SESRO – the clue is in the name
With public consultation on the proposed new reservoir in Abingdon, Oxfordshire, underway, WRSE’s technical director Meyrick Gough explains the need for the new resource and its role in the regional plan for South East England.
Like many reservoir schemes, there is a long history associated with the plans to build a new reservoir in Abingdon, now known as SESRO (South East Strategic Reservoir Option).
With few suitable locations in the South East to build reservoirs – due primarily to geological factors – SESRO, like Havant Thicket and Broad Oak, has been on the option list for many years but its implementation is now more crucial than ever.
For the first time, the long-term needs of environment have been forecast and included within WRSE’s revised draft regional plan and the water company Water Resources Management Plans (WRMPs).
This could require up to 1.3 billion litres of water to be left in the environment by 2050 to help protect sensitive sources including world-renowned chalk streams.
The regional plan also increases the resilience of our water supplies to a 1 in 500-year drought and reduces our reliance on environmental drought orders and drought permits in the management of drought events.
SESRO is a key piece of the puzzle in delivering these new policy requirements right across the WRSE region.
The case for need
The advent of regional planning has given us the opportunity to take a fresh look at the future challenges we face and what this means for our water supplies. We’ve considered all the options that could provide more water, looking beyond the boundaries of individual water company areas, to identify the optimum mix of solutions that address the future shortfall in water supplies across the region.
To achieve this, we have completed extensive regional modelling, that has planned for a range of future scenarios and looked at many different configurations of options. This work has consistently shown that SESRO is a central part of the regional solution and is not only needed to meet the collective challenge of population growth and climate change but also to replace water supplies that are currently taken from the more sensitive water sources across the region.
We’ve used several data sources that have provided a wide but plausible range of scenarios for us to plan against, enabling us to show which schemes are needed in different futures. Our modelling shows that even in the lowest population growth and climate change scenarios, combined with the most conservative projections for how much water will be left in the environment, SESRO is an important part of the best value solution, but the reservoir by itself is not enough to meet all the significant future challenges in the region.
We looked at a range of sizes for the reservoir across the different scenarios. A key factor to determining the optimum size for the reservoir was how much water could be saved through leakage and consumption reduction, as this changed how much water we would be needed from new supplies.
Between our draft and revised draft plan, the amount of water to be provided through reductions in demand increased, driven by the interim targets included in the Government’s Environmental Improvement Plan (EIP). This in turn means that less water needs to be provided by new sources in the first 15 years of the plan. This changed the mix of solutions and the size of SESRO.
In our draft plan, where the supply deficit was greater, the combination of a 100m3 reservoir alongside the Severn to Thames Transfer (STT) was the preferred solution to address the projected shortfall. In our revised draft plan, with a smaller deficit to be filled in the early years, a larger, 150m3 reservoir was identified in most scenarios. This option provides a greater level of resilience and the ability to adapt for the future. It also enables companies to progress with reducing abstractions from sensitive water courses.
In the more adverse future scenarios, additional schemes would be delivered alongside SESRO to address the greater shortfall in supplies. It is for this reason that the STT scheme will continue to be progressed as a potential alternative option for the future, in addition to SESRO.
When SESRO is removed from the option list, the schemes that replace it would cost around £1.3 billion more on average - and £3.4 billion more for scenarios where greater levels of abstraction reduction are required and less water is available due to climate change.
Furthermore, building SESRO by 2040 will also help us to adapt if the highly ambitious reductions in customer water consumption are not achieved. It provides time for alternative options to be progressed should the water savings from new government policies and customer behaviour change initiatives, not be realised.
SESRO’s role in the regional plan
SESRO will store water from the upper River Thames during the winter, holding 150,000,000 m3 that would have previously continued to flow downstream and out to sea. Having the ability to capture this water provides us with up to 270 million litres per day to supply customers for many years to come, while also helping us to adapt to a changing climate with wetter winters and drier summers.
The water it holds will be moved East and South and consumed by customers of Thames Water, Affinity Water and Southern Water. It will provide a critical new resource for London and the Thames Valley, delivering much needed resilience to the water supplies of both residents and businesses that are so important to the UK economy. The transfer of water to Hampshire and Affinity Water’s north London zones will mean that more water will be left in some of the region’s most sensitive chalk streams, including the rivers Test, Itchen and Kennett as well as enabling abstraction to be reduced from other sources too.
There are indirect benefits over the longer-term to even more customers that the regional modelling has identified. The transfer from Thames to Southern will move up to 120 million litres per day, and once in place will mean that some of the area’s existing water supplies can be shared with its other neighbouring companies – South East Water and Portsmouth Water. This increased connectivity over time has been unlocked by regional planning and is essential part of securing our water supplies for the future.
So, the clue is in the name. SESRO is the definition of a truly strategic regional option, directly supplying 15 million people and indirectly benefiting many more across the South East.
If you are interested in finding out more, Thames Water’s public consultation is open until 28 August 2024.
