The Basics of Culvert and Inlet Design

Jerry D. Morrow, P.E.

Course Outline

• Definitions and symbols to be used
• Design criteria and engineering considerations for culvert design
• Coefficients and tables to be used in design
• Culvert Flow Controls and Equations that are used within hydraulic computer programs
• Design Procedures
• The manual use of inlet and outlet control nomographs
• The use of a personal computer system programs for inlet and outlet considerations
• The Design Procedure steps
• Hydraulic charts and performance curves for velocity and capacity with inlet or outlet
• control
• Culvert Design Example Using Nomographs
• Design of Improved Inlets with Inlet Control and Outlet Control
• Three examples are given:
• Example 1 - Reinforced Concrete Box Culvert Design
• Example 2 - Irregular Culvert Cross Section
• Example 3 - Multiple Independent Barrels
• Sample computer input and output for culverts and inlets
• Construction and Maintenance Considerations

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective

At the conclusion of this course, the student will learn:

• Primary considerations for the final selection of any drainage structure are that its design be based upon appropriate hydraulic principles, economy, and minimized effects on adjacent property by the resultant headwater depth and outlet velocity.
• Risk of property damage to adjacent property
• Construction and maintenance costs associated with sizing considerations
• Traffic safety regarding guardrail, culvert extension and slope to culvert headwall
• Environmental considerations
• Risk of failure from load, including dead-load, live load and impact loading
• Aesthetic considerations
• Uniform flow is flow in a prismatic channel of constant cross section having a constant discharge, velocity and depth of flow throughout the reach
• Free outlet design.  Free outlets  are outlets when tailwater is equal to or lower than critical depth
• Submerged inlet design.  Submerged inlets are inlets having a headwater greater than about one and one-half times the diameter of the culvert.
• Flared, improved, or tapered inlets design.  These are indicated by a special entrance condition which decreases the amount of energy needed to pass the flow through the inlet and thus increases the capacity of culverts at the inlet.
• Engineering aspects,  including flood frequency, velocity limitation and buoyancy protection
• Site criteria such as length and slope and debris control
• Design limitations , including Headwater, Tailwater conditions and Storage
• Design options for:

• Culvert inlets
• Inlets with headwalls
• Wingwalls and aprons
• Improved inlets
• Material selection
• Culvert skews
• Culvert sizes

• Designs considerations for:                         

• Weep holes
• Outlet protection
• Erosion and sediment control
• Environmental considerations
• Safety considerations

• Design of:
  • Culvert inlets
  • Inlets with headwalls
  • Wingwalls and aprons
  • Improved inlets
  • Material selection
  • Culvert skews
  • Culvert sizes
• Designs of related items including: 
  • Weep holes
  • Outlet protection
  • Erosion and sediment control
  • Environmental considerations
  • Safety considerations
• Consideration of storage capacity behind a roadway embankment attenuates a flood hydrograph. Because of the reduction of the peak discharge associated with this attenuation, the required capacity of the culvert, and its size, may be reduced.
• Design by nomograph (nomographs included)
• Typical hydraulic input and output from computer programs designed for PCs
• Construction and Maintenance Considerations.  An important step in the design process involves identifying whether special provisions are warranted to properly construct or maintain proposed facilities

Intended Audience

The intended audience should be engineers interested in the hydraulics of culverts and inlets and considerations of the factors affecting the design of these structures

Benefit to Attendees

Often computer programs are used for sizing, and design controls without understanding or remembering the engineering considerations of hydraulic design.  Hydraulic properties and hand analysis using equations and nomographs allow the designer to evaluate typical hydraulic considerations.

Course Introduction

The design of a culvert is influenced by cost, hydraulic efficiency, purpose, and the topography at the proposed culvert site. Thus physical data must be integrated with engineering and economic considerations. The information contained in this chapter should give the design engineer the ability to design culverts taking into account the factors that influence their design and selection.  While computer programs are often used for design, the input data requires knowledge what effects the data has and what conditions must be evaluated.  While most of the recommendations made herein are commonly accepted, they are the opinion of the writer and local standards will always prevail.

Course Content

This course content is in the following PDF document:

The Basics of Culvert and Inlet Design

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Course Summary

The design of a culvert is influenced by cost, hydraulic efficiency, purpose, and the topography at the proposed culvert site. Thus physical data must be integrated with engineering and economic considerations. The information contained in this chapter should give the design engineer the ability to design culverts taking into account the factors that influence their design and selection.  While computer programs are often used for design, the input data requires knowledge of what effects the data has and what conditions must be evaluated. 

Related Links and References

American Association of State Highway and Transportation Officials. Highway Drainage Guidelines. 1982.
Federal Highway Administration. Hydraulics of Bridge Waterways. Hydraulic Design Series No. 1. 1978.
Federal Highway Administration. Hydraulic Design of Highway Culverts. Hydraulic Design Series No. 5. 1985
Federal Highway Administration. Debris-Control Structures. Hydraulic Engineering Circular No. 9. 1971.
Federal Highway Administration. HY8 Culvert Analysis Microcomputer Program Applications Guide.
U. S. Department of Interior. 1983. Design of Small Canal Structures.

Quiz

Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.

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DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.

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