Culvert, screens and outfall manual
Producing a guide for the design, operation and management of culverts, trash screens and outfalls.
Documents
The outputs of this project were published by the Construction Industry Research and Information Association (CIRIA) in December 2019. To access the manual visit the CIRIA project webpage.
Project summary
This page summarises outputs of a 2019 project during which the CIRIA, the Environment Agency’s Flood and Coastal Erosion Risk Management Research Programme and their professional partners, produced a manual for designing and managing culverts, screens, and outfalls.
This guide is complemented by the Blockage management guide.
Background
Within the UK, there are over one million culverts and outfalls, with thousands of them incorporating debris or security screens. Many of these are vital in allowing important infrastructure, such as railways, roads, and footpaths to safely cross watercourses, as well as enabling drainage systems to function safely.
At first glance, culverts, screens and outfalls can appear to be relatively simple structures, but they have the potential to completely restrict flow. They are often costly to maintain and being intrinsically linked to other infrastructure or urban environments, can adversely affect sensitive aquatic environments, and create severe health and safety hazards.
This project produced an efficient and responsible approach to managing flood risk from such assets.
Method
The project made use of developments in environmental science, engineering and hazard awareness across a range of industries to provide a single and definitive culvert, screen and outfall manual (CSOM) for users.
Combining and updating the Environment Agency’s trash and security screen guide from 2009 (TSSG), with CIRIA’s culvert design and operation guide from 2010 (CDOG) created a unique opportunity to make the most of the knowledge and experience held by the Environment Agency, CIRIA, and our network of mutual partners (Network Rail, Highways England, and Transport Scotland).
Results
The CSOM seeks to avoid the use of culverts and screens altogether. Where there are demonstrably no alternatives to culverting, the design principles in the CSOM helps designers to remove the need for screens, as well as reducing whole life costs to little more than routine inspection and maintenance.
The CSOM also provides decision and design support for the hundreds of thousands of existing culverts, screens, and outfalls across the UK. Within this existing stock, problems such as structural decay, inadequate capacity, sedimentation, and blockage risks mean ongoing assessment, rehabilitation, repair, and enhancement are often needed.
Increasing environmental and legal concerns also require asset managers to look at ways of improving the environmental, hydraulic and health/safety performance of these systems, as well as their operational performance.
Conclusion
The CSOM adopts an ‘evidence-based’, ‘whole life’ and ‘full system’ approach to the design and management of culverts, screens, and outfalls, with strong presumptions for restoring systems to a more natural state through ‘daylighting’ and against building screens or culverts – unless there are demonstrably no alternatives.
The CSOM presents a framework to assess, plan and manage these systems consistently and logically. It steers users through:
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testing the need for a structure and a screen
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planning and implementing appropriate designs
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understanding the legal framework
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carrying out hydrological and hydraulic analysis
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managing health and safety
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maximising links with the wider environment and natural processes
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deciding on repair, renovation and/or removal
Project Information
Project manager: Mark Whitling, Flood and Coastal Risk Management, Environment Agency.
Collaborators: Construction Industry Research and Information Association (CIRIA), Environment Agency, Highways England, Network Rail, Transport Scotland.
Research contractors: JBA Consulting and Mott Macdonald Group Ltd.
This project was commissioned by the Environment Agency’s FCRM Directorate, as part of the joint Flood and Coastal Erosion Risk Management Research and Development Programme.
Updates to this page
Last updated 20 May 2022 + show all updates
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Link to project outputs added under documents heading. Project summary added to webpage body. The project is marked as complete.
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First published.