Our revised draft regional plan

The selection of the preferred regional plan (our revised draft plan) involves, among other factors, a comparison between the total capital and operating costs of all of the schemes in the plan, which are required to solve the future water deficits.

Given that the outputs of the two schemes are also different, with the reservoir providing a greater amount of water, versions of the regional plan that feature the Severn to Thames Transfer (STT) need to include additional schemes to provide the additional water needed in the years ahead. Therefore, a like-for-like cost comparison can be misleading, as the two projects, and the associated versions of the regional plan they sit in, are very different. However, the capital and operating costs of these two schemes, and many other schemes, are detailed in Thames Water’s revised draft Water Resources Management Plan (WRMP) tables, which will be published shortly, following regulatory quality assurance and redaction for commercial reasons. Detailed cost estimates are also provided in the RAPID Strategic Resource Option (SRO) Gate 2 documentation for each scheme.

When constructing the different versions of the regional plan, the investment computer model we use is free to select neither scheme, or one scheme, or both schemes together. The decision on the selection of schemes in our revised draft regional plan is based on the overall cost of the plan, as well as best value metrics, government policies, plus regulatory guidance and targets.    

When comparing the two schemes, both involve significant initial capital investments in order to develop and build the key infrastructure involved. The reservoir scheme has the construction and interconnectivity (transfer pipeline) costs. Likewise, the Severn to Thames Transfer scheme also includes construction costs for the Vyrnwy bypass and interconnector between the two rivers or between the canal and the River Thames.

Furthermore, the reservoir has a different, smaller, operating cost, compared to the operating cost of STT. The STT has significant ongoing operational costs, in the form of fixed operational expenditure payments to United Utilities (UU) / Severn Trent Water - in order to fund replacement water sources for UU’s current customer base and/or development of infrastructure, as applicable. There’s also variable operational expenditure costs, due to pumping and treatment requirements. As such, the overall cost of the STT depends on the phasing of the scheme and the total volume of water required.

In the options appraisal process for their water resource management plans, water companies can consider re-using gravel pits as a potential source of new water. This can, however, come with engineering, environmental and planning challenges. 

Water levels in existing gravel pits are largely related to the water table, so can fluctuate, particularly with seasonal variations in groundwater levels.  So as to retain water in the gravel pits during a drought, when the surrounding groundwater level falls, it would be necessary to seal the gravel pits, most likely using clay and there are significant environmental concerns around conducting engineering works to seal gravel pits after they have been restored and wetland habitats have become established. 

An option is included in the feasible list for development of storage at locations where gravel extraction is either underway, or planned, and so where installation of a clay cut-off to seal the site could be undertaken prior to site environmental restoration/landscaping.  This option is specifically included to provide resource in the event that a water supply is required for the restored Cotswold Canals. 

There is also a strategic scheme being developed by Wessex Water and South West Water under the RAPID Gated process to repurpose deep quarries in the Mendips, under the West Country Water Resources regional plan.  Please visit the Ofwat website for more information on this “Mendip Quarries” scheme, which gained approval to progress to Gate two, which is due to be submitted in July 2023.

There are a few aspects here:

1. Greywater and rainwater reuse for new developments: These are being considered as they have a demonstrable track record of being safely installed and maintained, and can be cost effective. This will require government to change building regulations to enable the scale of activity required, and to control the risks of cross connection and public health impacts once it has been installed. We have included this in the government-led initiatives in our plan and support government taking action to increase the efficiency of new and existing homes. 
2. Retrofitting greywater and rainwater reuse: Although this is technically feasible, it carries an unacceptably high risk to public health due to poor installation or subsequent poor plumbing practices when it needs maintaining. There is also a question about how water companies can work with their household customers to install, maintain or upgrade these systems over their lifetimes. Retrofitting is also prohibitively expensive, except in very specific communal hosing arrangements, and would cause unacceptable increases to customers’ bills.
3. Our draft regional plan includes several water recycling schemes, which undertakes a similar activity at a larger scale. 

