9:30am - 1:00pm





Combined Sewer Overflows – from challenge to opportunity

Combined Sewer Overflows (CSOs) operate as a pressure valve in our sewerage sewer systems designed to protect properties from sewers that when overwhelmed by rainfall can cause sewage to back up into our streets and properties causing flooding. CSOs are used to spill excess sewage into watercourses and the bathing water. The environmental risks as a consequence of CSO spills are likely to grow as a result of urbanisation, climate change and the ageing of our sewerage infrastructure. CSO spills can be associated with poor quality rivers and bathing waters and have recently attracted public and media scrutiny and outrage.

Subsequently the government released a Stormwater Overflow Discharge Reduction Plan in August 2022 and approaches to reduce CSO spills are a key part of the Water Industry National Environment Programme (WINEP) and the first round of the Drainage and Wastewater Management Plans (DWMPs). The management of CSOs are going to be a key feature of the industry’s investment plans for years to come and are likely to be one of the most significant areas of future investment for the water industry. Approaches to managing CSO spills include optimisation of the sewer system, building additional storage, reducing the amount of rainfall entering the drainage system through approaches like retrofitting Sustainable Drainage and sewer separation. Effectively and sustainably tackling CSO spills will require collaboration between water companies, local authorities, highway authorities and those managing urban drainage, surface water infrastructure and our places and spaces.

Learning Outcomes:

Attendees will…

  • Gain a shared understanding of the purpose of CSOs both at the treatment works and in the network
  • Have a broad understanding of approaches to monitor and regulate CSO spills
  • Understand and describe some options for managing CSO spills and the benefits to be achieved
  • Appreciate collaborative approaches to planning and delivering solutions to manage CSO spills

This training is now full. Registration is closed.

Should you have any questions or enquiries regarding this training, please email learning@ciwem.org.

The first round of Learning Hubs have been released!

Our face-to-face learning hubs are hosted by CIWEM friends and our Urban Drainage Group. Discussions will take place in person alongside the virtual presentations, and if you're lucky, some of the presentations may even take place at your site.

Sponsor the Training

Here is your chance to sponsor the event as part of the CIWEM Urban Drainage Group annual Training day.
Click the links below to view more details on hosting a regional hub and sponsoring the training or follow this link for more information.


Thank you to our current Urban Drainage Group Training sponsors!
Your generous support helps us deliver valuable training to the industry and promote good practice.

Our Speakers

​​Additional speakers to be announced soon!​


Day 1 - Setting the Context

9.30 – 9.40 | Introduction to the training day
9.40 – 9.55 | Overview of CSOs in urban drainage and surface water management, Elliot Gill, Stantec
9.55 – 10.10 | CSO performance and data, Steve Kenny, United Utilities
10.10 – 10.30 | Group discussion and questions
10.30 – 11.00 | Report back, discussion and questions
11.00 – 11.20 | Break
11.20 – 11.40 | CSOs the regulatory context, Phil Hulme, Environment Agency & Sharon Forrester, Scottish Environment Protection Agency
11.40 – 11.55 |
Good practice to manage CSOs, Margaret Williams, Severn Trent Water
11.55 – 12.15 | Group discussion and questions
12.15 – 12.50 | Report back, discussion and questions for the morning
12.50 – 13.00 | Close

Day 2 - Design Examples

9.30 – 9.40 | Introduction to the training day
9.40 – 10.00 | CSO design examples – setting the challenge
10.00 – 10.15 | Q&A
10.15 – 10.45 | Group working on examples
10.45 – 11.05 | Report back, discussion and questions
11.05 – 11.25 | Break
11.25 – 11.35 | CSO coastal design examples – setting the challenge
11.35 – 11.45 | Q&A
11.45 – 12.10 | Group working on example
12.10 – 12.30 | Report back, discussion and questions
12.30 – 13.00 | Discussion and questions
13.00 | Close

Delivery of the training days will be through a mixture of sponsored regional, in-person hubs and online using zoom.

Locations of regional in-person hubs will be announced soon.

If you have any queries about this event, please contact our Learning & Development team at learning@ciwem.org.

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