Reservoir Summary June 2025

History and approvals

 A 100 million cu.m reservoir was rejected by the 2010 Public Inquiry, it is now 150 million cu.m with increased land take; this increase is in spite of measures to reduce usage by household water metering, the Government Water Framework Directive and publicity to reduce leakage and personal use, and even when planning for population growth In 2010 the Inspector specifically ruled there was no case for a large reservoir. (Alternatively water could be transferred from the River Severn, a more drought resilient source than the Thames)

The DEFRA Secretary and the Chancellor sanctioned the further development of proposals in August 2024 and January 2025 respectively. Formal Government consent requires a Development Control Order currently programmed for early in 2027. An Order will not tackle need, and only the scrutiny of a Public Inquiry would tackle this. To this end SaferWaterS (a GARD sister company) and CPRE have managed to convene a High Court Judicial Review seeking an Inquiry. The review will be held on 25 and 26.June with a decision in July.

Environmental impact

The 150 million cu.m reservoir consumes a large area of the existing flood plain, its bunds are 10km long, and between 15 and 23 metres high, high enough to be visible from afar and cast long shadows across a predominantly flat and open landscape. It is close to existing villages, a field or so away from Steventon, Drayton and East Hanney.

And then there is the impact upon the natural environment, for example watercourses are diverted and hedgerows, field patterns and over 200 recorded Ancient and Veteran tress lost and with many red–listed species threatened through habitat loss.

All plus the imposition of the reservoir structure itself and its extended infrastructure, both permanent and during 10 years of construction.

Flooding history

Flooding is commonplace in the vicinity. In November 2024 Storm Bert caused havoc with roads and schools closed, trains cancelled, etc. There were numerous Section 19 reports of house inundations locally, notably in the Hanneys, Steventon and Sutton Courtenay. Also over a 35-hour period raw sewage was discharged to the flooded Letcombe Brook, which runs through East Hanney, caused by stormwater infiltration overloading the Wantage sewage works.

To summarise flooding is an enduring threat to the area and the Met Office predicts that climate change will produce more frequent and severe storms over the coming years.

Reservoir impact upon flooding

 The reservoir would cover and seal over large areas of the flood plain and there are well founded doubts that sufficient compensation for this fluvial flooding could be found. This flood plain is significant, for example the sources of Letcombe and Childrey Brooks are significantly higher than the low lying Hanneys through which they flow. At a 2024 meeting Thames Water advised that no new modelling of fluvial flooding had been carried out.

The water table is extremely high and the reservoir would obstruct its main flow heading to the River Ock to the North. At a County Council and VWH D.C meeting held in February 2024 Thames Water verbally advised the possibility of a 1 metre rise in the groundwater level, but extraordinarily this was not minuted. A groundwater drain to the River Ock was added at that time (alarmingly late). If insufficient this would be devastating to the South and East (Steventon, East Hanney and Drayton).

Originally a 20 metre high trial embankment was proposed, the current test (CCT) is a mere 3 metres high and a larger scale embankment test will only follow after Development Consent. This seems very late in the process should problematic and/or costly ground conditions be met

Extraordinarily dam break analysis was to be carried out late in construction, but following pressure from the Environment Agency and Councils this will take place to obtain a DCO.

In an emergency draw down it is necessary to reduce the water level by 1 metre a day or 76cu.m/second. During the winter floods the flow gauge downstream of Culham Lock was measuring 210cu.m/second with the lock overtopped and the road flooded at Sutton Bridge (the mean flow at the gauge is 28cu.m/second). Therefore any addition to these flows (which might well coincide with high rainfall) would have catastrophic effects starting

• Where the 6 metre diameter intake/outfall tunnel meets the Thames at the Culham Cut immediately to the North of Steventon.
• Where the stormwater drain meets the River Ock.
• And far beyond.

Conclusion

Should a case for a new reservoir be proven then it seems clear that it is in the wrong location, threatening an already fragile natural and built environment.

Sources

Thames Water texts and plans

GARD (Group against Reservoir Development) newsletters, etc

Papers by Professor Binnie

Flood Summit, 10 April at East Hanney

Parish Council meeting minutes