HY8

Evaluation of Drainage Management Software

HY8 was developed by the United States Federal Highway Administration (FHWA) to automate the culvert design methods described in FHWA publications: HDS-5, "Hydraulic Design of Highway Culverts"; HEC-14, "Hydraulic Design of Energy Dissipators for Culverts and Channels"; and, HEC-19, "Hydrology".

The following sections outline the input requirements, computational methods, and output options available with this software. The package was run through various tests for comparison with MTO drainage management practices provided by the MTO Drainage Management Manual (1997). A summary of results, and the requirements for using this software for MTO design, analysis, or approvals is provided.

General Information

Model Capabilities:

Functionality:

Use in MTO Drainage Management Practices:


General Information

Title of Software: HY8
Purpose: Culvert Analysis Software
Publisher: U.S. Department of Transportation Federal Highway Administration
Version: 7.0
Year Published: March 2007
Affiliate Software:  
Platform(s): Windows
Media: Download
System Requirements: -
Availability: Free for download from U.S. DOT, Federal Highway Administration: Hydraulics Engineering

Model Capabilities

What does it do?

HY-8 Culvert Hydraulic Analysis Program can be used to perform calculations for culvert analysis (including independent and multiple barrel sizing), hydrograph generation, hydrograph routing, roadway overtopping and outlet scour estimates. Given all of the appropriate data, HY-8 will compute the culvert hydraulics for circular, rectangular, elliptical, arch and custom culverts using both Imperial and Metric units.

HY-8 Culvert Analysis automates the design methods described in FHWA publications HDS-5, "Hydraulic Design of Highway Culverts," HEC-14, "Hydraulic Design of Energy Dissipators for Culverts and Channels," and HEC-19, "Hydrology." Chapter 5 and Part 4 (Design Charts) in the Ontario Ministry of Transportation (MTO) Drainage Management Manual (DMM) provide a process and methods for detailed hydraulic analysis of culverts. The analysis outlined in the DMM is in line with the design methods found in HDS-5. The theory found in HY-8 can therefore be applied to culverts under MTO jurisdiction because of the similarities between the DMM and HDS-5.

In order to conduct the culvert analysis the user needs to create a culvert file, which, upon creation, asks for the following criteria: design and maximum discharge values, inlet and outlet stations and inverts, culvert material and dimensions, inlet type and inlet conditions, roadway elevation and material, and a tailwater rating curve. These values can be input using the step-by-step method found in HY-8 for creating a new file or existing file (Figure 1) and then filling up the data editor (Figure 2).

HY8 Interface (Figure 1)

Screen Capture of HY8 Interface

HY8InpGen Interface (Figure 2)

Screen Capture of HY-8 Data Editor

How does it do it?

A culvert is a hydraulically short conduit that conveys stream flow through a roadway embankment or past some other type of flow obstruction. Culverts are constructed from a variety of materials and are available in many different shapes.

HY-8 uses the culvert design methodology found in the US Department of Transportation HDS-5 by Normann (1985). This includes the inlet control nomograph equations also found in HDS-5. These equations are basically divided into two conditions of inlet control: submerged culvert and non-submerged culvert. If the culvert inlet is not submerged the inlet performs as a weir. If the inlet is submerged, the inlet performs as an orifice.

HY-8 involves calculating the inlet and outlet control headwater elevations for a given flow. The elevations are then compared and the larger of the two is used as the controlling elevation. In cases where the culvert is not full for any part of its length, open channel computations are performed. In the cases of roadway overtopping (headwater elevation is greater than the roadway embankment) an overtopping analysis based on a broad crested weir formula is conducted where the flow is balanced between the culvert discharge and the surcharge over the roadway. This coincides with the Flow through culverts section in Chapter 5 of the MTO Drainage Management Manual.

File Management

The Windows version of HY-8 saves the Project Files using a “.HY-8” extension. Unlike the DOS version of HY-8, the new version allows any file name format and length allowed by Windows. While HY-8 can read in older version .INP files, to protect this new utility and format, files can only be saved using this new format (and using the new “.HY-8” files extension). In HY-8 associated files are saved inside the HY-8 directory. The *.INP file contains the culvert information, the *.PC file contains the output information after the simulation has taken place and the *.LST file contains the report that was output using HY-8.

