Big question

BQ6 - How do we achieve zero uncontrolled discharges from sewers by 2050?



We are currently working on the approach to answering this Big Question, and more information will be given here soon.

The areas that this Big Question covers includes:

  • Reduce sewer blockages
  • Reduce overflows (escapes) at rising mains and pumping stations
  • Achieve integrated sewerage catchment management
  • Address sewer infiltration, excess surface water flows including flows from developments
  • Play our part in wider flood management
  • Support the industry’s 21st Century Drainage programme of work

Once we understand where the gaps are, we will produce a route map – this is a plan as to how we will answer our Big Question.

The route map will have a number of key elements. At the top will be our Big Question and then we will look to see what Outcomes we need from the research programme -if we can achieve all these outcomes we can answer the Big Question. This is the stage we are currently at for this Big Question.

The next stage will be to think about the key benefits we want the research projects to deliver to meet these outcomes.

Following this, we will plan the research projects to help deliver the benefits.


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BQ06 - Quantifying, managing and communicating the differences in storm overflow spill data between EDM outputs and Hydraulic Model predictions.

Project Status - Project Commenced

There is evidence that measured EDM outputs (frequency and duration of discharges from storm overflows) can often contrast against modelled spill outputs used for strategic planning and options development through the DWMP and WINEP programmes.

With greater coverage of sewer modelling and EDM, it is key to understand how the datasets compliment each other and can be used for planning such as through DWMPs as well as to  better understand and address performance and communicate to stakeholders and customers.

This need for this research project has been identified by the industry through the DWMP process, WINEP SOAF planning and also through the CIWEM UDG.  

Reasons for differing data could include a mix of model / measurement tolerances, yearly rainfall variation and counting methodology. 

The impact of the new monitoring requirement in the Environment Act on counting methodologies also needs to be understood.  


BQ06 - Treatment Options for Storm Overflows.

Project Status - Project Commenced

In order to deliver the required improvements to progressively reduce the adverse impact of storm overflows as detailed in the Environment Act, opportunities to treat overflows need to be further explored including their application, costs and benefits.  

Projects coming soon.

Projects coming soon.

Projects coming soon.


BQ06 B04 - Modelling Sewer Inlet Capacity Restrictions.

Project Status - Project Commenced

Develop a methodology to better represent how inlet restrictions are embodied within sewer modelling to improve our understanding of flood risk during severe rainfall events.


BQ06 Understand the long term costs and wider benefits of Surface Water removal and SuDS to tackle sewer flooding and storm overflow operation.

Project Status - Project Commenced

To tackle storm overflows and sewer flooding, the removal of surface water from the combined sewer system via SuDS represents a potentially more sustainable alternative to traditional grey infrastructure and has the potential to deliver wider benefits to the environment and society including longer term flood resilience. 

Initial costs and benefits appraisals (including carbon estimates) for SuDS through the Storm Overflow Evidence Project and Drainage and Wastewater Management Plans have indicated however that SuDS could be potentially higher in both cost and carbon. 

Because there are relatively few examples of the whole life costs and benefits of retro-fitted SuDS delivered by the Water Industry this research aims to further develop our understanding of the initial capital costs, long term opex costs,  and whole life benefits. 
It will also deliver tools that can be used for planning purposes and to influence regulation and policy. 


BQ06-A4a - Understanding the scale and impact of privately owned drains/sewers on sewer capacity.

Project Status - Project Completed

Category - Sewerage

Leakage in domestic supply pipes is a significant contributor to the total leakage reported each year. However, the equivalent on the wastewater side of the business – infiltration into privately owned pipes and manholes – remains totally unquantified.

This is firstly because the total length of privately owned drains/sewers is unknown and never been estimated. Secondly, the extent as to which they allow groundwater ingress is also totally unknown.

The consequence of privately owned pipes and manholes that allow groundwater ingress is that they are thought to be major contributors to the number and hours of storm overflow operation. This is especially prevalent in chalk strata, where high groundwater tables are experienced and where the impact of storm overflow discharges to chalk streams, which can last for months, can be significant. 

In water supply, statutory undertakers have the ability to enforce the fixing of leaks on domestically owned pipes by serving notice under S75 of the Water Industry Act.

No equivalent powers exist on wastewater infrastructure.

Private pipe sealing can be carried out with permission of the owner and at the cost of the sewerage undertaker but only Local Authorities have powers to require owners of buildings to carry out remedial works on drains which are defective and let sub-soil water in (Section 59 of the Public Health Act). They also have powers to repair drains which are not sufficiently maintained and recover costs (up to £250) from the owner (Section 17 of the Public Health Act). However, they have no motivation to do this as the consequence has no impact on the LA.

In order for more informed consideration about how private pipes that allow infiltration should be rectified, it is important to first establish the approximate length of privately owned drains and sewers. By inspection, this length of pipework will be longer than the length of publicly owned sewers and lateral drains, but no evidence exists for this supposition – hence the need for the project.


Infiltration detection.

Project Status - Project Completed

Category - Sewerage

There are several methods recognised to detect infiltration (CCTV, Electroscan etc) but all appear to have shortcomings that prevent them being as effective as is needed. Infiltration seems to be an intractable problem for several companies in the south of England (and others to a lesser extent) and can only be remedied where measurable (short of wholesale replacement/relining).

This suggestion is to engage with universities/academia to suggest and pilot alternative technologies