

CGAP  Channel Geometry Analysis Program VERSION/DATE: Version: 3.5 1995/10/06 OPERATING SYSTEM: DOS DISTRIBUTOR: USGS DOCUMENTATION (62 Pages) Regan, R.S., and Schaffranek, R.W., 1985, A computer program for analyzing channel geometry: U.S. Geological Survey WaterResources Investigations Report 854335, 40 p. ABSTRACT CGAP permits the analysis, interpretation, and quantification of the physical properties of an openchannel 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 watersurface elevations (stage) from data that consist of coordinate pairs of crosschannel distances and landsurface of channelbottom elevations. Longitudinal ratesofchange of crosssectional properties are also computed. In addition, the mean properties (including discharge as computed using the manning's equation) of a channel reach and the crosssectional 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 crosssectional 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 genftblgenerate FTableprovided 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 lineprinter format. DATA REQUIREMENTS Input data consists of landsurface or channelbottom elevations measured and referenced horizontally to a channelbank 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 crosssectional 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 programcontrol parameters, such as output options, stage range of computations, computation increment, and plot scaling factors. Input is expected in the inchpound system of units. OUTPUT OPTIONS The program provides 16 output options that format the input crosssectional data or the computed crosssectional properties as digital plots, lineprinter plots, tabular lists, and (or) sequential files. These output formats include: plots of cross sections; plots of crosssectional area and (or) channel width as functions of stage; tabular lists of computed, stagedependent, crosssectional properties (area, width, wetted perimeter, hydraulic radius, average depth, and symmetry); files of computed crosssectional properties plots of cross sections in isometric projection; plots of crosssectional area at fixed stage as a function of longitudinal distance along an openchannel reach; files of computed crosssectional 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 inchpound system of units. The graphical output is dependent on the capabilities of the graphics library linked with the program (either GKS or CalComp compatible). 
