A new 835m sewer underneath the town of Ilkley in Yorkshire will reduce the frequency and duration of discharges to the River Wharfe - home to the UK's first official inland bathing waters.

The sewer is 2m in diameter and can store up to 3.4 million litres of wastewater. It took 16 months to complete, according to the region's utility, Yorkshire Water.

As an interceptor sewer, it receives flow from a number of other large sewers or outlets and conducts it to another outlet, in this case Ilkley wastewater treatment works. The pipeline runs from Wharfe View car park to Ashlands playing field and then crosses under a major road - the A65 to reach the works.

The £15m interceptor sewer and detention tank will hold wastewater during heavy or prolonged rainfall events, allowing it to be stored and then pumped to Ilkley wastewater treatment works to go through the full treatment process once the rainfall event has passed. It is expected to reduce the frequency of discharges from Rivadale storm overflow by 40%, and reduce the volume of wastewater discharged during those events by 50 percent.

This is expected to improve water quality in the River Wharfe, which is home to the UK’s first inland bathing water in Ilkley.

Remote-controlled tunnelling equipment was used throughout the project to reduce disruption. This allowed the sewer to be constructed without closing the A-road.

Nicola Shaw, chief executive of Yorkshire Water, said, “Since the River Wharfe in Ilkley was granted bathing water status, we have been keen to play our part in improving water quality. This includes working on a variety of projects to make improvements to water quality in the river and reduce the impact of our operations.

"This new interceptor sewer is the largest of these projects and it will make a difference to the number of discharges into the river.

“The completion of this project is not the end of our work in Ilkley. Later this year, we will start further work to reduce discharges into the river and are currently assessing a range of possible options, using nature-based solutions where possible.”

The UK government's water minister Robbie Moore said, “As the first designated inland bathing water, the health of the River Wharfe is vitally important both environmentally and socially – and I am pleased to see Yorkshire Water invest in the long-term wellbeing of these waters.

“This government set strict new targets on water companies to reduce sewage discharges from storm overflows, driving the largest infrastructure programme in water company history of £60 billion over 25 years, and prioritised action at bathing waters, such as on the River Wharfe.”

Yorkshire Water’s interceptor sewer project was extended in July 2023, with an additional 191m sewer constructed between Wharfe View Car and the riverbank off Castle Road. This section of tunnel has been completed and will be commissioned in 2026 to ensure Yorkshire Water’s Rivadale storm overflow meets new government targets of one spill per bathing water season, nine years ahead of the 2035 deadline.

Shaw added, “The extension of the interceptor sewer project enabled us to complete tunnelling work while equipment was present on site, improving efficiency and reducing costs, which ultimately provides value for money for our customers. Further upgrades to the network is required before the extension can be commissioned, but it is due to begin operation in 2026.

"It will reduce discharges from Rivadale overflow to one per bathing water season and less than 10 per year, ahead of the 2035 deadline.”