FourPt(1) U.S. Geological Survey (wrdapp) FourPt(1) NAME FourPt - An unsteady, one-dimensional, open-channel flow model ABSTRACT FOURPT is a numerical model for simulating unsteady, one-dimensional flow in networks of open channels. Options particularly useful in training or prototyping include selection of governing equations (kinematic, diffusion, or dynamic), boundary-value perturbation, and user-programmable constraint equations. The model can simulate non- trivial concepts, such as flow in complex interconnected channel networks, meandering channels with variable effective flow lengths, hydraulic structures defined by unique three-parameter relations, and density-driven flow. Channel geometry may be rectangular, trapezoidal, or irregular depending upon which of three channel- property modules is linked with the program. METHOD As implied by the name, FOURPT uses the four-point-implicit solution scheme. Simultaneous equations are solved by Gaussian elimination using an indexed, asymmetric, sparse-matrix solver that is particularly useful in application to large (hundreds of channels), complex networks of interconnected channels. All relations constraining unknown variables, discharge and water-surface elevation, at boundaries and channel junctions are implemented implicitly. The model is coded in Fortran 77, and data encapsulation is used extensively to simplify modification and to encourage the modification and use of FOURPT modules by other programs and programmers. HISTORY FOURPT was originally (1991) written and used primarily as a teaching supplement for a course in one-dimensional streamflow modeling. However, it does have practical utility and has been applied (1993) to the Sacramento-San Joaquin Delta (a complex network of about 500 channels) by the California Department of Water Resources. DATA REQUIREMENTS Input data are grouped according to type, program control, channel properties, network schematic, initial values, boundary values, and constraint parameters. The first three types are necessary for any model execution, and the remainder are optional, either not required or approximated by the model. OUTPUT OPTIONS Level of detail included in the model execution log is user defined. Time series and space series of computed water-surface elevations and flow at locations and times selected by the user are available in separate tab-delimited text files. SYSTEM REQUIREMENTS FOURPT is written in Fortran 77 with the following extensions: use of include files, variable names longer than 6 characters, use of mixed case, and unformatted read of internal file. Memory 7 Jul 1998 1 FourPt(1) U.S. Geological Survey (wrdapp) FourPt(1) requirements depend on array dimensioning parameters in include files. Generally, the program is easily adapted to most computer systems. The code has been used on UNIX-based computers, Macintosh, and DOS-based 386 or greater computers having a math coprocessor and 4 mb of memory. WARNING: FOURPT is coded such that local variables are expected to be static (that is, local variables need to retain their values upon exit of a routine). Thus, the appropriate compiler option(s) must be specified to produce reliable results. APPLICATIONS The model is being applied (1993) to the Sacramento-San Joaquin Delta in California (about 500 interconnected channels) and the Loiza Basin in Puerto Rico (about 25 channels with upland slopes and a reservoir). DOCUMENTATION DeLong, L.L., Thompson, D.B. and Lee, J.K., 1997, The computer program FourPt (Version 95.01)--a model for simulating one- dimensional, unsteady, open-channel flow: U.S. Geological Survey Water-Resources Investigations Report 97-4016, 69 p. REFERENCES DeLong, L.L., 1986, Extension of the unsteady one-dimensional open- channel flow equations for flow simulation in meandering channels with flood plains, in Subitzky, S., ed., selected papers in the hydrologic sciences: U.S. Geological Survey Water-Supply Paper 2290, p. 101-105. DeLong, L.L., 1993, A numerical model for learning concepts of streamflow simulation, in National Conference on Hydrologic Engineering, 1993, Proceedings: American Society of Civil Engineering, p. 1586-1591. DeLong, L.L., Thompson, D.B., and Fulford, J.M., 1992, Data encapsulation using Fortran-77 modules: Fortran Forum, v. 11, no. 3, p. 11-19. ACM. Nader, P., 1993, Application of Four Point model to the Sacramento- San Joaquin Delta, in National Conference on Hydrologic Engineering, 1993, Proceedings: American Society of Civil Engineering, p. 442-447. Thompson, D.B., DeLong, L.L., and Fulford, J.M., 1992, Data encapsulation using Fortran-77 modules - a first step toward object-oriented programming: U.S. Geological Survey Water- Resources Investigations Report 92-4123. TRAINING A user of this model should have a good understanding of basic hydraulics and flow in open channels, as well as a general familiarity with techniques for numerically solving partial- 7 Jul 1998 2 FourPt(1) U.S. Geological Survey (wrdapp) FourPt(1) differential and integral equations with computers. Exercises are included in the user's manual that demonstrate some of the basic concepts. The model is used as supplement to the course One- Dimensional Streamflow Modeling Concepts (SW2040TC), offered annually at the USGS National Training Center. The course concentrates on basic concepts rather than specifics of the FOURPT model. CONTACTS Operation: U.S. Geological Survey Office of Surface Water Janice M. Fulford Building 2101, Mail Stop 1515 Stennis Space Center, MS 39529 jfulford@usgs.gov 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 FOURPT software can be retrieved are, respectively: http://water.usgs.gov/software/FourPt.html --and-- /pub/software/surface_water/FourPt SEE ALSO branch(1) - One-dimensional Branch-network flow model daflow(1) - Streamflow routine in upland channels of channel networks 7 Jul 1998 3