	SUNTANS is an unstructured-grid tool that adaptively simulates multiscale physics in the coastal ocean; specifically designed for coastal and estuarine processes. Early applications were to the San Francisco bay and Snohomish River estuary.
Public/proprietary and cost	The model source code is open source.
Physically or empirically based	Physically based
Mathematical methods used	SUNTANS computes flows on an unstructured grid using a finite-volume method, and implements two key approaches: (1) a semi-implicit free surface; and (2) a fractional step method to efficiently calculate the effects of nonhydrostatic pressures.
Input data requirements	Model developers recommend the grid generation package GAMBIT from Fluent, Inc. All input files are ASCII text files. Input data includes: Domain (grid parameters, bathymetry) Initial conditions (water level, salinity, water temperature, water velocity) Boundary conditions (inflows, outflows, water level, salinity, water temperature) Physical parameters (describing constants, viscosity, heat flux, sediment, tidal forces) Environmental parameters (wind speed and direction)
Outputs	A standalone GUI is provided to view results (but cannot output results to standard figure file formats). Model outputs are provided in ASCII or binary files. Model output includes: free surface, velocity vectors, salinity, temperature, nonhydrostatic pressure, eddy viscosity, scalar diffusivity, water depth.
Pre-processing and post-processing tools	Model developers recommend the grid generation package GAMBIT from Fluent, Inc. A standalone GUI is provided to view results (but cannot output results to standard figure file formats).
Representation of uncertainty	Uncertainty is not represented.
Prevalence	The model is used by the academic community, therefore most or all known applications are in the peer-reviewed literature.
Ease of use for public entities	SUNTANS is highly parallelized and designed to be used on large parallel computing clusters, therefore the barrier is high for widespread public use.
Ease of obtaining information and availability of technical support	The model is maintained on Github which acts as a user forum; there is no formal help desk. The Github repository does not have an active user base.
Source code availability	The model source code is open source.
Status of model development	The model is available for immediate use. The following features were recently implemented in SUNTANS: a suspended sediment transport model and a spectral wave model to include the effects of wave-driven currents and bottom stresses. The following features are under development: simulation of flows in salt-marsh estuaries with a marsh vegetation drag module along with a culvert module; and the method of subgrid bathymetry, whereby bathymetry data at a resolution that is finer than the mesh are incorporated into the solution without increasing the resolution of the underlying computational mesh.
Challenges in integration	Although the model is open source, it is designed as a research tool and is not well documented for public use. The model is highly parallelized and designed to be used on large parallel computing clusters, therefore the barrier is high for widespread public use.

References

Y.J. Chou, K.S. Nelson, R.C. Holleman, O.B. Fringer, M.T. Stacey, J.R. Lacy, S.G. Monismith, and J.R. Koseff, 2018, "Three-dimensional modeling of fine sediment transport by waves and currents in a shallow estuary", J. Geophys. Res.-Oceans., 123, https://doi.org/10.1029/2017JC013064

Hsu K., Stacey M.T., Holleman R.C., 2013, "Exchange between an estuary and an intertidal marsh and slough", Estuaries Coasts 36:1137–1149. doi: http://dx.doi.org/10.1007/s12237-013-9631-2

Wolfram P.J., Fringer .O.B, Monsen N., Gleichauf K., Fong D., Monismith S.G., 2016, "Modeling intrajunction dispersion at a well-mixed tidal river junction", Hydraul Eng 42(8). doi: http://dx.doi.org/10.1061/(ASCE)HY.1943-7900.0001108

Stacey, M., Holleman, R., and Gross, E.S., 2011, "Test Applications of High Resolution 3- Dimensional Hydrodynamic Model (SUNTANS) to San Francisco Bay", Contribution No. 638. San Francisco Estuary Institute, Oakland, California. Available at: https://www.sfei.org/documents/test-application-high-resolution-3-dimensional-hydrodynamic-model-suntans-san-francisco

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