Parish Council’s response to Thames Water’s Reservoir plans – SESRO

Thames Water held a consulation over the 2025/26 winter.  Visit Thames Water’s website to read more about the plans https://thames-sro.co.uk/

Sutton Courtenay Parish Council’s response was:

Sutton Courtenay Parish Council is a signatory to the joint objection letter by various local parish councils sharing their widespread concerns. In addition there are Sutton Courtenay centric objections to be made as follows.

Ginge Brook
The SESRO exhibition at Milton Hill at the end of November included a plan adding “a water channel” from Ginge Brook to the South of Steventon leading either to the planned
watercourse diversion or water channel around the S.E edge of the reservoir. The writer cannot find this shown on any plans since, and in fact the channel was described at the exhibition as only a proposal. Ginge Brook has flooded leading to house inundations in Sutton Courtenay and this SESRO addition seems essential with floodplain loss.  Confirmation and details required.

Flood Modelling
The 2024 Vale of White Horse consultation response notes the need for inundation modelling for Abingdon, Culham, and Sutton Courtenay including a dam break analysis. Has this been undertaken and results published? For example there is great concern upon the impact of an emergency drawdown of say 76cu.m/second upon Sutton Courtenay. At the height of winter flooding in January 2024 the flow gauge at Sutton Courtenay (close to the proposed pumping station) was measuring 210cu.m/second with water over the road by Sutton
Courtenay Bridge and Culham Lock overtopped. An additional 76cu.m/second would overwhelm Culham Lock and adjacent housing at the northern end of the village and beyond with mass evacuations, (it happens, in 2019 1,500 residents were evacuated at Whalley Bridge, a reservoir near Buxton).

Noise and Pollution
Sutton Courtenay was plagued by pile driving thudding day-long during the recent construction of a data centre at Milton Park. Binding and numerically defined specifications should be provided covering the monitoring of noise, emissions, dust suppression, etc along with operating hours and travel plans.

Addiitonal Engineering Works
The consultation covers the reservoir only. In addition there is to be a pipeline feeding Southern Water, described as being 50 to 85 kilometres long, thus further costs and nearby construction chaos will follow. The SESRO proposal is incomplete without details of this; also any engineering works mserving Affinity Water. Please inform.

The joint letter with neighbouring Parish Councils was:

We, the undersigned councils, are writing to lodge a formal objection to the current SESRO proposal. While we recognise the importance of securing long-term water resilience, the present scheme raises significant and unresolved concerns relating to cost escalation, safety, environmental harm, land requirements, transport impact, and the fundamental lack of proven necessity. The project, as presented, cannot be supported.

1. Escalating and Unjustified Build Cost
The proposed construction cost has increased dramatically, tripling from £2.2bn at Gate 2 to £6.6bn at Gate 3 and with many major and expensive design changes since Gate 3 now included in the pre-DCO consultation together with inflation pushing up the cost towards £10bn. There has been no transparent explanation, breakdown, or audit-level evidence. Such a huge and sudden escalation raises doubts about Thames Water’s financial modelling, governance, risk forecasting, and capacity to deliver a project of this scale without placing unsustainable costs on customers and taxpayers.

Inflation costs, borrowing costs and a greater understanding of the actual build requirement have all contributed towards a significant increase in overall cost now up to £7.5bn even using Thames Water’s out of date figure. Given Thames Water’s current financial position, the risk of further cost inflation is unacceptably high.

2. Unproven Safety of the Embankments
The reservoir relies on very large earth embankments, yet no comprehensive or independently validated safety assessment has been provided. There have been completely inadequate small-scale tests, and even these have not been disseminated or published in any documents.
There is inadequate information on:
● Embankment failure scenarios
● Consequent flood propagation modelling
● Geological stability
● Long-term settlement and maintenance requirements
Communities living downstream deserve firm, independently reviewed proof of safety before such a structure is even considered. At present, this evidence is not provided, and therefore public safety cannot be assured.

3. Flooding
With regards pluvial and fluvial flooding, the most recent information available, Thames Water can only claim a reduced impact on Abingdon should flooding occur. With a 1 in 5 year risk of flooding being more realistic representation of flood likeness from pluvial and every year from fluvial flooding. Thames Water themselves admit that modelling is incomplete despite decades of planning and cannot guarantee the flooding will not occur. The covering of such a large area of floodplain will require significant alternative land which cannot be accommodated in the current footprint. The reservoir dramatically alters hydrology in the vicinity including the river Ock tributaries.
● The lack of published, independent, high-resolution flood-risk modelling (groundwater + surface + fluvial) leaves open the question: can the floodplain-loss really be offset?
● The success of the mitigation depends heavily on ongoing maintenance and correct operation of drainage/floodplain systems – and that assumes long-term funding and  institutional commitment.
● The risk assessment is complex — with climate change, heavier rainfall, variable groundwater — making any decision provisional.

