Costain secure contract to support Thames Water reservoir


Costain has been awarded a Thames Water design contract to support a new reservoir in Oxfordshire.

Credit: Costain Group plc

The 150Mm3 reservoir, known as SESRO (South East Strategic Reservoir Option), is set to supply water to Thames Water, Affinity Water and Southern Water customers in London and Thames Valley.

It also aims to create new habitats, increase biodiversity, and provide new leisure and recreation facilities. 

Costain will conduct clay compaction trials to understand the ground conditions at the proposed site. 

Trails are set to begin this summer and finish within six to twelve months.

Three test embankments are to be built within the proposed reservoir footprint each approximately 50 metre long, 20 metre wide, and up to 3 metre high.

Geologists are then to determine the performance of the Kimmeridge clay under different compaction conditions, with the data gathered to directly impact on the reservoir embankment design and construction methodology.  

Costain has also provided constructability advice as well as design, construction and sequencing recommendations for significant elements of the project.

The company will also provide safety, health, environment and quality (SHEQ) assurance and act as a logistical hub for all ground and environmental investigations.

An Arup and Binnies joint venture has also been selected to be the delivery partner for SESRO, providing all design, consenting and environmental services for the integrated scheme.

Costain was recently awarded a design and build contract, valued at more than £5 million, to upgrade Thames Water treatment sites in Berkshire and Hampshire.

Last year, Thames Water risked collapse following a debt crisis as water companies around the UK suffered similar inflation-related debt crises and national alarm over increased sewage spills.

Graham Sugrue, framework director at Costain, said: “The UK needs to upgrade its water infrastructure to meet increasing demand and remain resilient in the face of climate change. 

“This is a project that will see our customer benefit from the breadth and depth of Costain’s capabilities.”

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