Campaigners have renewed their call for a public inquiry after Thames Water was given planning permission for an embankment trial for a new reservoir.

The planning approval from Vale of White Horse District Council means the utility company can now 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. 

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

But 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.

He said: "GARD’s view is that the small scale of the trial embankment, the very limited area over which the soil will be tested, and the short timescale of the test mean that the whole exercise is meaningless as a test of the design and safety of the full-scale Reservoir Embankment.

"GARD has commissioned a review report of the trial and the state of the design of the Reservoir. The report, by a leading UK authority, Professor Chris Binnie, a former member of the Government’s Reservoir Engineers Panel.

Oxford Mail: An artist's impression of the South East Strategic Reservoir"Professor Binnie is very scathing of Thames Water’s so-called trial, and of the reservoir design in general, which he describes as ‘sketchy’.

"Professor Binnie’s view is that the reservoir should not be allowed to go ahead without a large-scale trial embankment (hundreds of metres long) and without an analysis of the consequences of a dam breach, which Thames Water refuse to do before approval is given."

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.

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

Oxford Mail: “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 the reservoir.

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).

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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 catchment areas.

Oxford Mail: An artist's impression of the new reservoirThe 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.

The 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.

If Thames Water does 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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