4. Noise, Pollution, and Long-Term Construction Impacts
The construction period is expected to last many years, yet the documentation underplays the noise, dust, diesel emissions, light pollution, and heavy-plant activity that will be imposed on neighbouring communities. The proposal fails to offer:
● Detailed construction-phase environmental assessments
● A credible mitigation strategy
● A binding commitment to using low-emission machinery
● Binding limits on operating hours
The vague assurances given are insufficient for a project of this magnitude. It is clear that Steventon and Drayton will suffer far more due to the prevailing wind direction and likely see a reduction in air quality during the build phase.

5. Lack of Clarity on Land Requirements
The scheme repeatedly refers to “indicative” land take, with shifting boundary lines and no definitive map of compulsory purchase areas, access corridors, or temporary construction zones. Residents and landowners are unable to understand how they will be affected because Thames Water has not provided:
● A precise red-line boundary
● A breakdown between permanent and temporary land take
● Confirmation of specific land allocation or compensation.
This lack of clarity is unacceptable and prevents meaningful public consultation. Landowners are unable to determine if they are impacted or will be compensated. Indeed East Hanney Parish Council have not been contacted regards compensation, yet it appears that parish land is included in the plans.

6. Increase in Reservoir Size from 100bn to 150bn Litres
The expansion from the previously discussed 100 billion litres to the current 150 billion litres is unjustified and unexplained. A change of this scale fundamentally alters:
● The footprint
● The embankment height
● The environmental consequences
● The risk profile
● The land take
● The long-term operational impacts
No transparent rationale or evidence-based necessity has been provided for this major redesign. The reservoir is therefore inexplicably over sized and therefore stressing the environment with additional land required to compensate for loss of habitat – encroaching on Ardington & Lockinge, West and East Hendred as well as Grove and Drayton. Part of the purported justification was the provision of water to Southern Water via an extremely expensive pipeline on top of the now tripled costs of the reservoir. This has still not been not been approved and there are much cheaper solutions.

7. Unproven Need vs. Alternative Solutions
Thames Water has not demonstrated that SESRO is the most effective, lowest-impact, or best-value solution. In 2024, Thames Water claimed to justify SESRO on the basis that it was £600m to £800m cheaper than the alternative. As the cost estimate increased by at least £4.4 bn in 2025 this clearly questions the validity of this claim.
Several proven alternatives have not been exhaustively or fairly evaluated, including:
● Leakage reduction beyond current minimal targets
● Demand management
● Smart metering
● Water reuse schemes
● Transfers from less stressed regions
● Smaller, distributed storage rather than one supersized reservoir
Until a full, transparent, independent comparative assessment is completed, with full public scrutiny, SESRO cannot be justified.

8. Lack of Transparency on Embankment Height and Visual Impact
Despite repeated requests from communities and local authorities, Thames Water has not provided:
● Accurate, representative visualisations
● Cross-sections showing true embankment scale
● Clear statements on final embankment height
● Verified 3D modelling from realistic viewpoints
The current materials appear deliberately incomplete, making it impossible for the public to understand the real visual and landscape impact of the proposed structure, which would be one of the largest human-made barriers in southern England. The provided material shows indicative and conceptual representation which can be changed at any time. The embankment is just 300m from existing houses in East Hanney.

9. Severe Impact on Local Roads, Access, and Construction Traffic
The proposal lacks a credible transport plan. There is no clarity on:
● Construction traffic routing
● Daily HGV volumes
● Impacts on rural lanes
● Road widening
● New junctions or access tracks
● Safety risks for existing residents
Without a detailed, quantified transport assessment, the traffic and safety impacts of the project remain unknown and unacceptable.

10. Conclusion
For all of the reasons outlined above — spiralling costs, unproven safety, potential flood risk, environmental damage, poorly defined land requirements, inadequate visual and engineering information, severe construction impacts, and the failure to demonstrate genuine need — we object to the SESRO proposal in its current form. Until Thames Water provides independently verified evidence, realistic modelling, transparent costings, full land-use clarity, and an honest comparison with alternative solutions, this project should not proceed.

Signed by the Parish Councils of:
Ardington & Lockinge
Charney Bassett
Drayton
East Hendred
East Hanney
Garford
Long Wittenham
Lyford
Marcham
Steventon
Sutton Courtenay

To read the Group Against Reservoir Development’s objection please visit https://groupagainstreservoirdevelopment.org/gards-objections/