A new reservoir – the South East Strategic Reservoir Option (SESRO)

What is the project?

This is a reservoir in the Upper Thames catchment, south west of Abingdon in Oxfordshire. The reservoir will be filled with water from the River Thames in winter, when there is plenty of water in the river, and when river levels drop, or demand for water increases, water would be released from the reservoir back into the river for re-abstraction downstream. As well as providing a resilient water supply for the South East, the reservoir also provides opportunities to create new habitats and increase biodiversity, as well as provide new leisure and recreation facilities.

Why do we need a reservoir?

We’ve considered a range of options in the development of the plan. The detailed modelling and sensitivity assessments completed by WRSE have confirmed that the reservoir is an integral part of the best value plan for the South East.

In our draft plan we explained that the decision around the size of the reservoir was finely balanced between 100 Mm³ and 150 Mm³. We’ve taken into account feedback from regulators, stakeholders and our customers and completed further modelling work in collaboration with WRSE which have concluded that the larger, 150 Mm³, reservoir is needed.

It’s hard to predict what all our challenges might be over the reservoir’s expected life span (up to 250 years), but a larger reservoir provides a resilient source of water with low operating costs. It can ensure sharing of water and so provides the ideal base of an adaptive plan for an uncertain future.

A 150Mm3 reservoir would also give us around 50% more water for around the same level of investment compared to a 100Mm³ reservoir. The reservoir would provide water to customers in London and the Thames Valley as well as customers served by Affinity Water and Southern Water.

Have we listened to local concerns and how has it shaped the plan?

We’ve listened to the concerns in the community and in February 2023 we published a statement of community commitments to reassure the community that we’re listening. One of the commitments is that we’ll continue to engage and consult with local communities as part of the ongoing planning process.

That’s why we asked for your feedback on the size of the reservoir as part of the consultation

We will:

work with the community to develop a design that delivers opportunities for accessible recreation, leisure and education.
Be open to ideas for community partnerships, including the creation of new open spaces, orchards and woodlands.
Work with schools and colleges to develop opportunities for local training and employment.
Work with local groups to incorporate activities such as sailing, fishing, bird watching, paddle/wind sports, running, cycling and trail walking – as with other lakes across the UK.
Create new wetland habitats, that will help increase biodiversity and capture carbon.
Provide opportunities for local access for the residents of the nearest villages, with visitors from further away being routed to a dedicated visitors centre.
Design embankments that are grassed, with gradual slopes, landscaped and set back from the nearest villages.
Comply with the Reservoirs Act 1975, which sets strict safety standards and requires the appointment of an independent engineer to ensure they are followed.
Design drainage systems to collect surface water and manage it, helping to reduce future flood risk.
Develop plans that locate site entrances away from the local villages and maximise the use of the railway to minimise movements by road.
Carry out an Environmental Impact Assessment and develop a Code of Construction Practice that shows how we have addressed the concerns of local communities.
Deliver best value for customers – learning from the success of Thames Tideway Tunnel, which is being constructed by a new, competitively tendered Infrastructure Provider, from which our shareholders do not profit.
Engage in a continuous dialogue with local communities through a dedicated engagement manager and more formal consultation as part of the rigorous planning process.

What happens next?

We’ll continue to do more detailed engineering, project design and environmental studies to develop the project prior to a formal planning application. We’ll continue to engage and consult with local communities and stakeholders throughout this work.

Why is the reservoir chosen instead of the Severn Thames Transfer?

We need to develop a new strategic resource option in the western part of the South East region to ensure we have sufficient water in the future. We considered both the reservoir and a transfer from the River Severn to the River Thames as potential options to meet that demand. The technical assessments showed that a reservoir is a better choice because it’s more cost effective, has a lower carbon budget and it provides more environmental and resilience benefits, particularly under severe future scenarios.

What happens now to the Severn Thames Transfer?

There are significant uncertainties in planning water supply for the next 50 years. We know we can’t take risks with our water supply and therefore we’ve proposed that we should continue to develop the transfer scheme as a reserve option, which will allow us to act quickly if additional water is needed in the future.