Water companies already liaise with local planning authorities and developers concerning new developments, and will continue to strongly advocate and promote higher standards for water efficiency in new builds.

More broadly, we support government interventions, such as labelling water using products and tighter building standards, that would make new homes more efficient and help improve the water efficiency of existing homes.

In developing our draft regional plan, WRSE have considered a large number of potential solutions including new reservoirs across the South East. 

A range of sizes have been considered for the reservoir in Oxfordshire from 75 million cubic metres (Mm³⁾ to 150 Mm³, as well as two dual phase options (30+100 Mm³ and 80+42 Mm³). 

The draft regional plan has identified that the 100 Mm³ reservoir in Oxfordshire offers best value. However, the other sizes remain feasible and will continue to be considered in the refinement of the draft plan and examined through the studies being undertaken through the RAPID Gated process. Further information on the work completed to date to examine the proposed reservoir in Oxfordshire (referred to as SESRO) can be found here https://www.ofwat.gov.uk/regulated-companies/rapid/the-rapid-gated-process/gate-two/. 

The reservoir in Oxfordshire would serve customers in the Affinity Water, Southern Water and Thames Water areas and these water companies are currently consulting on their draft Water Resources Management Plans (dWRMP24s) until 20 February (for Affinity Water and Southern Water) and to 21 March 2023 (Thames Water). Please visit the water companies' websites to read their draft plans and provide feedback. The water companies will consider all the representations received to the statutory consultations and explain any changes to their draft plans as a result.

In response to your concerns that a reservoir of this size is untested and poses a tangible threat to local communities, we would like to reassure you that this is not true. In an international context, SESRO constitutes a large reservoir, however, there are many which are larger. In addition, the use of earth embankments on a similar scale to impound reservoirs is very well established. There is a World Register of Dams maintained by the International Commission on Large Dams, which highlights that there are many dams around the world of comparable or greater scale to SESRO. On the 2020 register there are, internationally,:

- 7,200 earth embankment dams with earth cores and with a dam height of at least 15m

- 1,971 earth embankment dams impounding a reservoir volume of at least 150Mm³

- 121 earth embankment dams with a crest length of at least 10km.

In the UK, there is a long history of embankment dam construction, and there are numerous significant dams still in operation which were constructed around 200 years ago.  

The proposed SESRO embankment will have a height of around 15-25 metres above ground level, and there are many embankment dams with a clay core in the UK which are significantly taller than this, including Llyn Celyn (58m), Megget (56m) and Kielder (55m) (Source: British Research Establishment (BRE) register of UK Dams). Furthermore, Thames Water currently operates several reservoirs which are comparable to SESRO, namely, King George VI, Queen Elizabeth II, Queen Mary, Queen Mother and Wraysbury all have dam heights of between 12-20 metres.

In terms of safety, the UK water industry has an excellent record of reservoir safety. The design would meet the requirements of the Reservoirs Act 1975, be reviewed by an independent Reservoir Advisory Panel, and adopt appropriate security measures.

Please do not hesitate to get in touch if you have further queries or concerns. 

The WRSE regional plan considers the supply-demand balance across the 37 water resource zones in the South East. 

We have used an adaptive planning approach to mitigate risks around uncertainty in supply and potential changes in demand, which considers a range of different future scenarios, and incorporates potential changes to available river flows and groundwater sources. 

Please go to Thames Water’s draft Water Resources Management Plan (dWRMP) consultation website www.thames-wrmp.co.uk to read more detailed information on the Guildford Water Resource Zone (WRZ) - specifically, visit Section 6 to understand the supply demand position in Guildford WRZ and Section 11 to read about the proposed actions in Guildford WRZ.

WRSE has considered a range of sizes for the proposed SESRO reservoir, which have been incorporated into our investment modelling and best value planning process to determine the programme of schemes in our draft regional plan. 