Files with the *.DAT extension contain quantitative information regarding the culvert dimensions and sizing. By modifying these files custom culvert sizes can be used. The values input into the culvert can be either in imperial units (ie. Feet and inches) or SI units (Metric i.e. Meter and millimetres etc.).

Output Options

HY-8 can output a report to a file, display it on screen or print it out. The report could of three different types; Standard, Summary or Custom. There is an option of switching the format of the report between Rich Text Format (RTF) or PDF. The report contains the following information:

  • Project data
  • Inlet Elevation
  • Outlet Elevation
  • Culvert Length
  • Culvert Shape
  • Culvert Material
  • Culvert Inlet Type
  • Culvert Flow Values
  • Overtopping Flow Values
  • Summary of Iterative Solution Errors
  • Culvert Performance Curve
    • Discharge Flow
    • Head Water Elevation
    • Inlet Control Depth
    • Outlet Control Depth
    • Flow Type
    • Normal Depth
    • Critical Depth
    • Outlet Depth
    • Tailwater Depth
    • Outlet Velocity
    • Tailwater Velocity
  • Channel Cross Section Information
  • Flow Rating Curve for Downstream Channel
  • Roadway Overtopping Data

The DOS version of HY-8 generated a comprehensive table that could be sent to a text file. However the old version lacked the ability to include graphs and take advantage of formatting in modernword processing programs.

The Windows version of HY-8 includes Report Generation tools that are customizable, allow many options for plots, and are saved in rich text format (RTF) or portable document format (PDF). The primary target for the report is an MS-Word document; however, an rtf format is readable by most Windows-based word processing programs.

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Functionality

Experience Requirements

The software is designed to be self-explanatory, help can be found on almost all screens. An understanding of culvert design is a necessity to create a successful model. Some of the features such as improved inlets, hydrograph generation, routing, and culvert analysis require an experienced user who is familiar with these design methods. Familiarity with all values is necessary in order to complete a successful model. Warning messages will come up if there is information that cannot be processed or calculated.

Using the program

HY-8 asks a series of step-by-step questions. When using HY-8 the user must first create a culvert file or open an existing file. If creating a new file the user is asked for the design and maximum discharge and is then prompted to select whether culvert invert data or embankment toe data will be used for input. The inlet and outlet stations as well as their inverts are required for input. After entering the invert data the user will be prompted to select a type of culvert and input the corresponding parameters for the culvert such as: dimensions, material, inlet type and inlet conditions. A tailwater rating curve must then be selected from the following options: rectangular channel, trapezoidal channel, triangular channel, irregular channel (max 15 coordinates), a customized rating curve or using a constant headwater elevation. The next screen will prompt the user for the rating curve data and a tailwater rating curve will be generated if it was not specified as an option. Options for the roadway surface include a constant roadway elevation and an irregular elevation consisting of 3 to 15 coordinates. After creation of the roadway, a surface or weir coefficient will need to be selected.

Once the culvert data, tailwater curve and roadway surface have been specified the user can choose from a few different types of simulations: Single Culvert (no overtopping), Single Culvert (no overtopping – minimize width), and Multiple Culverts and Overtopping. Rather than using a series of trials to reduce the culvert headwater to an acceptable level the Single Culvert – minimize width option can be used. This will allow the user to perform a culvert design for a circular, box, elliptical and arch shape culvert based on a defined headwater elevation that assumes no overtopping. On selecting this option the user inputs an allowable headwater elevation and the program will adjust the culvert span by increasing or decreasing incrementally until the computed headwater elevation is equal to or less than the allowable elevation. This is a time saver for the user as it prevents repetitively editing a culvert size to obtain a desired headwater elevation.

From the modeled data a report can be generated that can be displayed on screen, printed or output as a Rich Text Format (RTF) or PDF document.

When using the HY-8 input editor, it is necessary to fill out all fields. These fields are required to complete the calculations. If a field is missed or an invalid value is input, an error message will appear notifying the user of the error. The input generator does not have a step-by-step process, but it is organized in a more visually appealing layout and allows the user to edit previously entered data with a few clicks ofthe mouse.

Getting Help

Beyond this and the HDS-5 document, the majority of the HY-8 documentation is self contained within the program. The functional use of the program is documented in the hyper-linked help file available from the Help menu or by selecting help buttons or icons (?) from the graphical user interface. While the help file is organized to provide context-sensitive help, it can be printed out and organized into a hard copy manual.

