cgap(1) U.S. Geological Survey (wrdapp) cgap(1) 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 7 Jul 1998 1 cgap(1) U.S. Geological Survey (wrdapp) cgap(1) 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 7 Jul 1998 2 cgap(1) U.S. Geological Survey (wrdapp) cgap(1) 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 7 Jul 1998 3