Storm overflows in England and Wales: understanding the controversy and challenges
In March 2024, the English water community unveiled a comprehensive plan to eliminate 150,000 annual sewage spills by 2030 through nearly 9,000 storm overflow improvements. If approved by Ofwat, this plan would implement the world's most significant storm overflow programme, ensuring all 14,187 overflows in England meet or exceed government targets.
Storm overflows, also known as Combined Sewer Overflows (CSOs), are critical components of England and Wales’s sewerage system. These structures act as relief valves during heavy rainfalls, releasing excess rainwater and wastewater into rivers or seas to prevent the sewer system from becoming overwhelmed. If the system becomes inundated, it can lead to severe flooding or even sewage backing up into homes, posing significant health risks and property damage.
These overflows are not a new concept; they have been a part of the infrastructure since before the 1960s. Despite being less environmentally harmful than other pollution sources, such as untreated sewage from treatment works or agricultural runoff, storm overflows still have substantial impacts on river and coastal ecosystems. There are currently over 14,000 storm overflows across England, and their role in managing wastewater has come under increasing scrutiny in the past years due to their environmental and aesthetic impacts.
Said this, the United Kingdom is not the only European country to have CSOs. Currently, Denmark, Belgium, The Netherlands and parts of Germany also use this type of infrastructure that acts as relief valves when the sewerage system is at risk of being overwhelmed. According to Water UK, the trade association for the UK water industry, England has a much lower number of CSOs than other countries with England and Wales achieving one hundred per cent monitoring at the end of 2023.
Addressing the causes and impacts of storm overflow use is a complex task involving various government bodies. The Department for Environment, Food and Rural Affairs (Defra) and the Welsh Government set the legislative and policy framework for wastewater management, which is then implemented by the Environment Agency in England and Natural Resources Wales in Wales. These agencies monitor water quality, issue permits for storm overflows, and take legal action against companies for permit breaches. Ofwat, the economic regulator, sets performance targets for water companies and can impose fines for non-compliance with license conditions.
Rising concerns over overuse
Ofwat has warned that public concern about storm overflows has heightened, particularly over their operation during periods of insignificant rainfall. The resulting discharges can severely damage aquatic ecosystems and make rivers and beaches less enjoyable for recreation. Additionally, the presence of sewage in these water bodies erodes public trust in water companies.
Despite being less environmentally harmful than other pollution sources, storm overflows have substantial impacts on river and coastal ecosystems
The efforts to reduce storm overflow spills are further complicated by climate change, population growth, and urbanisation. Climate change is expected to bring more intense rainfall, exacerbating the frequency and impact of storm overflows. Additionally, urbanisation increases the amount of impervious surfaces, such as roads and buildings, which prevents rainwater from being absorbed into the ground. This leads to higher volumes of runoff entering the sewer system, further stressing the infrastructure. Over the last 25 years, urban land cover has increased by 30 per cent and suburban cover by 40 per cent.
Despite the problematic aspects of CSOs, Water UK argues that the complete removal of storm overflows would require constructing a new parallel sewer network at an estimated cost of up to £600 billion, significantly increasing household bills and causing extensive disruption due to roadworks and construction. However, the association argues that upgrading and modernizing the existing sewer network can substantially reduce the frequency and impact of overflow events.
The National Storm Overflow Plan
In October 2023, water companies in England and Wales, through Water UK, proposed an unprecedented £96 billion investment to secure the country’s water supplies and upgrade its sewage systems. This proposal, if approved by the regulator, would nearly double annual investment in water infrastructure, making it one of the largest investments in Europe. The plan includes ambitious goals including that water companies will reduce water leaks by 28% over the next decade and facilitate the construction of ten new reservoirs. The investment will also fund the installation of advanced technology at sewage works to remove more pollutants before they reach waterways, such as preventing 800,000 tonnes of phosphorus from entering rivers and causing harmful algae blooms.
More significantly, the plan includes more than £10 billion specifically earmarked for storm overflow improvements, triple the current level of investment. If approved by Ofwat, the plan would implement the most extensive storm overflow programme globally, ensuring all 14,187 overflows in England meet or exceed government targets.
This initiative aims to eliminate more than 150,000 spills annually by 2030, with the number exceeding 325,000 by 2050. Throughout the plan's duration, over 4 million spills into rivers and seas would be prevented.