Comparison with previous versions

Windows and DOS Version: Changes and Additions

An important objective of the conversion of the HY-8 program to a Windows platform (Version 7.0) was maintaining the basic philosophy and simplicity of model input and operation. Additionally, a project development goal was to provide some backward compatibility in reading the existing input files (.INP).

While FHWA and the development team feels these goals and objectives have been largely achieved, there were obviously some things that FHWA wanted to change and add in order to take advantage of the more modern Windows operating system. This section outlines these changes and new features and will serve as a road map to users who have long used the DOS version of HY-8.

The Project File Approach

The new version of HY-8 differs from earlier DOS based version in adopting a Project File approach. These project files are implemented into the Project Explorer – allowing quick selection and application of a specific culvert system2. As described below, the addition of this approach adds utility in (1) organizing and applying culvert systems within multiple drainage crossings and (2) during analyses of different design configurations and materials.

Multiple Drainage Crossings

The DOS version of HY-8 only allowed analysis or design of a single drainage crossing. While the user could define multiple culverts and barrels (systems) at this crossing, if an overall roadway project included many such crossing sites, each would need to be separated into a different input file.

This led to the proliferation of many separate culvert input files associated with a single roadway project. Some practitioners described their confusion in distinguishing which culvert file was associated with which drainage crossing within a project.

In the new version of HY-8, any number of crossings can be defined within the project file. Users now have the option of performing an analysis on several crossings and grouping them together. A new mapping feature (described below) helps the user to create a map identifying each crossing that can be included in their report.

Of course, the Windows version retains older version’s ability to consider only a single drainage crossing. This single crossing can also still consist of multiple culvert systems (e.g., three circular barrels at one invert [system 1] and a box culvert at another invert [system 2] at the same roadway crossing).

Design Alternatives

The new version of HY-8 also provides an improved means to consider separate design alternatives of the same crossing within the same project file. In the DOS version of HY-8, a user would either have to load them as separate files, or make the incremental changes and re-evaluate a single file.

The new version of HY-8 provides the user the option of “copying” a culvert and associated crossing information. With this “duplicate crossing” the user can make any change(s) they wish to evaluate. The project explorer then makes it easy to toggle back and forth between the alternative crossing designs.

File Conventions

The Windows version of HY-8 saves these Project Files using a “.HY-8” extension. Unlike the DOS version of HY-8, the new version allows any file name format and length allowed by Windows. While HY-8 can read in older version .INP files, to protect this new utility and format, files can only be saved using this new format (and using the new “.HY-8” files extension).

Order of Input

The DOS version of HY-8 presented the input as a series of linear, sequential input screens. The order always began with the discharge, followed by the culvert information, followed by the tailwater data, and ended with the roadway information.

In the Windows version of HY-8, a single input screen presents all of the input necessary to analyze a single crossing.

However, there are some important subtleties - the grouping of the information has been organized into “crossing” information and the “culvert” information. The discharge, tailwater, and roadway data are unique to the crossing while the culvert shape, inlet conditions, and site data define a culvert within the crossing.

This grouping, and therefore subsequent tabbing through the main input screen, does not follow the same linear progression of input as the DOS versions of HY-8.

Execution of SINGLE and BALANCE

The DOS version of HY-8 contained separate analysis functions for computing a culvert performance rating curve (SINGLE module), and a roadway overtopping analysis (BALANCE module) that included the effects of all culvert systems within a crossing.

When running this SINGLE module, DOS versions of HY-8 assumed that overtopping was not possible even though roadway data had been defined. Additionally, in the case were there were multiple culvert systems at the same crossing (e.g., a circular culvert and box culvert relatively side-by-side), the old SINGLE approach provided the performance curve of one of the systems
(i.e., circular) assuming that the other system (i.e., box) was not present. One result was users potentially incorrectly applying SINGLE derived performance curve results.

The Windows version of HY-8 performs all culvert analysis considering hydraulic effects of all culvert systems in the crossing as well as roadway overtopping. This means that when you view the performance table (or plot) for a given culvert within the crossing you are seeing the performance within the context of any other culverts and overtopping of the roadway for the crossing and not just as an isolated culvert.

If there is only a single culvert system and the roadway is high enough that overtopping does not occur, the performance curve of the old and new versions match.

