What is the Culvert Analysis Program (CAP)?

The Culvert Analysis Program (CAP) is a solver developed by G.L. Bodhaine at the U.S. Geological Survey (USGS) for developing rating curves for a wide variety of culvert and culvert approach types. The solver was subsequently correct and improved by Janice Fulford of the USGS and then prepared and further corrected for use in iRIC by Keisuke Inoue of Mizuho Instrumentation and Research with direction from Jonathan Nelson, Bob Holmes and many other users at the USGS. Given a suite of information about culvert geometry, approach details and more, the solver produces a culvert rating that predicts culvert flow rates as function of water-surface elevations.

Updated Version of the Culvert Analysis Program (CAP 2021)

CAP 2021 addresses several known computational issues in previous versions of the software and adds support for non-plate corrugated metal pipe arches. CAP version 2021 has been integrated into the International River Interface Cooperative’s (iRIC) numerical simulation software platform as one of several available solvers beginning with iRIC version 4.0. The iRIC software provides a graphical user interface (GUI) front-end for CAP. Versions of CAP that predate version 2021 should no longer be used. Most of the updates correct known inconsistencies with discharge computations for culverts, as documented in Techniques of Water-Resources Investigations of the United States Geological Survey, book 3, chapter A3, “Measurement of Peak Discharge at Culverts by Indirect Methods” (Bodhaine, 1968).