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

Project Status - Project Commenced

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.


Climate Change Rainfall for use in Sewerage Design - Design Storm Profiles, Antecedent Conditions, RedUp Tool Update and Seasonality Impacts.

Project Status - Project Completed

Category - Stormwaters

Following on from the release of UKCP18 and the work of the FUTURE-DRAINAGE project, being led by Newcastle University, JBA Consulting and Loughborough University, there is a need to convert some of the learning and outputs into usable design tools and information for the industry. In particular, the industry needs to update the RED-UP tool, which is used in the perturbation of Time Series Rainfall, to the latest climate change forecasts, which is an integral part of the Drainage & Wastewater Management Planning (DWMP) process.

In association with this, the industry has not reviewed the shape of design rainfall events, which are typically split over summer and winter periods, following the latest climate change predictions. These design rainfall profiles are used across the water industry in assessing existing and future performance of systems and designing new schemes and interventions. These design storm profiles, date back to the Flood Studies Report, published in 1975, and therefore are in need of validation or correction with the latest information. The application of these design rainfall profiles also needs to be considered to which seasons they are most appropriate and applicable to, especially given the forecast climate change impacts for the autumn period.

Linked to these, the industry needs a review, and subsequent guidance produced, on the antecedent conditions that are used in running design rainfall models, such as the NAPI/API30 values as well as the changes to evaporation and evapotranspiration. Also, the Areal Reduction Factors associated with the improved understanding of climate change need to be reviewed.

The above outputs/elements of research need to align to current and future planning horizons to link into future DWMP reviews.


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