Designed to prevent sewage flooding in homes, storm overflows operate automatically during or after intense rainfall and release predominantly rainwater into rivers and the sea. They are permitted by the Environment Agency.
Discharges during the bathing season near designated bathing water locations have more than halved, with 87 occurring between 15 May and 30 September 2021 and 39 during the same period this year.
The water company said exceptionally dry weather was a factor in the latest figures, with less rainwater in the combined sewer network, while it is spending £3 million per month on schemes to help reduce the frequency of discharges – starting with those that operate most frequently or have any environmental impact.
Wessex Water has also published the number of overflow operations at designated bathing waters and popular outdoor swimming sites over a 12-month cycle (October 2021 to September 2022), data which is available all year round and provided to Surfers Against Sewage for the Safer Seas and Rivers Service app.
While river sites such as Warleigh Weir near Bath are not yet designated bathing waters, the majority of beaches in the Wessex Water region are and have good or excellent water quality according to Environment Agency sampling. Results for 2022 will be published by the Agency later this month.
Wessex Water is leading an initiative at Warleigh where sensor data is augmented by artificial intelligence (AI) in order to provide near real-time water quality information, based on bacteria levels, to swimmers.
Matt Wheeldon, Director of Asset Strategy, said: "These figures demonstrate the importance of rainwater separation at source – removing rainwater that enters combined sewers from roofs and roads is tackling the root cause of storm overflow discharges.
"Climate change means more intense rainstorms are happening, including during summer months, so we’re investing in rainwater separation schemes as well as sewage storage and treatment solutions."
Wessex Water said removing storm overflows completely would involve digging up almost every local road, costing in excess of £10 billion and leaving an enormous carbon footprint, which was why separating rainwater at source so it doesn’t enter sewers was the best solution.
It was the first UK water and sewerage company to provide overflow discharge alerts 365 days a year, with complete coverage around the coasts. False alarms can sometimes be caused by factors such as wildlife triggering a sensor or mobile network failures – these have been excluded from the 2022 analysis, although the data table includes the total number of email alerts.
Wessex Water's Storm Overflows Improvement Plan outlines how £150 million will be invested between 2022 and 2025 to address intermittent discharges. Our latest Coast and Rivers Watch annual report.