Stroud Sewerage

About This Project

The £22 million Stroud Sewerage Strategy Project (Part 2), led by Severn Trent and Galliford Try, aims to reduce sewer flooding and improve the health of the River Frome by upgrading Stroud’s sewer infrastructure. The project includes 3.65km of gravity-fed trunk sewer—built using a mix of open cut and pipe-jack tunnelling with four TBMs (Molly, Lilian, Suzanne, and Florence)—to redirect flows from Wallbridge CSO to a new CSO site. Twelve shafts (3.66m–6m diameter) were designed by BSP Consulting, with a bespoke TBM setup by Active Tunnelling for a critical 900mm micro-tunnel. Additional works include the installation of a prefabricated interception chamber connecting four major pipelines, open-cut River Frome crossings with ecological safeguards (over 1,550 fish relocated), and the construction of a 25m diameter, 28m deep CSO shaft. Surface water from 3.88ha in Stroud town centre was diverted via a new 555m sewer network and 232m auger-bored connection to the Stroudwater Canal, significantly reducing spills. Infiltration was reduced by sealing 475m of old sewers and manholes. As of July 2023, final works include upgrades to storm return systems at Stanley Downton WwTW and demolition of the existing CSO. The project overcame major technical, environmental, and stakeholder challenges through close collaboration across a wide specialist supply chain.