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Bridges & Structures

HY-8 Culvert Hydraulic Analysis Program

HY-8 automates culvert hydraulic computations utilizing a number of essential features that make culvert analysis and design easier. An HY-8 User Manual is included with the software installation (access via 'Help' button on top toolbar) to provide important information on the technical features, capabilities, and limitations of the software.

System Compatibility

HY-8 is a 64-bit program, and only compatible with 64-bit Windows-based operating systems. When installing HY-8, make sure you have permissions on your computer to install programs (usually this requires administrator permissions or a username and password for an administrator account). If you do not have administrator permissions on your account, you need to right-click on the installation program and select the "Run as Administrator" option.

HY-8 has been updated to improve 508 compliance. The program can now be navigated with the keyboard with increased menu tools and navigation. Each dialog was reviewed for keyboard navigation. The documentation has been updated to follow 508 compliance by using formatting, style sets, and alternate text for images. The report generator was updated to use style sets.

Download Agreement

By downloading the software, users acknowledge that they have read and agree to the following conditions:

  • The application of this software is the responsibility of the user. It is imperative that the responsible designer understands the potential accuracy limitations of the program results, independently cross checks those results with other methods, and examines the reasonableness of the results with engineering knowledge and experience.
  • There are no expressed or implied warranties.

I agree to these conditions when downloading the software.

HY-8 Version 7.70

Build date: June 2, 2021. Download HY-8 Version 7.70 (.zip, 153 mb)

Improvements made to this version of the software include the following:

  • Added a secondary versioning number.
  • Updated the Quick Start Guide.
  • Upgraded the interface for high pixel density displays and updated interface icons.
  • Upgraded to a new library to export data to the report generator with Microsoft Word format (DOCX).
  • Added an option to set default unit system, outlet control, and exit loss.
  • Added irregular roadway plot minimum and maximum crest elevations in the side view.
  • Increased the number of irregular roadway plot points from 15 to 5000.
  • Added Manning’s n value and plot of critical depth in the tailwater channel.
  • Added feedback to the user when irregular tailwater channel is insufficient for the specified flow.
  • Improved HY-8 tailwater computations to better handle surcharge situations.
  • Added culvert size on the results page.
  • Added Ke value of the inlet edge types and the culvert barrel slope in the Edit Crossing window.
  • Added max shear stress to the AOP table.
  • Provided testing information to the user in the HY-8 User’s manual.

Bug fixes include:

  • issue with runtime error report
  • discontinuity in reported outlet control depth
  • toggles in performance table with “all on” or “all off” commands
  • error when exporting report
  • issue with tailwater depths and unreasonable computation time
  • internal testing issue
  • issues with images not being removed and project notes not being cleared
  • issue of anomaly when exporting a report
  • issue of embedment not being exported in the report
  • issue with file size increasing with each read and save cycle
  • issue with computing the Froude Number in the energy dissipation module
  • issue where HY-8 stops running on some machines
  • issue with entering negative tailwater elevation
  • issue with adversely sloped outlet control culvert flowing full instead of following a drawdown curve
  • issue with Performance curve plot in SI units
  • issue with ‘Root was not bracketed’
  • issue with double broken-back culvert not completing the water surface profile and providing a false outlet velocity
  • ‘Define Roadway Stations’ crash
  • HY-8 handling of negative stationing with a broken-back culvert
  • issue with Ke values not being applied properly
  • issue with embedded plots when saving and changing the inlet

HY-8 Version 7.60

  • Build Date July 30, 2019. This version does not include new features, but rather: 1) corrects computational issues with embedded circular culverts, 2) fixes many reported bugs, 3) improves computational stability, and 4) updates the user interface. The HY-8 User’s Manual included with the software package (available by selecting “HY-8 Help” in the “Help” drop-down menu) describes the corrections to the embedded circular culvert logic in Section 4.1, Embedment Depth. Please email Eric Brown (eric.r.brown@dot.gov) if you want additional details on the implemented corrections to embedded circular culverts and a complete list of maintenance items implemented in Version 7.60.

HY-8 Version 7.50

  • Build Date July 28, 2016. This version contains two new calculators: a) a calculator to assist with the FHWA's culvert aquatic organism passage (AOP) design procedure, which is described in detail within Hydraulic Engineering Circular 26, "Culvert Design for Aquatic Organism Passage, First Edition" (HEC-26), and b) a calculator to determine the variation in cross-sectional flow velocity from the culvert wall to the centerline, which is described within Research Publication No. FHWA-HRT-14-064, "Fish Passage in Large Culverts with Low Flows".

    Improvements made to this version of the software include: corrections to the AOP calculator, a correction to the calculation of roadway overtopping for various scenarios, a correction to the calculation of composite Manning's n values for user defined shapes, edits to the Saint Anthony Falls (SAF) Energy Dissipator routine, and edits to the Riprap Basin Dissipator routine.

Reporting Issues

If you believe you have found an issue with any version of HY-8 (including installation errors, calculation errors, interface problems, confusing functions, errors and omissions in the User Manual, and anything else that might impact the functionality and usability of the software), please submit the following information to CommentsOnHY8@dot.gov (please note that in most cases you will not receive a personalized email response from the email administrator):

  • Name
  • Contact info (this won't be used unless there is a question about your HY-8 issue)
  • Computer operating system (Windows 8, Windows Vista, etc.)
  • Complete description of each issue
  • PLEASE attach the HY-8 project file (.hy8) that demonstrates the issue
  • Also consider attaching a screen shot of the HY-8 window if applicable
Updated: 09/23/2021
Federal Highway Administration | 1200 New Jersey Avenue, SE | Washington, DC 20590 | 202-366-4000