Some of the most historic towns and cities in central England are built around the magnificent River Avon and even the root of the word ‘avon’ means river.

Now the health of this iconic waterway is being given a boost with installation of a series of underground storage tanks across Bath, Bristol and Bradford-on-Avon. Some of the new infrastructure is already preventing discharges of untreated water into the river during heavy rainfall.

By boosting storage volumes, excess stormwater can be held back during downpours and only released back into the sewerage system when capacity is available for onward treatment. The water company for the region, Wessex Water, says it is committed to progressively eliminating storm overflows, which sometimes operate during intense rainfall.

“While overflows have always been a part of this country’s sewerage system, protecting homes and businesses from flooding if the network become overwhelmed, we’re committed to progressively reducing their use and eliminating the release of untreated wastewater,” says Wessex Water project manager Greg Andrews.

The River Avon flows south west and is a major tributary of the longest river in Great Britain, the Severn, which eventually empties into the Bristol Channel. As part of an overall five-year investment of more than £150 million, water service company Wessex Water will deliver 13 priority projects to tackle the overflows that discharge most frequently or carry most significant environmental impact before 2025.

Investigation and monitoring of combined sewage and stormwater overflows into the river has also been enhanced, along with increased sewer relining to help keep wastewater within the network and prevent it from infiltrating into groundwater, which can lead to flooding. In addition, a web-app that informs swimmers and other river users about water quality is being trialled in partnership with the Rivers Trust and the Environment Agency.

Going underground in Bradford-on-Avon

The most recent phase of the programme is a £2 million project to enhance the health of the Avon in west Wiltshire, which completed in Spring 2024. A large below-ground storage tank now lies at the centre of the market town of Bradford-on-Avon.

Sewers carry both foul water from people’s homes and rainwater to a nearby water recycling centre for treatment. The additional 160,000 litres of storage will reduce the times this combined system discharges to the river.

Such releases of highly diluted and screened sewage into rivers are permitted by the Environment Agency to prevent wastewater from backing-up in the network and putting homes at risk of internal flooding. The new tank will ensure the stored water is safely returned to the sewer system and onwards for treatment after any storm has receded, protecting the river too.

“We’re pleased to have completed construction work on time as part of our £3 million a month investment towards reducing the instances of storm overflows operating across our region,” said Wessex Water project manager Alex Aulds.

“The main construction work has been finished and while our teams will continue to commission and test the new system throughout the summer, we would like to thank local customers and businesses for their patience, co-operation and understanding while this work was carried out.”

Holding back the flow in Hanham

A similar £800,000 project has already completed in Hanham, a residential area of east Bristol, where a below-ground storage tank has been built under green space. The tank is buried more than five metres underground and hosts an additional 50,000 litres of water.

Once a storm has receded, the excess water is returned to the sewer system and continues its journey to the city’s water recycling centre at Avonmouth, where it is properly treated before being safely returned to the environment.

Flooding tackled at rugby ground

The car park of Bath RFC’s playing fields at Lambridge, in the east of the historic city, is the site of another stormwater storage tank. This £1.3 million project has developed infrastructure able to hold more than 170,000 litres of stormwater.

The tank gradually returns the water to the sewer system for onward travel to a water recycling centre to be treated and safely returned to the environment. It will help cut the number of automatic operations of this nearby storm overflow into the River Avon by around three-quarters.

Wessex Water worked closely with Bath RFC to ensure they could still use their ground during the construction work. The five-month project involved removing more than 800 tonnes of soil and completed in December 2023.

More Bath overflows reduced

A second project in Bath will see more than £650,000 invested to enhance storage capacity in the Fox Hill area. Teams moved on to the site in June 2024, to build the new tank, which will be capable of hosting nearly 100,000 litres of excess water.

The tank will prevent overflows from operating at the River Avon more than a kilometre away. Instead, the stormwater will be returned to the sewer once the weather has eased and piped onwards to a water recycling centre for treatment and safe return to the environment. A length of sewer and manholes will also be constructed as part of the project.

Wessex Water project manager Greg Andrews said, “Between now and 2025 we’re tackling the overflows in our region that have operated most frequently in the past and our work at Fox Hill is one of those 13 priority projects.’’

Snakes and slow worms protected at Saltford

Protected species are a priority during a riverside project next to Saltford Rowing Club, where nearly £1 million is being spent to dramatically reduce the automatic operation of a storm overflow along the Avon.

Wessex Water teamed up with Bath Spa University to relocate a population of reptiles, including slow worms and grass snakes, to the nearby campus.

