Evaluation of Drainage Management Software

Software Reviewed: HY8

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.

Model Capabilities

What does it do?

HY8 Culvert Analysis 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, HY8 will compute the culvert hydraulics for circular, rectangular, elliptical, arch and custom culverts using both Imperial and Metric units.

HY8 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 based on HDS-5. HY8 can therefore be applied to culverts under MTO jurisdiction.

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 in a step-by-step process in the dos environment using HY8 (Figure 1) or they can be input in a Windows environment using the HY8InpGen (Figure 2) add-on application.

Figure 1 - HY8 Interface

Figure 2 - HY8InpGen Interface

Designing the culvert in HY8, the culvert dissipator application can be used. Hydraulic parameters computed in the culvert design program can be imported into the energy dissipator application. An internal or external energy dissipator can be simulated with various categories for each. Some of the energy dissipators that can be selected include drop structures and stilling basins. After selecting the desired dissipator, the restrictions and limitations of the dissipators are presented in a table format for each category on the screen.

How does it do it?

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

HY8 uses the culvert design methodology found in the US Department of Transportation HDS-5 by Normann (1985). This includes the inlet control and outlet control nomograph equations found in HDS-5. HY8 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. The flow then is balanced between the culvert discharge and the surcharge over the roadway.

File Management

In HY8 files are saved in four different formats. All of the files are saved in the HY8 directory. When creating a new file in HY8, the interface asks the user to select a name for the file. The same name is then assigned to all the files with different extensions. 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 HY8. Files with the *.DAT extension contain quantitative information regarding the culvert dimensions and sizing. By modifying these files, custom culvert sizes can be used. Each of these files can be created and accessed using the HY8 DOS version as well as using the Windows HY8 input generator and HY8 PC viewer.

Output Options

After inputting all the data into the interface the user can access the printing options by pressing <R>, for report, on the main screen. In the printing options the user can pick between how many pages does the heading has to appear on, where should the page number appear on each page, output to printer or screen and the type of report, full or summary. The summary outputs only the first three screens of the complete report and therefore is not recommended.

The report is initially in an ASCII text base format (Figure 3) however, when it is opened using HY8PCViewer the report is organized into a tabular and graphical format, as shown in Figure 4, which may then be outputted into HTML files or a bitmap image. The report contains the following information:

• 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

Figure 3 - ASCII Report format

Figure 4 - Tabular and Graphical Report

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Functionality

Experience Requirements

The program is designed to walk the user through the step-by-step progress. A good understanding of culvert design is required to use HY8 design. The help option can be found on almost all of the screens. Some of the features such as improved inlets; hydrograph generation, routing, and design of energy dissipator require an experienced user who is familiar with these design methods.

When using the Windows HY8 input generator, the step-by-step guided input process is not used like in HY8 so familiarity with all values is required in order to complete a successful simulation. Warning messages will appear if there is information that cannot be processed or calculated.

Using the program

HY8 asks a series of step-by-step questions. When using HY8 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 text document.

The software offers a choice of three pipe material types. It sets default values for manning's "n" for each pipe type. However, the user may change this value if desired.

The pipe material type and values are:

When using the HY8 input generator, it is necessary to fill out all fields marked with a blue background. 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 of the mouse.

HY8 provides for selecting different types of end treatments. These include:

• Square Edge with headwall
• Grooved end projection
• Grooved end in headwall
• Bevelled edge (1:1)
• Bevelled edge (1.5:1)

Bevelled inlets are formed tapers on the inside of the concrete top slab in the case of concrete culverts.

Comparison with previous versions

The Pennsylvania state university in cooperation with the US Department of Transportation Federal Highway Administration (FHWA) produced HY8 versions 1.1, 2.1, and 3.0. HY8 versions 3.1, 4.1 and 6.0 have been developed by Philip L. Thompson and have been provided to the FHWA for distribution. HY8 Version 6.0 (Energy, HYD and Route) was produced by GKY and associates under contracts with the FHWA.

Between version 6.0 and 6.1 of HY8 there were only minor changes to the functionality of the program and a few bug fixes. A HY8 PC Viewer and Input Generator application was also introduced that moves HY8 from a DOS based application to using a windows based interface. The windows based input generator and PC viewer still require the HY8 DOS based application to function.

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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 HY8 analysis. This by no means should be considered a comprehensive list of the information included in a drainage report.

Input

Drainage Report must include the followings:

• The Full report with heading on each page and the report should include both tabular and graphical outputs showing:
  • The water elevation versus flow rate 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 the input data is required; all of this information is included in the report generated by HY8.
• A summary of computational methods used for rainfall simulation used for estimating and peak flow estimation as well as the source of coefficients.
• Any variance from accepted practise should be explained.
• Tabular and Graphical Output
• The ASCII test output file
• The culvert performance curve should be generated and included in the report.

The HY8PCViewer outputs the data into well-organized and concise tables showing plot of water elevation versus flow rate for the headwater, culvert(s), roadway and tailwater all onto one graph that can be easily exported.

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