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Environment Waikato Best Practice Guidelines for Waterway Crossings

Report: TR 2006/25R
Authors: David Speirs, Greg Ryan


These best practice guidelines have been prepared to assist regional and local authorities, consultants, roading engineers and contractors with the design of appropriate waterway crossings within the Waikato region. By following the recommendations in this handbook, proposed waterway crossings:

  • will be designed to have the minimum possible adverse impact on the environment
  • will be consistent with the requirements of the Waikato Regional Plan.
  • will not compromise the levels of service provided by regional and district flood protection or land drainage schemes.

The topics covered by this best practice guideline handbook include:

  • the Waikato Regional Plan
  • flood control schemes and land drainage areas
  • best practice design guidelines for waterway crossings.

Environment Waikato Best Practice Guidelines for Waterway Crossings
(1168 kb, 166 seconds to download, 56k modem)

Table of Contents

1 Introduction 1
1.1 What is best practice? 1
2 The Waikato Regional Plan 1
3 Flood control schemes and land drainage areas 2
4 Type of waterway crossings 2
4.1 Single span bridge 2
4.2 Single barrel arch culvert 3
4.3 Multiple span bridge 5
4.4 Single barrel circular culvert 5
4.5 Multi-barrel circular culvert 7
4.6 Box culverts 8
4.7 Fords 8
5 Maintaining & restoring ecological values 9
5.1 Design and construction considerations 10
5.1.1 Water velocity 11
5.1.2 Crossing inlet conditions (culverts) 12
5.1.3 Physical barrier to aquatic invertebrates 13
5.1.4 Flow turbulence 13
5.1.5 Light requirements 14
5.1.6 Water depth and wetted margin 14
5.1.7 Perched culverts 15
5.1.8 Timing of works 16
5.1.9 Structure location and stream alignment 16
6 Designing waterway crossings for flood events 17
6.1 Definition of a reasonable flood event or design standard 17
6.2 Estimation of design peak flood flow 17
6.2.1 Define the waterway catchment 18
6.2.2 Calculate the average slope of the main waterway 19
6.2.3 Calculate the time of concentration for the catchment 20
6.2.4 Define the design storm for the proposed crossing 20
6.2.5 Calculate the design peak flood flow for the proposed crossing 20
6.3 Design strategies using the design peak flood flow 21
6.3.1 Bridges 21
6.3.2 Culverts 22
6.3.3 Fords 23
7 Conclusion 23
8 Recommended reading 23
Appendix 1 Contacts-territorial authorities 25
Appendix 2 Useful equations 26
Appendix 3 Average slope worksheet 29
Appendix 4 Technical memorandum 61 work sheet 30
Appendix 5 Associated hazards table 31


Note: This report was originally published in May 2006 as Technical Report 2006/25. This new edition corrects a minor data error which appeared in Appendix 2, on the first line of page 27. The word ‘minutes’ was accidentally substituted instead of ‘hours’ in a ‘time of concentration formula’. While addressing this error, the opportunity was taken to make some other minor typographical changes. These changes make no difference to the conclusions or recommendations in the report, but in the interests of data accuracy we are re-releasing this publication.

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