Water Resources Applications Software

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Summary of FOURPT

       FourPt - An unsteady, one-dimensional, open-channel flow model

       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.

       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.

       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

       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.

       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.

       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
       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

       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).

       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.

       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.

       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-
       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

          U.S. Geological Survey
          Office of Surface Water
          Janice M. Fulford
          Building 2101, Mail Stop 1515
          Stennis Space Center, MS 39529

          U.S. Geological Survey
          Hydrologic Analysis Software Support Program
          437 National Center
          Reston, VA 20192

       Official versions of U.S. Geological Survey water-resources analysis
       software are available for electronic retrieval via the World Wide
       Web (WWW) at:


       and via anonymous File Transfer Protocol (FTP) from:

         (path: /pub/software).

       The WWW page and anonymous FTP directory from which the FOURPT
       software can be retrieved are, respectively:

       branch(1) - One-dimensional Branch-network flow model
       daflow(1) - Streamflow routine in upland channels of
                   channel networks

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