TRIM/UnTRIM

TRIM/UnTRIM (Tidal, Residual, and Intertidal Mudflat/Unstructured)

Criterion	Explanation
General Description	TRIM and UnTRIM models are a series of numerical models developed by Prof. Vincenzo Casulli of Trento University. TRIM stands for Tidal, Residual, Intertidal Mudflat Model, which was named in the paper by Cheng, Casulli, and Gartner, 1993. Further implementations and applications of TRIM models in studies of the San Francisco Bay and the Delta took place at the U. S. Geological Survey and at Stanford University. An unstructured grid version of TRIM model family is called UnTRIM which preserves the same basic numerical properties and modeling philosophy, only the computations are carried out over an unstructured orthogonal grid.
Model Domain	The UnTRIM Bay–Delta model was the first 3-D model applied to the Bay–Delta system that spanned the entire estuary from the Pacific Ocean through the Sacramento River and the San Joaquin River.
Developer	Prof. Vincenzo Casulli of Trento University, Italy
Hardware computing requirements	None specified.
Code language	FORTRAN
Original application	San Francisco Bay
Public/proprietary and cost	The model is proprietary and not available to the public.
Physically or empirically based	Physically based
Mathematical methods used	TRIM is a semi-implicit finite difference (volume) model based on the three-dimensional shallow water equations as well as on the three-dimensional transport equation for salt, heat, dissolved matter and suspended sediments. unTRIM is the unstructured grid version of TRIM.
Input data requirements	The TRIM/unTRIM model is well parameterized for the Bay-Delta. Input data includes: Domain (grid parameters, bathymetry) Initial conditions (water level, salinity, water temperature, pollutant and sediment concentrations) Boundary conditions (inflows, outflows, water level, salinity, water temperature, pollutant and sediment concentrations) Physical parameters (describing constants, viscosity, heat flux, sediment, tidal forces) Environmental parameters (precipitation, evaporation, wind speed and direction)
Outputs	Model output includes water level elevation at the free surface, current velocity, tracer concentration (e.g. salinity, temperature, suspended sediments), hydrodynamic pressure.
Pre-processing and post-processing tools	Unknown.
Representation of uncertainty	Uncertainty analysis is not integrated into the modeling framework.
Prevalence	There are many applications of unTRIM to the Bay-Delta in the peer reviewed literature. Other hydrodynamic models, such as RMA 3D, are based on the unTRIM computational engine.
Ease of use for public entities	Because the model is proprietary and not available to the public, it can only be used by the model developers and their consultants.
Ease of obtaining information and availability of technical support	The model is not supported for public use.
Source code availability	The model is proprietary.
Status of model development	The model continues to be used for Bay Delta applications but is only available for use by the model developer and their consultants. Anchor QEA is the primary U.S. consultant using UNTRIM for Bay-Delta applications.
Challenges in integration	Because the model is proprietary and not available to the public, it can only be used by the model developers and their consultants.

References

Andrews, S.W., Gross, E.S. and Hutton, P.H., 2017. Modeling salt intrusion in the San Francisco Estuary prior to anthropogenic influence. Continental Shelf Research, 146, pp.58-81. https://doi.org/10.1016/j.csr.2017.07.010

Casulli, V. and Walters, R.A., 2000. An unstructured grid, three‐dimensional model based on the shallow water equations. International journal for numerical methods in fluids, 32(3), pp.331-348. https://doi.org/10.1002/(SICI)1097-0363(20000215)32:3<331::AID-FLD941>3.0.CO;2-C

Cheng, R.T., Casulli, V. and Gartner, J.W., 1993. Tidal, residual, intertidal mudflat (TRIM) model and its applications to San Francisco Bay, California. Estuarine, Coastal and Shelf Science, 36(3), pp.235-280. https://doi.org/10.1006/ecss.1993.1016

Cheng, R.T. and Casulli, V., 2002. Evaluation of the UnTRIM model for 3-D tidal circulation. In Estuarine and Coastal Modeling (2001) (pp. 628-642).

Gross, E.S., MacWilliams, M.L. and Kimmerer, W.J., 2009. Three-dimensional modeling of tidal hydrodynamics in the San Francisco Estuary. San Francisco Estuary and Watershed Science, 7(2). https://escholarship.org/uc/item/9rv243mg

MacWilliams, M.L., Gross, E.S., DeGeorge, J.F. and Rachiele, R.R., 2007. Three-dimensional hydrodynamic modeling of the San Francisco Estuary on an unstructured grid. Proceedings of International Association of Hydraulic Engineering and Research, Venice, Italy.

MacWilliams, M.L., Bever, A.J., Gross, E.S., Ketefian, G.S. and Kimmerer, W.J., 2015. Three-dimensional modeling of hydrodynamics and salinity in the San Francisco estuary: An evaluation of model accuracy, X2, and the low–salinity zone. San Francisco Estuary and Watershed Science, 13(1). http://dx.doi.org/10.15447/sfews.2015v13iss1art2

MacWilliams, M., Bever, A.J. and Foresman, E., 2016. 3-D Simulations of the San Francisco estuary with subgrid bathymetry to explore long-term trends in salinity distribution and fish abundance. San Francisco Estuary and Watershed Science, 14(2). http://dx.doi.org/10.15447/sfews.2016v14iss2art3