Warleigh Weir

Warleigh Weir, a location along the River Avon near Bath, is visited by people who use the stretch of river for recreation, including swimming.

Latest data | Monitoring storm overflows | The facts

We have been working with the landowner, the Rivers Trust, Bristol Avon Rivers Trust and the Environment Agency to discuss river water quality at the location, which can be affected by a number of factors – from our storm overflows and treated wastewater from our water recycling centres being returned to the river upstream to agricultural run-off, septic tanks, road drains and wild animals. 

In September 2020 intensive water quality monitoring took place, involving a partnership with The Rivers Trust with Bristol Avon Rivers Trust, Wessex Water, Sewage Free Swimmers and the Environment Agency, and a team of volunteers.  

To understand more about water quality at this location, investigative work is underway to find out more about the factors in the large river catchment upstream of the site which influence the condition of the river water and the role our assets have. This work involves collecting water quality information and river flow and weather data from Warleigh Weir and the catchment upstream, as well as trialling real-time water quality monitoring sensors in the river.

View latest water quality data

Warleigh Weir from the riverbank

Real-time bacteria monitoring trial

The quality of bathing waters is measured by looking at the concentration of faecal indicator bacteria present in them. There is currently no technology that can continuously measure the concentration of these bacteria in rivers, which means we can’t provide people with this information in real time. Instead, samples have to be collected by hand and taken to a laboratory where the bacteria are analysed under controlled conditions, which takes around three days.

However, there are many readily available sensors that can provide robust real-time measurements of other water quality indicators, including temperature, pH, conductivity, dissolved oxygen and river flow. We are working with UnifAI, a company specialising in the use of artificial intelligence (AI) technology, to trial an approach that uses algorithms to develop relationships between these readily measurable parameters and the concentration of bacteria in water.

The trial, which will take place between 2021 and 2023, will involve installing a series of sensors, collecting water samples and analysing bacteria in the laboratory. As more data is collected, the AI will develop these relationships, which will hopefully allow us to stop analysing samples in the laboratory and start providing the public with real-time water quality notifications.

Monitoring storm overflows 

Storm overflows act as relief valves, allowing excess stormwater to be released to rivers or the sea. This protects properties from flooding and prevents sewage backing up into streets and homes during heavy storm events.

We monitor when storm overflows are in use that affect bathing waters and information is provided on Coast and rivers watch. This now includes information on when our storm overflows operate which affect some inland waters, including Warleigh Weir. You can find out the location of storm overflows and how often they are in use on our online mapping system.  

We have extended our notification system which now includes when the following sites are in use, which are upstream from Warleigh Weir: 

  • Culver Street, Bradford on Avon
  • Monkton Combe, Mill Lane
  • Freshford Water Recycling Centre (formerly known as sewage treatment works)

This information is sent to the landowner and anyone can use either our Coast and rivers watch system or the Surfers Against Sewage SaferSeas (and Rivers) app to find out when they have operated. The SaferSeas app also allows you to register for live information on these overflows.   

River Avon and wild swimming

The facts

There has been some misinformation around storm overflows and how they were designed to operate along the River Avon to protect properties from flooding and prevent sewage backing up into streets and homes during storm events. So here are the facts:

River water quality

  • The Environment Agency is responsible for directing what is required to ensure river water quality meets environmental standards.
  • River water quality can be affected by a number of factors, from agricultural run-off, septic tanks, road drains and wild animals, to storm overflows and treated wastewater from water recycling centres.
  • The environmental condition of a river is determined by more than 80 parameters prescribed by the Water Framework Directive – these include nutrients, dissolved oxygen, pesticide and other chemical levels.
  • The way public health risk is measured is very different to environmental health.
  • Public health parameters utilises faecal microbiological parameters, such as the bacteria E.Coli, as an indicator of risk, but there are a number of other factors that could also affect the health of river users, such as pesticides and Weil’s disease.
  • There will always be bacteria in rivers from natural sources, such as wildlife faeces.

Storm overflows

  • Storm overflows operate when the sewer system is full and before sewage surcharges into properties. The majority overtop and weir and have filters in them to prevent any debris escaping.
  • The discharge is incredibly diluted by the rainwater or groundwater that is filling up the system. What discharges has a very low organic load which is why pollution incidents do not generally occur when they operate.
  • Storm overflows are regulated by the Environment Agency. We monitor when overflows discharge and provide the information on our website. We also provide near real-time information about overflows that many affect bathing waters and this information is provided on our Coast and rivers watch website page.

Wild swimming

  • Storm overflows have little impact the environment, but the levels of bacteria released would not meet bathing water standards. In fact, with or without storm overflows in use, river water quality wouldn’t meet bathing water standards. This is due to many other sources such as discharges from sewage treatment works, agriculture and wildlife itself.
  • Wild swimming is never entirely safe, so a sensible risk-based approach should be taken.
  • Not ingesting river water and covering any open wounds will help prevent against infections from rivers, which can have high viral and bacterial loads.

Investment and costs

  • Each and every year we invest more money than we receive through customer bills – see graph below. This investment, approved by Ofwat, comes at risk. The profits made by companies are set by the economic regulator. Under the incentive-based mechanism, companies that outperform the set levels of service to customers and the environment received additional rewards and those that underperform incur penalties. The shareholder carries this risk and reward.
  • It is estimated it would cost around £10 billion to eliminate overflows in our region. To help fund this, customers would see around a 50% increase in bills over 10 years.
  • The outcome of eliminating storm overflows would see little improvement in river water quality or public health benefit for wild swimming as other influencing factors remain. Meanwhile, there would be increase carbon emission consequences, due to the need to construct large tanks and install energy-intensive UV processes.

Investment and customer bills comparison

Our society

  • Most homes contribute to overwhelming sewers during times of heavy rainfall. This is because in many areas, rainwater runs off roofs and paved areas into our sewers, which overwhelms the pipes capacity.
  • Separating surface water from foul water is key and would eliminate the need for storm overflows. We’re calling on government to take a different approach and encourage the decentralisation of surface water management by enabling ‘uncombining’ at the point at which rainwater gets mixed with foul water.
  • With more and more impermeable area being connected as people pave over gardens and increase driveways for electrical charging points for cars, combined with climate change which leading to more  intense storms, the problem will get worse.

What can people do to help?

Installing water butts to collect rainfall and soakaways to allow rainwater to naturally drain away would mean there would be less surface water in the sewerage network and reduce the need for storm overflows to operate. Customers who do this also received a reduction in the bill through our surface water drainage allowance. 

Find out more about storm overflows

Wild swimming

Wild swimming is an activity that takes place in some natural waters, such as rivers and lakes.

Coast and rivers watch

Coast and rivers watch is our online overflow notification system which provides near real-time information of when storm overflows have operated at designated bathing waters and at other water bodies used regularly for recreation.