Front View

The Windows version of HY-8 contains an option for displaying the front (upstream) view (elevations) of the culvert and roadway at the crossing. From a culvert hydraulics and numerical modeling perspective, computations do not need to consider the lateral placement of culverts within a crossing. Only the elevation relationships between the channel, roadway and other culverts are important. The information requested in the DOS version HY-8 input screens and input files (.INP) reflected this simpler approach. This led to challenges in viewing and plotting these features within the front view area of the updated program.

Roadway Lateral Stationing

To view the (scaled) relationship between the roadway and culvert system in the front view, HY-8 will prompt the user to enter the lateral stationing of the culvert(s) vis-à-vis the roadway.

One reason for requesting this additional value is while irregular shaped roadway sections in HY-8 have always prompted for lateral stations and elevations, the constant elevation option only prompted for a roadway length. This lack of stationing made visual presentation of the culvert location vis-à-vis the roadway problematic3.

In order to allow for the possibility of defining actual stationing along a roadway, the Windows version of HY-8 includes a beginning station as well as the length for constant roadway profiles. The default beginning roadway station ordinate is zero and can be left as zero if actual stationing is not known (or not important).
Lateral stations are defined from the beginning (left, facing downstream) side of the roadway and elevations taken from the upstream invert elevation parameter.

Note on Culvert Barrel plots

To allow backward compatibility with DOS version input files, the new version does not currently plot more than one barrel of a particular system. So while the program plots multiple systems at a crossing, the number of barrels within each system is not plotted. This multi-barrel plotting capability will be added in a subsequent upgrade.

Note on Channel Cross Section plots

As the front view represents the upstream view and because there is no cross section defined for the upstream end of the culvert, no channel cross section is plotted for the front view (the new version of the HY-8 program does plot the downstream channel cross section in a different portion of the program)

The reason for this approach is that in culvert hydraulic practice assumes steady flow, associated with some design frequency. An upstream channel cross section is only needed when considering storage for inflow hydrograph routing. Requiring a user to add these upstream coordinates for a simple culvert layout and this steady flow assumption overly complicates the data requirements and the input process.

Even approaches as simple as projecting the downstream channel along the culvert barrel to the upstream invert were rejected as this assumed a certain positioning of the channel and culvert barrel, as well as assumptions of roadway, barrel, and channel skew.

Background Map

Because multiple crossings can be defined within a single HY-8 project there is an option to create a background map. This map is only a picture and can be defined from any bitmap (.bmp) file. If you are connected to the internet you may search for a roadway or aerial view map online and save the result as your background map. You may also screen capture any image (i.e. a CAD drawing) and save that image as a bitmap (.bmp) file to import and use for your map as well. The map is only used for reference purposes and it or locations defined for culverts have no bearing on any calculations. Currently the map is sent to the report document, but you can cut and paste it into the file by capturing it from the screen.

Report Generation

The DOS version of HY-8 generated a comprehensive table that could be sent to a text file. However the old version lacked the ability to include graphs and take advantage of formatting in modern word processing programs.

The Windows version of HY-8 includes Report Generation tools that are customizable, allow many options for plots, and are saved in rich text format (RTF) or portable document format (PDF). The primary target for the report is an MS-Word document; however, an rtf format is readable by most Windows-based word processing programs.

Known Issues

A few issues related to Report Generation exist with this initial version. These will be corrected in future releases. These issues stem from a problem of placing tables and graphs within document text. In this initial version, each time a table or graph is written to the report, the report starts a new page. This can make reports longer (wasting paper).

This is because of a limitation in the report generation library routines that do not allow tables and graphs to be “docked” in line with text. When trying to condense a report, these tables and plots may cover the text.

Workaround

After exporting a report, manually dock tables in MS Word by selecting the table frame and then right-clicking on the upper left frame border and choosing the Format Frame option. In this screen select the “Remove Frame” button.

For graphs select the graphic and right-click inside choosing the Format Picture option. In this screen choose the Layout tab and then the “In Line with Text” option.

Once these options are set for tables and graphs new page/sections can be deleted and the tables and graphs placed continuously. FHWAs showed its intention to correct this limitation within the library functions used for report generation soon.

Known HY-8 Issues:

A few issues continue to exist in HY-8, most of which are carried over as limitations from the DOS version. The following is a list of these issues:

1. HY-8 does not attempt to show the location of a hydraulic jump in the culvert profile.

2. If more than one flow type exists for the culvert profile, HY-8 does not attempt to show multiple profiles, but only that of the design discharge.