Three turf-covered log piles will be created for brumation - or hibernation - of the creatures, which are protected in the UK under the Wildlife & Countryside Act. They are also priority species under the UK Post-2010 Biodiversity Framework, meaning that they cannot be deliberately killed or injured in any way.

Ecologist Freya McCarthy will supervise the students’ involvement in the relocation, as she explains, “School of Science students will be offered the unique opportunity to assist in the relocation and hibernacula creation, learning key facts about our dwindling reptile species, including their ecology, identification, handling techniques and creating suitable habitat to sustain and help the population grow.

“This collaboration will provide the students with the opportunity to experience practical conservation practices and help them to understand the key principles around how we protect and enhance our local wildlife.’’

Wessex Water project manager Andre Laranjeira said, “The new tank will be able to host 50,000 litres of water flows from combined sewers, which carry both foul water from home and businesses and rain runoff, during heavy storms.

“This water can later be returned to the sewer and pumped onwards to nearby Saltford Water Recycling Centre for treatment and safe return to the environment.”

The five-month project started in May 2024.

Ways Wessex is tackling storm overflows

These are just five of the 13 stormwater storage schemes Wessex Water is carrying out to tackle overflows into the River Avon, but the company is tackling storm overflows in other ways too, including upgrading sewage treatment and increasing capacity at 42 water recycling centres (WRCs).

Saltford WRC, which treats sewage and wastewater from Bath and the surrounding area, will undergois undergoing a £35 million upgrade. By boosting capacity, Wessex Water will be able to treat more than 800 litres/second of wastewater – a 40% increase on current flows – before it is safely returned to the environment.

The water company is also introducing more reedbeds and wetlands using natural, low-carbon water treatment processes that also boost habitat for wildlife. Investigation and monitoring of stormwater overflows is being beefed- up, and an extensive programme of sewer- relining is also continuing, to help keep wastewater within networks, and prevent infiltration of groundwater that can lead to flooding.

In a trial initiative in partnership with the Rivers Trust and the Environment Agency, better information on water quality – and even temperature - for river users is becoming more readily available. The pioneering investigation involves bathing waters at Warleigh Weir in Somerset, and could help outdoor swimmers.

An artificial intelligence (AI) based web-app that can show bacterial levels in the River Avon at half-hourly intervals is currently in development. Testing already shows that the algorithm developed by UnifAI Technologies is 90% accurate when compared to laboratory samples.

As well as bacteria levels, the app shows four other parameters that could be of interest to swimmers – temperature, water level, water flow and rainfall. The temperature parameter is based on Outdoor Swimming Society advice that water below 15 degrees can risk cold water shock.

The project has been carried out by Wessex Water, supported by the Rivers Trust, Environment Agency and landowner Johnny Palmer. The web-app shows data collected by sensors at sample points at Warleigh and Monkton Combe since April 2021.

Ruth Barden, Wessex Water’s director of environmental solutions says, "This web-app is potentially a major breakthrough, giving people near real-time information about river water before they decide whether or not to swim. Bacteria will always be present in rivers due to wildlife, runoff from agricultural land, regulated storm overflows and treated sewage discharges, but we want to help the increasing number of wild swimmers and recreational river users make an informed choice."

Wessex Water already provides information for local councils, Surfers Against Sewage and others when storm overflows operate that could potentially affect coastal bathing waters and inland swimming sites.

Wessex Water chief executive Colin Skellett said, “We fully understand the public concerns about river health and, in particular, storm overflows; and we are committed to doing more, doing it faster, and transparently reporting progress.

“Storm overflows are the legacy of over 100 years, when sewerage systems were built using the same pipe to carry both sewage and rainwater, with overflows designed to protect property from flooding during very heavy rain. Unfortunately, there are no quick fixes; solving this problem will take many years of sustained effort and investment.

“It is also vital that the solutions we employ stand the test of time, against a background of climate emergency and changing rainfall patterns. So wherever possible we will use nature-based treatment or, even better, the separation of surface water from the sewerage network.”

In total, nearly 100 improvement projects relating to the discharge of untreated water are being completed in the Wessex Water region by 2025, part of a £3-million-a-month investment to reduce the number of hours storm overflows operate for by around 25 per cent. A further record-breaking £400 million towards the goal of reducing the activation of overflows will be invested between 2025 and 2030, subject to approval by industry regulators.

Thanks to Wessex Water for sponsoring this Awesome Project and helping to Make Water Famous. If you have a project you would like to see featured, do get in touch.