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Cover of Guide to Road Design Part 5B: Drainage-Open Channels, Culverts and Floodway Crossings
Guide to Road Design Part 5B: Drainage-Open Channels, Culverts and Floodway Crossings
  • Publication no: AGRD05B-23
  • ISBN: 978-1-922700-77-3
  • Published: 30 January 2023
  • Edition: 1.2

Guide to Road Design Part 5B: Drainage – Open Channels, Culverts and Floodway Crosings contains guidance on the design of open channels, culverts and floodways to support the operation and management of the road network.

This Guide needs to be used in conjunction with the other two Parts of the Guide to Road Design that relate to drainage design:

  • Guide to Road Design Part 5: Drainage -  General and Hydrology Considerations
  • Guide to Road Design Part 5A: Drainage - Road Surface, Network, Basins and Subsurface

This Guide provides guidance on the fundamentals of open channel, culvert and floodway flows, and includes methods to undertake the design of these drainage facilities.

The guide includes design processes and formula necessary to design effective drainage systems and infrastructure.  It is supported by appendices containing design charts and worked examples that provide further information.

This guide provides guidelines on good practice in relation to drainage design that will apply in most situations, rather than specifying mandatory practice.

In Edition 1.2, Sections 4.1, 4.2, 4.5, 4.6 and 4.7 have been rewritten. Also, the term ‘floodways’ has been changed to ‘floodway crossings’ throughout the document and the term RL (Reduced Level) has been replaced by Height.

In Edition 1.2, Sections 4.1, 4.2, 4.5, 4.6 and 4.7 have been rewritten. Also, the term ‘floodways’ has been changed to ‘floodway crossings’ throughout the document and the term RL (Reduced Level) has been replaced by Height.

