Severn Trent Completes Groundwater Sewer Flooding Prevention Works with Innovative Technology

Severn Trent Water has just completed a £1.4 million scheme in Slimbridge, Gloucestershire to alleviate groundwater flooding issues impacting on the sewer system in the local area.   

A total of 1.4km of pipe was renovated, together with new tank sewers to ensure greater resilience from repetitive incidents of rising groundwater ingress to areas where the pipes had been fractured through weathering.

Groundwater is especially high around the settlements of Slimbridge and Cambridge. This can enter the sewer network through gaps or cracks in pipe sections, joints and manholes. However, these sewers are only designed to carry domestic waste (sinks, toilets, dishwashers, washing machine waste etc.) and a limited amount of rainfall runoff.

When the groundwater table is high, usually during winter months, pumping stations are unable to cope with the quantity of groundwater that enters the network and sewer flooding occurs. Groundwater also provides a base flow for the River Cam and its tributaries.

Groundwater and sewage do not make the best of companions environmentally, hence the need for a comprehensive and effective solution.

Extensive CCTV surveys of foul drainage systems in Slimbridge and Cambridge revealed 49 locations where groundwater was observed to have entered the foul network, so the task was considerable.

Innovative Flood Grouting Technique

Severn Trent considered the area the perfect location to trial an innovative “flood grouting” technique along 600m of the pipe length, where it could be most appropriately used.

Flood grouting is an environmentally friendly, liquid system that uses two different grout materials, which are inserted into the sewers in stages. The grout flows through the damaged sections of pipe, into the surrounding soil particles and then hardens around the sewer pipe when the two grout materials mix together. The technique gives near-perfect water tightness and seals any defects, while also stopping any groundwater from leaking into the network.

Alongside the flood grout trial, more traditional trenchless technologies, including sewer lining, were used to renew the ageing sewer pipes.

This is the first time that Severn Trent has used this grout technique and, following the early findings from the work in Slimbridge, is a method that the company will consider using in the future to address similar ground water infiltration problems.

Severn Trent will continue to monitor the effectiveness of the trial over the coming months, during which time the ground water levels will vary. From a customer and climate change perspective, the flood grouting trial, if expanded across the country, could mean long term fixes, less disruption and more resilience against rising groundwater from wetter winters in the future.

Mapping Resilience against Groundwater Sewer Flooding

GeoSmart are working with a number of water companies to map groundwater sewer flooding risk using their GW5 National Groundwater Flood Risk data overlaid with sewer networks in prone areas.

Our Groundwater Sewer Infiltration Flood Forecasting Service is also helping water company asset managers protect vital community infrastructure up to 30 days ahead of major incidents occurring, through our unique borehole telemetry and modelling.

For more information, contact us on 01743 298100 or email  


Severn Trent Water News Release

Slimbridge Parish Council – FAQs