HY8:Differences from DOS HY-8

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Differences Between DOS HY-8 and HY-8 7.0

An important objective of the conversion of the HY-8 program to a Windows environment was maintaining the basic philosophy and simplicity of model input and operation. While we believe this has been largely achieved, there were obviously some things that we wanted to change and add in order to take advantage of the more modern Windows operating system. This page outlines these changes and new features and will serve as a roadmap to users who have long used the DOS version of HY-8.


Previous versions of HY-8 allowed for a single crossing to be designed. Multiple culverts and barrels could be defined, but in a given project only the culvert design information for a single roadway crossway could be defined and analyzed. If in the context of a larger design project multiple crossings needed to be analyzed then each one was defined in a separate input file. In HY-8 version 7.0 any number of crossings can be defined within the same project. While it is just as simple to have a single crossing, mimicking older versions of HY-8, there is also the option of performing an analysis on several crossings and grouping them together. The new mapping feature described below helps create a map identifying each crossing that can be included in the report. The concept of multiple crossings can also be used to represent separate design alternatives of the same crossing within the same project file. In previous versions of HY-8 a user would either have to load them as separate files or make the incremental changes and reevaluate. In version 7.0 of HY-8 there is the option of “copying” a crossing and then the user can make the changes to evaluate. The project explorer then makes it easy to toggle back and forth between the alternative crossing designs.

Order of Input

The MS-DOS versions of HY-8 presented the input as a series of linear input screens. The order always began with the discharge, followed by the culvert information followed by the tailwater data and ending with the roadway information. In this new Windows compatible version of HY-8 all of the input necessary to analyze a single crossing is presented in the same input screen. However, the grouping of the information has been organized into the “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 previous versions of HY-8.

Execution of SINGLE and BALANCE

The MS-DOS versions of HY-8 contained separate analysis functions for computing a culvert performance rating curve (SINGLE), and a roadway overtopping analysis (BALANCE) that included the effects of all culverts within a crossing. When running SINGLE, HY-8 assumed that overtopping was not possible even though roadway data were defined. In HY-8 version 7.0 all culvert analysis is done with all culverts in the crossing and roadway overtopping as considerations (BALANCE). This means that when viewing the performance table (or plot) for a given culvert within the crossing, the user sees the performance within the context of any other culverts and overtopping of the roadway for the crossing and not just as an isolated culvert as was the case with SINGLE in older versions of HY-8. If there is only a single culvert and the roadway is high enough that overtopping does not occur, the performance table of HY-8 version 7.0 would match older versions.

Front View

HY-8 version 7.0 contains an option for displaying the front view (elevations) of the culvert and roadway at the crossing. Hydraulic computations in version 7.0, like older versions, are not a function of the lateral placement of culverts within a crossing. Only the elevation relationship to the roadway and other culverts is important. However, if viewing this relationship in the front view, HY-8 will prompt to enter the lateral stationing of the culverts. While irregular shaped roadway sections in HY-8 have always prompted for lateral stations and elevations, the constant elevation option only prompted for a length. In order to allow for the possibility of defining actual stationing along a roadway HY-8 now includes a beginning station as well as the length for constant roadway profiles. The default is zero and can be left as zero if actual stationing is not known or important. Lateral stations for culverts are defined from the beginning (left) side of the roadway and elevations were taken from the upstream invert elevation parameter. Cross section information is generally provided at the downstream end of the culvert, but the front view represents the upstream view and because there is no cross section defined for the upstream end of the culvert, no cross section is plotted for the front view. A user can change the station of a culvert once entered in the same way by right-clicking in the front view plot window and choosing the menu option to edit the culvert station.

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. When connected to the internet, search for a roadway or aerial view map online and save the result as the background map. A user 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 the 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 a user can cut and paste it into the file by capturing it form the screen.

Report Generation

With previous versions of HY-8 a comprehensive table could be generated and sent to a text file, however, the ability to include graphs and take advantage of formatting in modern word processing programs was lacking. The Report Generation tools in HY-8 7.0 are customizable, include many options for plots and are saved in rich text format (*.rtf) and portable document file (*.pdf). The first target is an MS-Word document; however, the *.rtf format is readable by most Windows-based word processing programs. A few limitations exist with the library used to export reports to these formats. These limitations stem from a problem of placing tables and graphs within document text. In this first version, each time a table or graph is saved a new page is started. This is because of a limitation in the library routines being used that does not allow tables and graphs to be “docked” in line with text. After exporting a report, manually dock tables in MS Word by selecting the table frame and then right-clicking on the frame border and choosing the Format Frame option. In this screen select the Lock Anchor option. 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.