3. NOTE: The user should be aware that when the tailwater elevation exceeds the elevation of the top of the culvert outlet, HY-8 assumes that the barrel flows full at the outlet and reports an outlet velocity corresponding to full flow. A more detailed description of this limitation is given in the Help document under the limitations topic.

4. At this time, the new version of HY-8 does not support several culvert types, such as CONSPAN or HDPE plastic. FHWA intends to add these culvert types in the next upgrade.

5. The new version of HY-8 does not support partially buried culverts or culverts with natural stream bottoms. However, as with the old version, the user may define a user supplied shape that includes different roughness for the sides/top and bottom.

6. The new version of HY-8 does not support culverts with multiple slopes (broken back) and adverse slopes. These are being added in the next phase of this effort.

7. The report functionality in HY-8 will improved to support additional file formats and additional options.

Limitations

Computed outlet velocity and tailwater elevation

The user should be aware that when the tailwater elevation exceeds the elevation of the top of the culvert outlet, HY-8 assumes that the barrel flows full at the outlet and reports an outlet velocity corresponding to full flow. The water surface profile for these cases is not realistic. In effect, HY-8 assumes a type of hydraulic jump occurs in the barrel. This may or may not be the case; HY-8 does not include a momentum analysis to truly determine if and where a hydraulic jump might occur. If, indeed, a hydraulic jump does occur, then the reported outlet velocity is correct. If not, then the outlet velocity reported in HY-8 may be too low. Caution must be exercised in these cases.

When the elevation of the tailwater does not exceed that of the top of the culvert outlet, then a profile indicating outlet velocity associated with supercritical flow depth in the culvert barrel. In effect, HY-8 will indicate that no hydraulic jump will occur. If this is the case, then the outlet velocity will be normal. If not, the outlet velocity will be too high and energy dissipation should be considered.

Hydraulic Jumps

HY-8 does not attempt to show the location of a hydraulic jump in the culvert profile. Additionally, if more than one flow type exists for the culvert profile, HY-8 does not attempt to show multiple profiles.
NOTE: The user should be aware that when the tailwater elevation exceeds the elevation of the top of the culvert outlet, HY-8 assumes that the barrel flows full at the outlet and reports an outlet velocity corresponding to full flow. A more detailed description of this limitation is given in the Help document under the limitations topic.

Culvert Types

The following types of culverts are still not available:

  1. There are several culvert types, such as CONSPAN or HDPE plastic, which were unsupported in MS-DOS HY-8 and will continue to be unsupported in HY-8 version 7.0.
  2. Partially buried culverts or culverts with natural stream bottoms remain unsupported in HY-8 version 7.0.

Broken Back Culverts

Culverts with multiple slopes (broken back) and adverse slopes remain unsupported by this version of HY-8.

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Use in MTO Drainage Management Practices

Minimum Requirements for Inclusion in Report

This section provides some guidance to designers, analysts and reviewers on the type of information and minimum requirements for reporting the results of a HY-8 analysis. This by no means should be considered a comprehensive list of the information included in a drainage report.

Relevant Input

A summary of the input data is required; all of this information is included in the report generated by HY-8. A summary of which computational methods were used for rainfall simulation and peak flow estimation should be included as well as the source of coefficients. Any variance from accepted practise should be explained.

Tabular and Graphical Output

The report should include both tabular and graphical output showing the water elevation versus flow rate as minimum for each culvert analyzed. A table summarizing the culvert flows as well as a summary of the iterative solution errors for the overtopping elevations. The overtopping flows should be explained as well as recommendations made if necessary. Any other variables pertinent to the reports recommendations should also be supported by tabular and graphical output. (i.e. outlet velocities for erosion concerns, tailwater depth).

A summary of output data should be provided. Also, the ASCII text output file is required so that the reviewer can obtain all necessary output data and can see the values used in the graphical output.

A culvert performance curve should be generated and included in the report. The windows based HY-8 Version 7.0 outputs the data into well-organized and concise tables, and can plot the water elevation versus flow rate for the headwater, culvert(s), roadway and tailwater all onto one graph that can be easily exported.

Crossing - Hwy 64 - Wolf River, Design Discharge Chart

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