NAME
cgap - Channel Geometry Analysis Program
ABSTRACT
CGAP permits the analysis, interpretation, and quantification of the
physical properties of an open-channel reach as defined by a
sequence of cross sections. The primary function of the program is
to compute the area, width, wetted perimeter, and hydraulic radius
of cross sections at successive increments of water-surface
elevation (stage) from data that consist of coordinate pairs of
cross-channel distances and land-surface or channel-bottom
elevations. Longitudinal rates-of-change of cross-sectional
properties are also computed. In addition, the mean properties
(including discharge as computed using the Manning's equation) of a
channel reach and the cross-sectional area and channel widths as
functions of stage for subdivisions of a cross section can be
computed. CGAP was developed to compute, display, and otherwise
format cross-sectional data for use with simulation models. CGAP
produces files of data in the required input format for BRANCH and
HSPF (the latter after use of the program genftbl--generate F-
Table--provided with CGAP). CGAP has 17 output options that produce
the following forms of output: tabular lists, sequential files, and
(or) graphical plots in digital or line-printer format.
HISTORY
Version 3.5 1995/10/06 - Enhancement to include output of wetted
perimeter for mean group option 6 (BRANCH model geometry table).
Version 3.3 1995/07/18 - Code clean-up and bug fixes, print
Manning's value and wetted perimeter for subdivision tables.
Version 2.7 1994/02/15 - Added automatic update of revision number
and date, completed port to DOS-based computers, made minor bug
fixes and code cleanup.
Version June 01, 1993 - Added option 17, which produces mean groups
of cross-sectional properties including discharge as a function
of stage as computed using Manning's equation. Option 16
modified to allow computation of discharge for subdivisions of
cross sections based on horizontally varying roughness.
Version 92/02/01 - First Hydrologic Analysis Software Support
Program release, code cleaned up and made UNIX compatible.
Version 91/09/05 - First UNIX release.
Version 90/12/05 - Improved interactive update of existing CGAP
input records, allowing selective processing of a subset of the
input cross sections.
DATA REQUIREMENTS
Input data consists of land-surface or channel-bottom elevations
measured and referenced horizontally to a channel-bank location and
referenced vertically to a common datum. These data should be
measured along a line normal to the flow direction at the thalweg of
the channel. Sufficient number of points must be obtained so that
linear interpolation between points accurately describes the cross-
sectional properties at all possible stages of flow. A minimum of
two data points below and a single channel must be present at the
minimum elevation of interest in order for CGAP to perform
computations. Other input data include datum adjustments, segment
lengths, skew angles, and program-control parameters, such as output
options, stage range of computations, computation increment, and
plot scaling factors. Input is expected in the inch-pound system of
units.
OUTPUT OPTIONS
The program provides 16 output options that format the input cross-
sectional data or the computed cross-sectional properties as digital
plots, line-printer plots, tabular lists, and (or) sequential files.
These output formats include: plots of cross sections; plots of
cross-sectional area and (or) channel width as functions of stage;
tabular lists of computed, stage-dependent, cross-sectional
properties (area, width, wetted perimeter, hydraulic radius, average
depth, and symmetry); files of computed cross-sectional properties;
plots of cross sections in isometric projection; plots of cross-
sectional area at fixed stage as a function of longitudinal distance
along an open-channel reach; files of computed cross-sectional area
as a function of stage for subdivisions of a cross section; and
files of computed discharge, area, top width, and conveyance as
functions of stage for mean groups of one or more cross sections.
Output is in the inch-pound system of units. The graphical output
is dependent on the capabilities of the graphics library linked with
the program (either GKS or CalComp compatible).
SYSTEM REQUIREMENTS
CGAP is written in Fortran 77 with the following extensions: use of
include files, variable names longer than 6 characters, and
reference to compiler-dependent system date and time routines. CGAP
requires a utility library (libutl) that includes the software/user,
software/computer, and software/graphics interaction routines. CGAP
graphics are coded using CalComp graphics calls. The libutl
software provides graphics libraries to convert CalComp graphic
references to Graphical Kernel System (GKS) library references and
Interactive Software Services's INTERACTER library references.
Generally, the program is easily installed on most computer systems
that have access to one of the mentioned graphics libraries. 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.
DOCUMENTATION
Regan, R.S., and Schaffranek, R.W., 1985, A computer program for
analyzing channel geometry: U.S. Geological Survey Water-
Resources Investigations Report 85-4335, 40 p.
TRAINING
Implementation and Calibration of Unsteady Open-Channel Flow
Transport Models (SW3091TC), offered annually at the USGS National
Training Center.
CONTACTS
Operation 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 CGAP
software can be retrieved are, respectively:
http://water.usgs.gov/software/cgap.html
--and--
/pub/software/surface_water/cgap
--and--
/pub/software/general/libutl
SEE ALSO
branch(1) - One-dimensional Branch-network flow model
libutl(1) - Utility libraries for simulation models