The increased risk of flooding a massive Abingdon reservoir would cause would result in major local concerns – and not without reason. Any reservoir would have to be sited on flat land at the eastern end of the Upper Thames catchment area.
Watercourses flowing north-eastwards through the area converge here before discharging into the R Thames at Abingdon. Consequently, this area is already particularly prone to flooding during periods of prolonged heavy rain; additional surface water from the Downs would cause watercourses to overflow, thereby inundating homes and highways. These would become even more vulnerable to major flood damage.
To reduce local flood risk, the Environment Agency already advocates a number of measures, including the extension of the area of floodplain south of Marcham; but, as this would become part of the reservoir site, such advice would be impossible to implement.
Currently, most of any reservoir site is productive arable farmland, which is very effective in allowing vegetation to take up surface water. Several thousand acres of farmland would be permanently lost to any proposed reservoir, thereby leading to considerable water run-off from its embankments. To address the sharply increased local flood risk, Thames Water have said in the past they would increase the floodplain area, but any proposed reservoir would itself occupy the area most suitable for it!
In July 2007 the River Ock spilling millions of gallons of water into south Abingdon flooding this Tesco's car park
with hundreds of homes.