Sewer overflows are the release valves for the sewerage system. When sewage treatment works cannot keep up with the amount of sewage entering them, the raw untreated sewage is discharged via sewer overflows into the nearest river. In theory, these overflows are only used during heavy rainfall when rainwater entering combined sewers cause the treatment works to be overloaded; during these periods the overflow should therefore contain mostly rainwater. 

Unfortunately, storm overflows are being used regularly, including in the Dee catchment where raw sewage was discharged 8,368 times in 2021. As the frequency of raw sewage discharges has come to light, public outrage has led to a flurry of new policies, plans and commitments by government and water companies to tackle the issue. The public sewerage system discharging into the Dee is managed by Dwr Cymru, but it is impacted by regulations from both England and Wales as the river is a cross-border catchment.   

Historically, the legislation covering storm overflows is covered by the Urban Wastewater Directive, which requires sewage from towns larger than 2000 individuals to be collected and treated, and The Water Industry Act of 1991 which includes section 94, ‘to provide, improve and extend a system of public sewers to treat sewage effectually’. Arguably these pieces of legislation have been broken by the excessive use of combined sewer overflows and the Environment Agency and Ofwat launched an investigation into water companies in 2021. Currently, six water companies are identified in enforcement cases as part of this investigation. Dwr Cymru is not one of the companies.  

In Wales, the Senedd set up the Wales Better River Quality Taskforce. The taskforce published an ‘environmental regulation of overflows: action plan’ in July 2022. This plan includes a requirement to set achievable long, medium and short-term targets for the prevention of ecological harm from overflows. The plan sets out a deadline of March 2023 for the setting of these targets.  

Additional action plans published by the taskforce set out a variety of other targets both ongoing and with deadlines. Targets of note are:  

• By 2025 Dwr Cymru has committed to a system which will report all overflow discharges within an hour.  
• Install screens on 100% of storm overflows by 2050. 
• Dwr Cymru has committed to a full assessment of the impact of all storm overflows by December 2027.  

The full list of actions can be seen here.

In England, the 2021 Environment Act set out government plans to conserve and enhance biodiversity including water quality. The Environment Bill did not include the Duke of Wellington’s amendment to place a ‘duty on sewerage undertakers to make progressive reductions in the harm caused by discharges of untreated sewage’. The amendment was voted down by the House of Commons, leading to many Members of Parliament being accused of voting to allow water companies to discharge sewage to rivers. The Westminster government did replace the amendment with its own weaker amendment. Full details comparing the two amendments can be seen here.

The newly amended Environment Bill did place a duty on the government to produce a statutory plan to reduce discharges from storm overflows. This plan was released in August 2022. The plan sets the targets for the Westminster government’s pathway for reducing the impact of storm overflows in England. The main targets include:   

• Water companies can only discharge from a storm overflow when they can demonstrate no local adverse ecological impact, they must achieve this for 75% of discharges near high-priority sites by 2035 and 100% by 2045. All remaining discharges must achieve this target by 2050. 
• Storm overflows cannot discharge above an average of 10 rainfall events per year by 2050.  

Other targets include requirements for water companies to deliver drainage and wastewater management plans, improve monitoring and reporting on overflows and improve screens on overflows. Both Wildfish and the Marine Conservation Society have been permitted a hearing by the High Court to apply for a judicial review of the action plan.  

At Welsh Dee Trust we are pleased new legislation is being enacted to reduce the frequency and ecological impact of sewer overflows but feel the current targets are not robust or acting fast enough. We also believe the Westminster government’s discharge reduction plan risks allowing harmful impacts to continue until 2050 when stricter regulations are already in place, and fully support Wildfish and the Marine Conservation Society’s goal of a judicial review. We will also be watching with interest the targets set by the Welsh Government in March and feeding in via Afonydd Cymru any targets we feel need to be strengthened. The first Dwr Cymru drainage management plan will be released in 2023 which we hope will set clear investment strategies to reduce sewer overflows into the Dee.  

Our focus remains on identifying pollution incidents on the ground and working to fix them. Over the next five years, our ‘It Shouldn’t be in the Dee’ programme will train 100 citizen scientists, whom we will support to identify sources of pollution, including sewer overflows, and improve 150 drains across the Dee catchment to reduce pollution. If you want to help us, please sign up to become a volunteer or train to become one of our citizen scientists.