Project overview
The Great Shefford Flood Alleviation Scheme was designed to intercept and divert excess water from the Great Shefford Stream to reduce the impact of flooding on the nearby village and road. By integrating native planting and sustainable landscaping, the design will enhance biodiversity at the same time as reducing flood risk.
The village of Great Shefford has been affected on multiple occasions by flooding from the nearby stream, most recently in 2014, when burst banks caused damage to homes and infrastructure. The £5 million flood alleviation scheme was commissioned by the Environment Agency with work beginning in summer 2022, completing by the summer of 2025.
Key project stats
Shortlisted in the British Construction & Infrastructure Awards 2026!
The Great Shefford Flood Alleviation Scheme is shortlisted in the Best Projects – Infrastructure, Environmental Project Award. This category recognises the best projects delivering environmental improvements for local communities and regions by mitigating the impact of extreme weather and climate change – along with other environmental hazards – on people, properties and business. WSP Binnies are thrilled to be nominated alongside all the companies delivering this project for the Environment Agency.
We look forward to the award announcements in October.
Our role
Binnies was engaged under the Environment Agency’s Client Support Framework (CSF) to act as the NEC4 project manager and cost consultant. Owing to the need to have the project manager and cost consultant within a reasonable distance of the site to visit, Advantage RSK provided an approved Environment Agency NEC4-accredited project manager and a cost consultant to be responsible for the contract administration of the NEC4 engineering and construction contract (ECC) option C.
This team managed early warnings and compensation events, reviewed and validated contractor quotations, monitored cost performance and programme progress and ensured that contractual obligations were met efficiently and transparently.
High groundwater levels were the biggest challenge on the project. The proposed design route of the pipeline meant pipe jacking or tunnelling was not suitable, as there was not enough cover along the pipeline to prevent the machines from ‘rising’ above the intended pipe route and the chalky ground could fill quickly with groundwater when excavating deeper than the water table.
Extended periods of wet weather meant the water table was higher than usual, and this, combined with run-off water, meant there was a risk that water could inundate the excavations.
The Great Shefford Stream is a tributary of the River Lambourn. As the River Lambourn holds dual environmental designations as both a Site of Special Scientific Interest (SSSI) and a Special Area of Conservation (SAC), ecological protection was a key consideration.
The scheme also required careful commercial management, particularly in relation to challenges such as fluctuating groundwater levels and design amendments.
Additional dewatering was carried out, and the work started later, as it was vital to wait until the groundwater levels were on a sustained downward trend.
Silt pollution can cause serious damage to the environment and lamella separators – a type of sediment treatment tank – were used to remove suspended solids from the water so it could be released back into the river, with groynes deployed to slow the flow of water and encourage sediment to drop out naturally. Silt curtains and booms were placed at the confluence of the river and the new built channel to prevent silt from polluting the nearby waterways.
The 138-metre open river channel was landscaped and planted with native vegetation, to provide new habitat and boost biodiversity, contributing to a +20% biodiversity net gain target while offering a visually appealing outlet.
Advantage RSK acted proactively to manage the project and ensure regular and consistent communications with all parties. Binnies’ established relationship with the Environment Agency through the CSF meant the Advantage RSK team could seek advice and, at times, a second opinion throughout.
The impact
High rainfall and excess water from the Great Shefford Stream will be diverted through the underground pipe and culvert, releasing into the River Lambourn downstream of the village of Great Shefford. This will protect approximately 33 properties, both residential and commercial.
The project has supported the training and development of emerging professionals. Graduate engineers from RSK’s early careers programme have been meaningfully engaged in site visits, contract administration and coordination between the client and contractor. Through this involvement, they have gained practical experience in the implementation of a new engineering contract (NEC) and in the technical aspects of flood risk engineering, helping to build their competence and confidence in real-world project delivery.