NAMEmoc - Two-dimensional method-of-characteristics ground-water flow and transport modelABSTRACTThis model simulates solute transport in flowing ground water. It is applicable to one- or two-dimensional problems involving steady- state or transient flow. The model computes changes in concentration over time caused by the processes of advective transport, hydrodynamic dispersion, mixing or dilution from fluid sources, and certain types of chemical reactions (first-order irreversible-rate reaction or equilibrium-controlled sorption- desorption and ion exchange). Gradients of fluid density, viscosity, and temperature are assumed not to affect the velocity distribution. However, the aquifer may be heterogeneous and anisotropic. It is one of the most used models for solute-transport problems. Complete documentation of the current version of this model requires both the report by Konikow and Bredehoeft (1978) and the report by Goode and Konikow (1989).METHODThe model couples the ground-water flow equation with the solute- transport equation. The digital computer program uses an iterative alternating-direction implicit procedure to solve a finite- difference approximation to the ground-water flow equation (alternative modules to solve the flow equation using SIP or using a direct solver based on D4 ordering are also available). The model uses the method of characteristics to solve the solute-transport equation. This incorporates a particle-tracking procedure to represent advective transport and a two-step explicit finite- difference procedure to solve equations that describe the effects of hydrodynamic dispersion and fluid sources. This explicit procedure has several stability criteria associated with it, but the consequent time-step limitations are automatically determined by the program.HISTORYVersion 3.2.2 1996/01/22 - In separate velocity output file, change in code to write Vy assuming y-axis increases upward Version 3.2 1995/03/21 - Minor bug fixes and improvements Version 3.1 1994/07/06 - WRDAPP tape 2.1 update release with minor bug fixesDATA REQUIREMENTSInitial conditions, boundary conditions, aquifer properties at every node, and grid descriptors. PLEASE NOTE: there is a typographical error on page 16 of the 1994 documentation (WRIR 94-4115) regarding the input format for the NODEID matrix. The correct format is (20I1) instead of (40I1).OUTPUT OPTIONSSee documentation.SYSTEM REQUIREMENTSMOC is written in Fortran 77 with the following extensions: use of variable names longer than 6 characters and use of the $ format descriptor. Generally, the program is easily installed on most computer systems. The code has been used on UNIX-based computers and DOS-based 386 or greater computers having a math coprocessor and 4 mb of memory.DOCUMENTATIONKonikow, L.F., Granato, G.E., and Hornberger, G.Z., 1994, User's guide to revised method-of-characteristics solute-transport model (MOC--Version 3.1): U.S. Geological Survey Water-Resources Investigations Report 94-4115, 63 p.REFERENCESGoode, D.J., and Konikow, L.F., 1989, Modification of a method-of- characteristics solute-transport model to incorporate decay and equilibrium-controlled sorption or ion exchange: U.S. Geological Survey Water-Resources Investigations Report 89-4030, 65 p. Konikow, L.F., and Bredehoeft, J.D., 1978, Computer model of two- dimensional solute transport and dispersion in ground water: U.S. Geological Survey Techniques of Water-Resources Investigations, book 7, chap. C2, 90 p.TRAININGModeling Transport of Ground-Water Solutes (GW2080TC), offered annually at the USGS National Training Center.CONTACTSOperation and Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 h2osoft@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). The WWW page and anonymous FTP directory from which the MOC software can be retrieved are, respectively: http://water.usgs.gov/software/moc.html --and-- /pub/software/ground_water/moc See http://water.usgs.gov/software/ordering_documentation.html for information on ordering printed copies of USGS publications.SEE ALSOmodflow(1) - Modular three-dimensional ground-water flow model Modflowp(1) - Parameter-estimation version of the modular model premoc - A preprocessor for the two-dimensional method of characteristics (MOC) solute-transport model (version 4.1.2) sutra(1) - Saturated and (or) unsaturated, constant or variable-density fluid flow, and solute or energy transport (2-dimensional finite-element code) vs2di(1) - A graphical software package for simulating fluid flow and solute or energy transport in variably saturated porous media

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