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
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-
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