A reservoir embankment trial, which will help to inform Thames Water’s plans for a new reservoir near Abingdon, has received planning permission from Vale of White Horse District Council.

The backing from the council’s planning committee means Thames Water can develop its understanding of the ground conditions at the site, south west of Abingdon, where it proposes to build a new 150 billion litre reservoir. 

The utility company said this was a major step in developing the design proposals for the reservoir, known as SESRO (South East Strategic Reservoir Option). 

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It’s anticipated that contractors working on behalf of Thames Water will begin embankment trials this summer to understand how the local clay reacts when compacted.

Derek Stork, a spokesman for GARD (Group Against Reservoir Development), said the latest development did not mean the reservoir 'has any sort of go-ahead' and campaigners are still calling for a public inquiry.

During the trial, the company will excavate the clay and layer it into three mounds, each 50 metres long, 20 metres wide, and up to two metres high.

Ground investigations are already under way.

Leonie Dubois, Thames Water’s Head of Engagement, Land and Consents said: “We listen carefully to residents and understand that they want assurances about the design and integrity of the reservoir.

Oxford Mail: "This is why we’re starting the process to understand local ground conditions at a really early stage.

“As the population grows and the effects of climate change continue to take hold, demand for water will only increase. We’re serious about tackling water leakage and reducing consumption levels, but that alone isn’t enough. We must build more resilient infrastructure to avoid a future crisis and the reservoir has a vital role to play.”

The results from the trial, which will take place over a 12-month period, will play a crucial role in informing the engineering design and embankment construction proposed for this vital new water supply.

The scale and significance of SESRO, as a means of tackling future water shortages for the southeast, has led to its classification as a nationally significant infrastructure project (NSIP).

The reservoir would help to secure future water supply for local Oxfordshire residents, as well as 16 million people across the Thames Water, Southern Water and Affinity Water catchments.

The strategic case for the reservoir is outlined in Thames Water’s revised draft Water Resources Management Plan, which is currently with the government for consideration.

Oxford Mail: A map showing the reservoir landThe plan sets out a range of investment measures proposed to combat the effects of climate change and population growth in London and the wider southeast region.

Lee Dance, Organisational Director at Water Resources South East, said: “SESRO is a important part of the forward-looking programme of investment in our water supplies, set out in our regional plan, which will provide water to people across the South East."

Proposals for the new reservoir are being driven by Thames Water’s Strategic Resource Options (SRO) team, a dedicated project team tasked with delivering solutions to tackle the future drought scenarios which threaten London and the southeast.

Thames Water’s SRO team is currently preparing for a programme of public consultation, and throughout the summer months, local communities will be asked to share their views on the latest proposals for the reservoir, with feedback shaping the plans.

Should Thames Water secure government approval for SESRO, it intends to submit a Development Consent Order (DCO) in 2026, seeking permission to construct and maintain the new reservoir.

If granted, construction is forecast to begin in 2029 with SESRO planned to begin operating in 2040. 

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About the author 

Andy is the Trade and Tourism reporter for the Oxford Mail and you can sign up to his newsletters for free here. 

He joined the team more than 20 years ago and he covers community news across Oxfordshire.

His Trade and Tourism newsletter is released every Saturday morning. 

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