The plan targets a nearly two-thirds reduction in spills near bathing areas by 2030 and an approximate 80% reduction by 2050. In certain regions, the decrease would be even more substantial: for instance, Barnstaple Bay is projected to achieve over a 90 per cent reduction in spills by 2030, while North Cornwall is expected to see an 83 per cent reduction.
Projects that are revolutionizing storm overflow spills
While the National Storm Overflow Plan is under revision by Ofwat, English and Welsh water companies continue to propose new infrastructure and ways to tackle storm overflows, with three groundbreaking projects that highlight the innovative approaches being taken to manage storm overflows, from disruptive infrastructure, digitalization and nature-based solutions.
Thames Water’s Thames Tideway Tunnel
The Thames Tideway Tunnel, known as the London "super sewer," is among Europe’s largest infrastructure projects, set to complete in 2024 and start operations in 2025. Alongside the £700 million Lee Tunnel, it will capture 95% of untreated sewage entering the tidal Thames. This £4.5 billion project, delivered by Tideway, features a 25 km tunnel running from west to east London, largely beneath the River Thames.
Measuring 7.2 m in width and up to 67 m in depth, the tunnel can accommodate three London buses side-by-side, providing significant capacity to manage the growing population and environmental needs. Part of a three-part London Tideway scheme to improve river health, the tunnel aims to reduce sewage pollution in central London's River Thames drastically.
The Thames Tideway Tunnel, known as the London "super sewer," is among Europe’s largest infrastructure projects, set to complete in 2024
By the end of March 2024, Tideway announced the completion of the tunnel and its shafts, marking a major milestone with the placement of a 1,200-tonne concrete lid in Stratford. The project includes a 25 km main tunnel, a 4.5 km connection tunnel in south-east London, and a 1.1 km tunnel in south-west London. Once operational, this infrastructure will nearly eliminate tens of millions of tonnes of storm sewage spills into the Thames annually, significantly improving river health.
Northumbrian’s groundbreaking £20 million project
In June 2024, Northumbrian Water announced it had launched an innovative £20 million project aimed at significantly reducing storm overflow spills across Tyneside. This pioneering initiative, the first of its kind in the UK, integrates new technology, sensors, and AI analytics to minimize overflow risks. Inspired by successful methods used in South Bend, Indiana, the project aims to replicate the 80% reduction in spills achieved over a decade there.
The “smart sewer” project by Northumbrian Water will revolutionize wastewater management by altering the flow and direction of wastewater. This includes a mix of sewage, rainwater, road runoff, and domestic water, thereby reducing the likelihood of spills.
The “smart sewer” project by Northumbrian Water will revolutionize wastewater management by altering the flow and direction of wastewater
Employing AI technology and numerous smart sensors along sewer pipes, the system will predict and manage potential overflows by anticipating rainfall and network capacity, ensuring a more efficient and responsive sewer system.
Southern Water’s use of wetlands
Southern Water has announced a £35 million investment to reduce storm overflows by March 2025. This initiative focuses on at least 30 storm overflows, aiming to cut annual discharges by at least 420 within the next two years.
The utility is utilizing wetlands at its treatment works to provide additional storage and slow the flow of water into the network. Southern Water plans to construct four wetlands before spring 2025, with one already operational in Lavant.
Economic considerations and public impact
Funding these critical investments will result in incremental increases to water bills over a five-year period, states Water UK. By 2025, the average bill in England is expected to rise by £7 per month, with a further increase to £13 per month by 2030. Recognizing the economic strain on households, water companies have committed to doubling the number of households eligible for financial support, reaching 3.2 million homes.
This record investment builds on the £200 billion already spent on the water system over the past three decades, which has significantly improved drinking water quality and reduced pollution from sewage works. The new investment aims to transform storm overflow management, ensuring sustainable and safe water resources for future generations.
Water UK’s Chief Executive David Henderson said: “While increasing bills is never welcome, this investment in our country’s infrastructure is essential to ensure the security of our water supply. Water companies are seeking regulatory approval to reduce overflow spills into rivers and seas as fast as possible and to doubling the number of households receiving support to pay their bills."
Future developments and policy needs
The success of the National Storm Overflow Plan hinges on regulatory approval and effective implementation. Ofwat, the regulator, is expected to provide its first decisions, known as a “draft determination”, by June 2024, with final decisions by December 2024. These determinations will shape the investment landscape for 2025-2030.