Whilst the draft regional plan has identified that the 100Mm³ reservoir may offer best value at this stage, the other capacities (75, 125 and 150Mm³) remain feasible, and will continue to be developed further and progressed through the RAPID Gated process. 

In addition to SESRO, the draft regional plan is proposing the development of other new sources of water and sets out the reasons for the choice and sequence of these schemes, including the development of a new reservoir in Oxfordshire, followed by a transfer from the River Severn. 

Please also visit Thames Water’s draft Water Resources Management Plan (dWRMP) consultation website www.thames-wrmp.co.uk and read Sections 10 and 11 of Thames Water’s draft plan document to understand the decision making process to inform the draft plan (Section 10) and the overall draft plan (Section 11).

Southern Water is proposing a new reservoir near Blackstone in West Sussex. This is referred to as the River Adur Offline Reservoir in the company's draft WRMP24 technical documents. 

This reservoir would have a capacity of 4.6 billion litres of water and would supply around 20 million litres per day to customers across Sussex. This new source is needed by 2045.

The reservoir would be filled by pumping a maximum of 30 million litres of water per day from the eastern branch of the River Adur. It would then be treated at a nearby supply works, before being distributed to customers. 

Reservoirs are complex projects and their planning can take a long time. Southern Water expects this project will take over ten years to plan and build. 

After 2025, Southern Water will start more detailed planning, including engaging with local communities, as it identifies a suitable location - providing more detail on the exact location, size and shape of the reservoir and, where needed, beginning any necessary planning consultations before construction begins.

The current chair of the Environmental Advisory Group is our Organisational Director, Trevor Bishop. The Environmental Advisory Group is made up of a mixture of Environmental NGOs, regulators and water company environmental leads. The remit of the group is to review the WRSE methods relating to the environmental assessments, and the outcomes from this work which have fed into the draft regional plan. 

With regards to the return of water to the environment, the water companies in the South East are working with regulators to ensure that abstraction from rivers and groundwater is sustainable, leaving more water for the environment in future. 

The draft regional plan considers the statutory obligations (for example, abstraction licence capping and Water Industry National Environment Programme (WINEP) investigations) as well as proposed future reductions in abstractions, referred to as environmental ambition. This ambition has been incorporated into the draft regional plan in specific scenarios through our adaptive planning process. 

WRSE will continue to work with our member water companies and environmental regulators and NGOs to understand the scale, location and prioritisation of abstraction reductions, as well as the costs and benefits of environmental ambition. More information can be found in our draft regional plan consultation document, on pages 8, 14 and 15.

Further details are set out on page 29 of our draft regional plan consultation document. 

A total of four new reservoirs are included in our draft plan, namely:

- Broad Oak Reservoir near Canterbury in Kent (completion by 2036)

- South East Strategic Reservoir Option (SESRO) near Abingdon in south Oxfordshire (completion by 2040)

- Blackstone Reservoir near Henfield in West Sussex (completion by 2046)

- Broyle Place Reservoir near Lewes, East Sussex (completion by 2075).

In addition, our plan includes the Havant Thicket Reservoir, which has already received planning permission and is under construction. This will be completed by 2029. An existing Canal & Rivers Trust Reservoir at Brent in north London could be repurposed for public water supply by 2046, plus the capacity of the existing Bough Beech Reservoir near Edenbridge in Kent could be increased by 2051.

Further details are set out on page 29 of our draft regional plan consultation document. 

However, in summary, a new reservoir is planned to be in place by 2046 at Blackstone, near Henfield in West Sussex, to serve the surrounding area. 

Increasing the capacity of the existing Bough Beech Reservoir at Edenbridge near the Surrey / Kent border is included in our draft plan for completion by 2051. This would provide additional water for SES Water to supply to customers in its area, including Surrey. It could also enable additional water to be shared with neighbouring companies Southern Water and South East Water. 

Finally, a new reservoir at Broyle Place near Lewes, East Sussex, could be needed by 2075 to serve the local area.