  • Summary
  • 1. Introduction
    • 1.1 Purpose
    • 1.2 Scope of this Part
    • 1.3 Road Safety
  • 2. Open Drains and Channels
    • 2.1 Introduction
      • 2.1.1 Definition and Use
      • 2.1.2 Factors in Choice of Channel Type
      • 2.1.3 Environmental Consultation
      • 2.1.4 Types of Open Drains
    • 2.2 General Considerations
    • 2.3 Fundamentals of Open Channel Flow
      • 2.3.1 Stream Dynamics
      • 2.3.2 Assumptions for Analysis
      • 2.3.3 Fundamental Equations
      • 2.3.4 Application of Fundamental Equations
      • 2.3.5 Energy Principles
      • 2.3.6 Hydraulic Jump
      • 2.3.7 Hydraulic Drop
    • 2.4 Erosive Velocities in Natural Streams
    • 2.5 Backwater
      • 2.5.1 Tidal Waters
      • 2.5.2 Downstream Tributary
    • 2.6 Tailwater Heights
      • 2.6.1 Tailwater Effects
      • 2.6.2 Design Tailwater Heights
    • 2.7 Open Channel Design
      • 2.7.1 Design Methodology
      • 2.7.2 Channel Transitions
      • 2.7.3 Energy Losses in Channel Bends
      • 2.7.4 Superelevation in Channel Bends
    • 2.8 Grassed Channels
      • 2.8.1 Normal Grassed Channels
      • 2.8.2 Reinforced Grassed Channels
    • 2.9 Channels Lined with Hard Facings
      • 2.9.1 General
      • 2.9.2 Riprap and Rock Filled Wire Mattresses/Gabions
      • 2.9.3 Concrete Lined Channels
    • 2.10 Channel Drops
      • 2.10.1 Check Dams
    • 2.11 Baffle Chutes
    • 2.12 Edge Drains and Median Drains
      • 2.12.1 Design of Edge and Median Drainage
    • 2.13 Table Drains and Table Drain Blocks
      • 2.13.1 Table Drains
      • 2.13.2 Table Drain Blocks
      • 2.13.3 Diversion Drains and Diversion Blocks
    • 2.14 Batter Drains and Chutes
      • 2.14.1 Design Procedures – Batter Drains
    • 2.15 Catch Drains and Catch Banks
      • 2.15.1 Catch Drains
      • 2.15.2 Catch Banks
      • 2.15.3 Design Procedures – Catch Drains and Catch Banks
    • 2.16 Worked Examples
      • 2.16.1 Example 1: Manning’s Equation – Determine the Flow Rate, Velocity and State of
      • 2.16.2 Example 2: Manning’s Equation – Determine the Depth and Velocity of Flow
      • 2.16.3 Example 3: Manning’s Equation: Determine the Flow Rate and Average Velocity in a Compound
      • 2.16.4 Example 4: Hard-lined/Rigid Boundary Channel Design
      • 2.16.5 Example 5: Vegetated/Erodible Boundary Channel Design
  • 3. Culverts
    • 3.1 Introduction
    • 3.2 Information Required
    • 3.3 Culvert Location
      • 3.3.1 Horizontal Alignment
      • 3.3.2 Vertical Profile
      • 3.3.3 Non-hydraulic Considerations
    • 3.4 Culvert Type
      • 3.4.1 Culvert Shape
      • 3.4.2 Materials
    • 3.5 Culvert Size
      • 3.5.1 Minimum Culvert Size Allowable
      • 3.5.2 Other Sizing Considerations
    • 3.6 Structural Requirements
      • 3.6.1 Design Loads
      • 3.6.2 Existing Culverts
      • 3.6.3 Space between Pipes in Multiple–Barrel Culverts
      • 3.6.4 Cover
    • 3.7 Hydraulic Design Considerations
      • 3.7.1 Design Discharge
      • 3.7.2 Outlet Velocity
      • 3.7.3 Culverts in Flat Terrain
      • 3.7.4 Siltation and Blockage
      • 3.7.5 Allowable Headwater (AHW)
      • 3.7.6 Tailwater (TW)
    • 3.8 Typical Culvert Operating Conditions
      • 3.8.1 General
      • 3.8.2 Inlet Control Conditions
      • 3.8.3 Outlet Control Conditions
    • 3.9 Hydraulic Calculations
      • 3.9.1 Control at Outlet
      • 3.9.2 Determination of Tailwater
    • 3.10 Design Procedures
      • 3.10.1 Hydraulic Design
      • 3.10.2 Collect Design Data
      • 3.10.3 Select a Trial Culvert
      • 3.10.4 Design Discharge for Trials
      • 3.10.5 Determine Inlet Control Headwater Depth
      • 3.10.6 Determine Outlet Control Headwater Depth
      • 3.10.7 Determine the Controlling Headwater
      • 3.10.8 Outlet Velocity – Outlet Control
      • 3.10.9 Outlet Velocity – Inlet Control
      • 3.10.10 Outlet Flow Energy
      • 3.10.11 Design Check
      • 3.10.12 Practical Design
    • 3.11 Blockage of Culverts
    • 3.12 Consideration of Large or Extreme Events
    • 3.13 Culvert Outlet Protection
    • 3.14 Culvert End Treatments
      • 3.14.1 General
      • 3.14.2 Slope Faced
      • 3.14.3 Traversable Endwalls
    • 3.15 Worked Examples
      • 3.15.1 Example 1: Application of Culvert Design Procedure
      • 3.15.2 Example 2: Culvert Outlet Protection
  • 4. Floodway Crossings
    • 4.1 Introduction
      • 4.1.1 Design Parameters/Criteria
    • 4.2 Design Considerations
      • 4.2.1 General
      • 4.2.2 Culvert Dimensions and Design Considerations for Culverts under the Floodway
      • 4.2.3 General Safety
      • 4.2.4 Sight Distance
      • 4.2.5 Horizontal Alignment
      • 4.2.6 Vertical Alignment
      • 4.2.7 Cross Section
      • 4.2.8 Signage
      • 4.2.9 Environmental Considerations
      • 4.2.10 Hydraulic Flow Considerations
    • 4.3 Hydraulic Design
      • 4.3.1 Flow Over the Road
      • 4.3.2 Full Floodway Crossing Calculations
    • 4.4 Time of Submergence and Closure
      • 4.4.1 Introduction
      • 4.4.2 Calculating of Time of Submergence and Closure
      • 4.4.3 Time Required to Reopen the Road after Flood Closures
      • 4.4.4 Costs of Flood Closures
    • 4.5 Flood Damage
      • 4.5.1 Flood Damage Examples
    • 4.6 Floodway Crossing Profiles
      • 4.6.1 Introduction
      • 4.6.2 Types of Profiles
    • 4.7 Floodway Crossing Protection Examples
      • 4.7.1 Introduction
      • 4.7.2 Type 1 Floodway Crossing Protection – RC Margin, Batter and Apron
      • 4.7.3 Type 2 Floodway Crossing Protection – RC Margin and Batter with No Apron
      • 4.7.4 Type 3 Floodway Crossing Protection – RC Margin and Batter with Dished Apron
      • 4.7.5 Type 4 Floodway Crossing Protection – Stone Mattresses and Gabions
      • 4.7.6 Type 5 Floodway Crossing Protection – Bituminous Seal
      • 4.7.7 Type 6 Floodway Crossing Protection – Dumped Riprap
      • 4.7.8 Grass Batters
    • 4.8 Worked Examples
      • 4.8.1 Example 1: Floodway Crossing Design
      • 4.8.2 Example 2: Floodway Crossing Design
  • References
  • Appendix A Vegetal Retardance Curves
  • Appendix B Inlet and Outlet Control Nomographs
    • B.1 General
    • B.2 Inlet Control
    • B.3 Outlet Control
  • Appendix C Velocity and Critical Depth
    • C.1 General
  • Appendix D Culvert Capacity
    • D.1 Introduction
    • D.1.1 Socket End of Spigot and Socket Pipes
    • D.1.2 Socket End of Spigot and Socket Pipes
    • D.1.3 Flush Jointed Pipes
    • D.1.4 Concrete Box Culverts
  • Appendix E Solving Manning’s Equation
    • E.1 Introduction
    • E.1.1 Application 1
    • E.1.2 Application 2
    • E.1.3 Application 3
Related publications
Guide to Road Design Part 5: Drainage-General and Hydrology Considerations
AGRD05-23
Guide to Road Design Part 5A: Drainage: Road Surface, Networks, Basins and Subsurface
AGRD05A-23
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