HY-8:Concrete Open Bottom Arch
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HY-8 Version 7.3 and later has coefficients for computing inlet control depths for concrete open-bottom arch (commonly called Con/Span) culverts.
Con/Span culverts have unique geometric configurations, and several sizes and shapes are available. The exact coordinates used in HY-8 to compute areas and other geometric cross section parameters are available in this document. Since the culverts can be made to accommodate any required rise for a given span, HY-8 contains culvert geometry in 3-inch increments of rise.
Inlet Control Polynomial Coefficients
The polynomial coefficients used by HY-8 were derived from a study and document prepared by Don Chase at the University of Dayton, Ohio (1999). Dr. Chase determined a different set of coefficients for culverts with different span-to-rise ratios. Con/Span culverts with a 4:1 span-to-rise ratio performed better (resulted in a lower headwater) than culverts with a 2:1 span-to-rise ratio. Because of this, separate polynomial coefficients were determined for culverts with each of these span-to-rise ratios.
Dr. Chase's study determined the K, c, M, and Y NBS coefficients described in HDS-5, and these coefficients were fitted to a 5th degree polynomial equation so they can be used in HY-8.
In HY-8, the 2:1 coefficients are used if the span:rise ratio is less than or equal to 3:1 and the 4:1 coefficients are used if the span:rise ratio is greater than 3:1. If the culvert you are modeling has less than a 2:1 or greater than a 4:1 span-to-rise ratio, you will see a note in HY-8 saying that your culvert is outside of the tested span-to-rise ratios. Further testing may be required to account for these large or smaller span-to-rise ratios, but it is likely that your computed headwater will be higher than the observed headwater if your span:rise ratio is greater than 4:1 and your computed headwater will be less than that observed if the span:rise ratio is less than 2:1.
For information on the exact coefficients used and to view diagrams showing the different culvert wingwall configurations, see the help describing the HY-8 polynomial coefficients.
Introduction: Getting Started ·
Differences from DOS HY-8 ·
Building a Project: Locate Project · Culvert Crossing Data · Run Analysis · Report Generation
— Crossing Data —
General Data: Crossings · Discharge Data
Roadway Data: Roadway Profile
Tailwater Data: Channel Shape · Rating Curve · Constant Tailwater Elevation
Irregular Channel: Irregular Channel Error
— Culvert Data —
Culvert Data: Shapes · Material · Plastic Pipe Materials · Concrete Open Bottom Arch · South Dakota Concrete Box · Culvert Type · Broken Back Culverts · Inlet Configurations · Inlet Depression · Embedment Depth
Site Data: Culvert Invert Data · Embankment Toe Data
— Analysis —
General: Project Units · Roadway Overtopping
Headwater Computations: Inlet Control Computations: Polynomial Generation · Polynomial Coefficients · Outlet Control Computations: Exit Loss Options · Hydraulic Jump Calculations
Tables and Plots: Crossing Summary · Culvert Summary · Water Surface Profiles · Tapered Inlet · Customized · Controlling Plot Display Options
— Energy Dissipation —
Scour Hole Geometry
Internal Energy Dissipators: Increased Resistance in Box Culverts · Increased Resistance in Circular Culverts · Tumbling Flow in Box Culverts · Tumbling Flow in Circular Culverts · USBR Type IX Baffled Apron
External Dissipators: Drop Structures: Box Inlet Drop Structure · Straight Drop Structure · Stilling Basins: USBR Type III Stilling Basin · USBR Type IV Stilling Basin · Saint Anthony Falls (SAF Stilling Basin) · Streambed Level Structures: Colorado State University (CSU) Rigid Boundary Basin · Riprap Basin and Apron · Contra Costa Basin · Hook Basin · USBR Type VI Impact Basin