Water Resources Applications Software

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Summary of CAP

       Cap - Culvert Analysis Program

       CAP follows USGS standardized procedures for computing flow through
       culverts.  It can be used to develop stage-discharge relationships
       for culverts and to determine discharge through culverts from high
       water marks.  It will compute flows for rectangular, circular, pipe
       arch, elliptical, and other nonstandard shaped culverts.

       The program solves the 1-D steady-state energy and continuity
       equations for upstream water-surface elevation given a discharge and
       a downstream water-surface elevation.

       Version 97-08c 1999/11/15 - Defined variable that was defaulting to
          unintended data type and causing divide-by-zero error.

       Version 97-08b 1999/09/03 - Code fixed to ensure 0 returned for one
          function when flow equation root doesn't close to specified
          criteria.  Minor corrections made in display of warning messages.

       Version 97-08a 1998/12/07 - Elliptical culvert sections added.

       Version 97-08 1997/08/30 - Version as documented in USGS Water-
          Resources Investigations Report 98-4166.

       Version 97-01 1997/05/01 - Several additions have been made to the
          CAP program to reduce the effort required to assemble input data.
          The major new features are: (1) metric conversion options (a new
          record implements this feature); (2) default values for C5 and
          C46 coefficients; (3) new input record for geometry data for
          inlet details.

          The following describes problems in the code that have been
          corrected.  The *CF record variable, HFLW, did not affect
          computations as was stated in Open-File Report 95-137.
          Meaningless fall and loss values for computations made by
          linearly interpolating between high head and low head flows were
          included in results.  For nonstandard culvert descriptions using
          the *CS record, if the left-most coordinate pair was not entered
          first on the *CS record, an erroneous width was printed in the
          results.  Skew angles entered on the XS record that describes the
          approach section geometry did not affect the computations.  The
          CG record variable, ICODE, did not affect pipe arch computations
          appropriately.  The report also neglected to state that the J
          portion of the ICODE is required for pipe arches.  The J portion
          of the ICODE should be entered for pipe arches and indicates the
          material used and, for corrugated pipe, the corner radius of the
          pipe when BOTRAD, TOPRAD, and CORRAD are not specified.  Omission
          of a valid J value will result in the program failing to work.
          The J codes are as follows:

          1- concrete pipe, 2,4- corrugated metal pipe, corner radius<= 18"
          3- aluminum pipe, 5- corrugated metal pipe, corner radius = 31"
          6- corrugated metal pipe, corner radius = 47"

          These codes may not be compatible with WSPRO J codes for some

       Version 94-10 1995/10/31 - Version as documented in USGS Open-File
          Report 95-137.

       1993 - The CAP program was developed using an antecedent program,
          A526, as a guide for some of the routines.  Several features that
          were not available in A526 were included.  These features are
          computations for nonstandard culvert sections, default
          computation of discharge coefficients for flow types 1, 2, and 3,
          computation between flow transitions, and input file formats that
          are compatible with WSPRO input formats.

       Measurements of culvert geometry, culvert roughness, and culvert
       inlet, and measurements of approach section geometry and roughness.

       Two outputs are available--a condensed table of computed values that
       is meant for use by other computer programs and a text form that
       summarizes the computations made by the program.

       The program is written in Fortran 77 with the following extensions:
       include files, variable names longer than 6 characters, and common
       block with character and noncharacter variables.  Generally, the
       program is easily installed on most computer systems.  The code has
       been used on UNIX-based computers and DOS-based 386 or greater
       computers having a math coprocessor.

       Bodhaine, G.L., 1968, Measurement of peak discharges at culverts by
          indirect methods:  U.S. Geological Survey Techniques of Water-
          Resources Investigations, book 3, chap. A3, 60 p.

       Fulford, J.M., 1998, User's guide to the U.S. Geological Survey
          Culvert Analysis Program, Version 97-08:  U.S. Geological Survey
          Water-Resources Investigations Report 98-4166, 70 p.

       Surface-Water Hydraulic Analysis (G0093), offered annually at the
       USGS National Training Center.

       Operation and Distribution:
          U.S. Geological Survey
          Hydrologic Analysis Software Support Program
          437 National Center
          Reston, VA 20192

       Official versions of U.S. Geological Survey water-resources analysis
       software are available for electronic retrieval via the World Wide
       Web (WWW) at:


       and via anonymous File Transfer Protocol (FTP) from:

         (path: /pub/software).

       The WWW page and anonymous FTP directory from which the CAP software
       can be retrieved are, respectively:


       If you would like to obtain the price of and (or) order paper copies
       of USGS reports, contact the USGS Branch of Information Services at:

                  USGS Information Services
                  Box 25286
                  Denver Federal Center
                  Denver CO 80225

       To inquire about Open-File Reports or Water-Resources Investigations
                  Tel: 303-202-4200; Fax 303-202-4695

       To inquire about other USGS reports:
                  Tel: 303-202-4700; Fax 303-202-4693

       wspro88(1) - A computer model for Water-Surface PROfile

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