By Alexandra Bassingham
The Chipping Sodbury tunnel, to the north of Bristol, was built in 1901 and is prone to flooding during wet weather.
A lagoon was installed in 2018 as part of a flood alleviation scheme designed to improve the resilience of the railway line.
Network Rail is working alongside the Environment Agency, South Gloucestershire Council, the Farming and Wildlife Advisory Group and Wessex Water to find long-term solutions to flooding.
The project will see 200m (656ft) of track raised by 20cm (7.8in) at the western end of the tunnel with overhead cables adjusted accordingly.
Drainage channels will also be dredged throughout the tunnel to allow more water to be collected.
Two water removal pumps are being replaced at the western end of the tunnel, and surveys and design work carried out for future replacement of two pumps at the eastern end of the tunnel.
GWR station manager for Bristol Parkway Marcus Deegan said the work is the latest in a wider scheme to “ease the effect of flooding on the railway and in the surrounding area”.
During the work, there will be fewer services between south Wales and London, with that route also affected by longer journey times on Sunday 20 July due to follow up work.
Between the 7 – 13 July, additional peak-time trains will run between London Paddington and Swindon.
During the works, passengers should check journeys in advance, Mr Barratt said.