Storm overflows, also known as Combined Sewer Overflows (CSOs), are built into the sewerage network and may operate automatically during heavy rainfall to protect properties, businesses and streets from flooding.
Heavy or prolonged rainfall puts pressure on the combined sewer as there isn’t always enough capacity in the network to contain such volumes. Storm overflows are designed to act as a safety valve by discharging automatically into the sea or a river when this happens.
The process is strictly regulated by the Department for Environment, Food and Rural Affairs (Defra) and the Environment Agency.
We’ve produced a handy animation to show how and when storm overflows operate, see our storm overflows page.
As well as sewage in the sewerage system, surface runoff and rainwater can also enter our sewerage network, increasing the volume of flows needing to be transported and treated during periods of heavy rainfall.
At times of increased rainfall or during snow melt, there isn’t always enough capacity to contain such volumes.If we didn’t have storm overflows then the diluted storm water wouldn’t have anywhere to go, which would result in homes, businesses and streets being flooded.
Rest assured we have been working hard to reduce the operation of storm overflows, cutting their use by 50% in 2022, with their duration down by 75%, across our 860 miles of coastline. However, we recognise there is more to do, and we have plans to do it.
We’ve made a commitment to reduce spills from storm overflows to an average of 20 per year by 2025 across the region.
We’re also investing at every one of our designated bathing waters to reduce spills to even lower levels. This accelerated investment enables us to go further and faster in delivering for customers, communities, and the environment.
Our WaterFit programme sets out our commitments and plans to deliver more for our beautiful southwest region.
We’re constantly improving and investing in our network to increase its holding capacity, including installing more storm storage and bigger sewers. We’re also working with other agencies to separate out surface water from our sewerage systems to reduce the pressure on them.
The cost, both financially and environmentally, to remove all storm overflows would be substantial. It would cost billions and cause major disruption digging up urban and rural areas.
Whilst we are investing in our network it’s important to recognise that we can’t increase the capacity infinitely to hold ever growing volumes. That’s why we have teams to identify surface water misconnections and help reduce blockages, which restrict flow in the network. We also liaise with developers, planners and highways departments to help prevent excess surface water entering our network.
Climate change is placing extra demands on our infrastructure with a greater number of periods of intense, heavy rainfall. This presents challenges in managing the sheer volume of flows in our network and we know this will be ever-increasing.
But there are other challenges – such as a 20% increase in population in the South West over the last 30 years.
Tourism has also doubled visitors to the region in the last 15 years.
We model and forecast the impact of an increasing population and the impacts of climate change on our network. We then invest to improve our network. We are working hard to meet these demands and our WaterFit investment programme is designed to reduce the use of storm overflows.
Storm overflows are designed to only operate during periods of intense rainfall, any sewage or wastewater discharged from them will be very diluted as it is mixed with the large volumes of rainwater flowing through the network.
Storm water storage tanks help capture some of the sewer debris through settlement. There are also screens on most storm overflows to help prevent this from entering the water.A number of factors influence water quality and we understand how easily the cause of an issue may be misinterpreted or misrepresented.
Surface runoff from roads, hard surfaces and fields is the most common factors which cause discolouration of the water at beaches. Algal blooms and seaweed can also make the sea look discoloured, smell or cause foam on the surface.Misconnected pipes can also play a part, particularly in urban areas. A misconnection usually occurs when a home or building is newly constructed or extended and the pipes are plumbed incorrectly into surface water drains without our knowledge. Once these misconnections are identified, we will ensure that the private plumbing is corrected, and will notify Building Control if their more extensive powers are required.
Agricultural runoff is the biggest polluter of rivers and waterways as it often carries along pesticides, fertilisers and animal slurry. Urban runoff from roads can also carry pollutants like oil, diesel and petrol.We’re proud to say though that all of our monitored beaches passed the standards for bathing water quality for the second time in a row in 2022.
The Environment Agency provide data on other sources of potential pollution.Your Beach, Your Say, Our Investment - help us shape plans.
We are inviting local community and stakeholder groups, to work with us to help us consider where to prioritise our investment from 2025.
The knowledge you hold about your bathing water is invaluable. We know the bathing waters in our region really well, but we also know that so much insight lies with our customers and beach communities.As we begin refining our investment programme from 2025-2030, we are inviting local community and stakeholder groups, including Parish and Town Councils, to help us prioritise that investment. If you want to get involved fill in the form below. Please note you’ll need to be part of a group to submit.
Tell us about your beach