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Water Resources of the United States


Culvert Analysis Program
CAP Graphical User Interface

The 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 peak discharge through culverts from high water marks. It will compute flows for rectangular, circular, pipe arch, elliptical, and other nonstandard shaped culverts. CAPGUI is a stand-alone Java Archive (JAR) that interfaces with the CAP command-line Fortran program. CAP solves the 1-D steady-state energy and continuity equations for upstream water-surface elevation given a discharge, approach and culvert properties, and a downstream water-surface elevation. The basic technique is presented in Measurement of Peak Discharge at Culverts by Indirect Methods (G.L. Bodhaine,1968). The program can be used to compute rating surfaces or curves that describe the behavior of flow through a culvert or to compute discharges from measurements of upstream and downstream water-surface elevations. CAPGUI provides a graphical wrapper around CAP to assist the user in developing the required input files and viewing the results.

CAP requires measurements of culvert geometry, culvert roughness, and culvert inlet, and measurements of approach section geometry and roughness. Results include (1) a detailed report that summarizes the culvert computations and (2) optional table of the discharges, tailwaters, and upstream water-surface elevations computed.

Current Version:

CAP 2011
CAP - 2.0
CAPGUI - 1.1

Release Date: May 2017
Documentation: NOTE: Electronic and/or print versions of many U.S. Geological Survey reports can be found at the Publications Warehouse (
Bradley, D. Nathan, Culvert Analysis Program Graphical User Interface 1.0--A preprocessing and postprocessing tool for estimating flow through culvert: U.S. Geological Survey Fact Sheet 2013-3045, 4 p. [PDF] | [Online].
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. [PDF].
Fulford, J.M., 1995, User's guide to the Culvert Analysis Program: U.S. Geological Survey Open-File Report 95-137, 69 p. [PDF].
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. (
Version History ( release.txt )
Software User Rights Notice
Contact: U.S.Geological Survey
Office of Surface Water
415 National Center
Reston, VA 20192

Distribution Files

20 October 2021 The CAP distribution files are temporarily unavailable. A new version of CAP will be released soon, and at that time the distribution downloads will be re-enabled. Please contact The Office of Surface Water if you need support.
Version Operating System Download File Description

CAP 2011


CAP 2.0


README.txt Installation and usage information
(86 MB)
Updated program (Windows), includes executable program

CAP 97-08c




README.TXT Installation and usage information
cp9708c.exe (553K) Includes executable program, test data, and documentation (no source code)
cp9708cs.exe (334K) Includes source code, test data, and documentation (no executable program)
UNIX README.TXT Installation and usage information
Cap97.08c.Solaris.tar.gz (507K) Compressed tar file, includes Sun Solaris executable program, test data, and documentation (no source code)
Cap97.08c.SGI.tar.gz (507K) Compressed tar file, includes Silicon Graphics Indigo executable program, test data, and documentation (no source code)
Cap97.08c.source.tar.gz (304K) Compressed tar file, includes source code, test data, and documentation (no executable program)

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