The following is one of over 75 programs & documentation included with Hydro-CD by Dodson

CGAP - Channel Geometry Analysis Program

VERSION/DATE: Version: 3.5 1995/10/06




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.


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 elevations (stage) from data that consist of coordinate pairs of cross-channel distances and land-surface of 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 CGAO). 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. 


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.


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).

2012 - Walter P. Moore & Associates, Inc. - Houston, TX, USA