A culvert is a hydraulically short conduit, which can be used to convey stream flow underground through a roadway embankment or other flow obstructions, or used as an outlet structure attached to a detention pond. Culverts come in circular and rectangular cross sections, and concrete, corrugated steel, aluminum and plastic materials.
The hydraulics of a culvert are complex since several flow control types may exist. The methods that Pipe Culvert Design uses are from FHWA Hydraulic Design Series No. 5 (HDS-5), Hydraulic Design of Highway Culverts. There are two flow controls: inlet control and outlet control. Under inlet control, the culvert's entrance characteristics determine it's capacity, and the culvert is capable of conveying a greater discharge than the inlet will accept. With outlet control, the inlet can accept more flow than the culvert can carry because of the head loss due to the friction along the barrel or the high tailwater elevation. Furthermore, because culverts are generally not long enough to achieve uniform flow, the flow profile inside is often gradually or rapidly varied flow. In Pipe Culvert Design, bother inlet control and outlet control calculations are performed, along with the gradually varied flow analysis. The worst-performing control condition is then used to evaluate the proposed design, i.e. the greater of the inlet control headwater and the outlet control headwater is the controlling headwater. Please refer to HDS-5 for details.
From the Structure menu in the Hydrology Module, choose Pipe Culvert
Design to display the design dialog. Click on Load button to load an
existing culvert file to view or modify it, or a new file to start a
fresh
design. From the Solve For list, select the value that you want to
calculate. The available values are: Discharge, Headwater and Size.
|
| Culvert Design |
From the Shape list, select the type of culvert that you want to define. The available shapes are Circular and Box. From the Material list, select the material for the culvert, the available options are Concrete or CMP/Aluminum. If you don't solve for the culvert size, enter the values in the Diameter box or Height and Width boxes depending on the culvert shape. In the Manning's n box, type a Manning's n roughness coefficient for the culvert. You can also click on Select button to select a coefficient from the Manning' n Library. Please refer to Pipe Manning's N Library for defining Manning's n values. In the Number of Barrels box, enter the number of barrels for the culvert.
The Inlet list contains the different inlet types available for the current culvert shape. It updates with different culvert shape that is chosen. All the inlet types are specified in HDS-5. Ke is the entrance loss coefficient, which is depending on the culvert shapes and inlet types. It'll update with different chosen culvert shape and inlet type, you can also type the value in the box.
Inlet Invert is the elevation of the bottom of the culvert at the upstream end, while Outlet Invert is the elevation of the bottom of the culvert at the downstream end. In the Length box, enter the true culvert pipe length. The culvert slope will be calculated after entering the above three values and displayed in the Slope box. You can also change the outlet invert by entering a slope for the culvert.
In the Discharge box, enter the rate of flow in the culvert. In the Headwater Elev box, enter the water surface elevation at the upstream end of the culvert. If you are solving for either discharge or headwater, the corresponding box will be disabled. In the Tailwater Elev box, enter the water surface elevation at the downstream end. Section Size Library allows you to specify as many as available pipe sizes for solving for culvert size. After the hydraulic calculation, the smallest, large enough, available pipe size will be chosen. Please refer to the Pipe Size Library command for defining pipe sizes. Click on Solve button, depending on Solve For selection, the headwater, discharge, culvert size are calculated and displayed in the dialog correspondingly. The Outlet Velocity and Flow Depth are calculated and shown, and the Control Type is also illustrated.
Click on the Stage-Discharge Result button to display the stage-discharge curve in the Stage-Discharge Result Dialog. From this dialog, you can view the stage-discharge curve, write the result to a stage-discharge file(.STG), and draw the graph into the CAD graphic. When you click on the Draw button, the Stage-Discharge Curve Settings dialog displays from where you can define how to plot the text and graph on screen.
 |
| Stage-Discharge Limits |
 |
| Stage-Discharge Dialog |
Click on Generate Report button, the program will present a report screen that contains detailed information regarding the design parameters and the calculations. The report window provides the options of printing, drawing the report in AutoCAD or storing the report to a file. Shown below is an example.
 |
| Culvert Report |
A rating table presents the discharge-headwater relationship in the tabular form. It can be displayed in a Microsoft spreadsheet or a standard report. Click on Generate Rating Table button to open Rating Limits dialog. In the Variant list, select the independent variable. The available variables are Discharge and Headwater. Enter data in the Minimum, Maximum and Increment boxes. Enter the Tailwater Elev and select the decimal setting from the Decimals list. When you finish entering data, click on OK button to calculate the rating table. A rating table example is shown below in the standard report format. The first column Discharge is an independent variable, and the other columns are computed variables.
 |
| Culvert Rating Table Limits |
 |
| Culvert Rating Table in Report
Format |
Generate Sedcad File button produces a file with a .CVT extension that can be used as one of the building blocks for the SedCad Program ( a third hydrology and sedementology stand-alone software package). The file is identical to what is produced within SedCad by its utilities program. Draw Pipe Detail button plots a fully annotated standard detail, with user-controlled inlet and outlet slope entries and scaling.
 |
| Draw Pipe Detail Settings |
Culvert Design dialog: Fill
in
values
Pulldown Menu Location: Structure > Pipe Culvert Design
Keyboard Command: culvert
Prerequisite: a culvert file
File Name: \lsp\cntr_grd16.arx