Skip to main content

CIRIA Culvert, screen and outfall manual - meet the authors

This month, we catch up with Jeremy Benn and Amanda Kitchen, JBA Consulting and authors of C786 guidance + CIRIA trainers to discuss CIRIA's guidance on which Culverts training is based.

Q: Has anything changed since C786 Culvert, screen and outfall manual was published in 2019?
Amanda: There is an increasing focus on sustainability and carbon reduction in line with the UN sustainable development goals. It’s recognised that the whole-life operational carbon associated with the inspection and cleaning of screens could be reduced, for example, by removing unnecessary screens or increasing bar spacing to trap less small debris, enlarging existing screens or installing automated screens to reduce the number of visits.  Data, methods and guidance are evolving all the time.#

Q: How has practice changed since C786 was published?
Amanda: We’ve seen a step change in the use of risk-based approaches to culvert and screen provision.  In the past, debris and security screens were sometimes installed at culverts without a rigorous assessment of need or potential impacts.  The manual provides guidance on assessing the need to restrict entry into a culvert for safety reasons or to reduce the risk of debris blockage, as well as alternatives to screening.  It includes two spreadsheet appendices which can be used to identify and assess risk factors and support the decision to screen (or not).  These have support decision-making at hundreds of screens throughout the UK over the last few years.  The tools are free to download from the CIRIA bookshop (

Q: What would you differently if the manual was written today?
Amanda: The current manual is a merger of three manuals and uses the structure of the CIRIA Culvert Design and Operation Guide, 2010. That guide did not have outfalls, screens and culverts as separate sections as it encouraged looking at the assets as an integrated system.  If C786 was to be updated, I think a section on general principles followed by separate sections for the three asset types would better reflect how most readers use it.

Q: How do you share emerging good practice?
Jeremy: CIRIA's Culvert, screen and outfall training course provides an opportunity to share some emerging good practice.  However, if knowledge, experience or lessons from case studies reach a critical mass and if the industry identifies a need for new or updated guidance, CIRIA would scope the update of the existing guidance. CIRIA's research is guided and reviewed by an industry-wide project steering group - their breadth and depth of knowledge and experience is invaluable.

Q. What has been the most memorable culvert or screen project?
Jeremy: enlarging masonry Victorian culverts in Todmorden to increase conveyance of both flow and bedload. This was achieved by underpinning. In 1982 these culverts had been significantly blocked by waterborne cobbles and gravel brought down by the river. Inspecting the culverts some 20 years later after a significant high flow event I was pleased to find only one single cobble in the culvert (which I removed!).
Amanda: crawling commando-style along an inverted syphon beneath a canal to inspect a new concrete lining – it was a squeeze but thankfully de-watered!
Q: What is your top tip for culvert or screen designers?
Jeremy: always make sure that the assumed tailwater depth is appropriate.
Amanda: understand the basic principles and know how to do a quick hand calculation to sense check the results from computer software.


Find out more about CIRIA Culverts training or download a free copy of C786 Culvert, Screen and Outfalls manual.