Banbury flood management scheme
An £18.5 million storage reservoir beside the M40, opened in 2012, holds back the River Cherwell to keep Banbury dry.
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Evidence
9 figures, each threaded to its source
Cost of the scheme
18.5 millionGBP
3 sources
“In 2012, an innovative project was completed to construct a flood storage reservoir north of the town at an investment of £18.5 million.”
Flood storage reservoir capacity
3 millioncubic metres
2 sources
“The scheme involved building a 3-kilometre-long and 4.5-metre-high embankment, paralleling the M40 motorway, to form a 3 million cubic meters storage basin.”
Length of the earth embankment
3km
2 sources
“The scheme involved building a 3-kilometre-long and 4.5-metre-high embankment, paralleling the M40 motorway, to form a 3 million cubic meters storage basin.”
Houses protected by the scheme
441houses
2 sources
“441 houses and 73 commercial properties are protected from flooding”
Damage caused by the 1998 flood
12.5 millionGBP
“The 1998 flood led to the closure of the railway station and caused £12.5 million in damage.”
Estimated long-term benefits
100 millionGBP
“The benefits are estimated at over £100 million.”
Earth used to build the embankment
100,000tonnes
“Around 100,000 tonnes of earth were required to make the embankment”
Height of the earth embankment
4.5metres
2 sources
“The scheme involved building a 3-kilometre-long and 4.5-metre-high embankment, paralleling the M40 motorway, to form a 3 million cubic meters storage basin.”
Commercial properties protected
73commercial properties
2 sources
“441 houses and 73 commercial properties are protected from flooding”
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Background
Banbury sits in the narrow valley of the River Cherwell in Oxfordshire, with much of the town built on the floodplain. When long spells of rain fall on the catchment upstream, the river rises quickly. In 1998 floodwater closed the railway station and caused £12.5 million of damage, and the town flooded again in 2007. The Environment Agency's answer was one of the largest flood storage schemes in England, finished in 2012 at a cost of £18.5 million. A 3 km earth embankment up to 4.5 metres high runs beside the M40 north of the town, turning farmland into a reservoir that can hold about 3 million cubic metres of floodwater and release it slowly once the peak has passed. The A361 was raised so the main road stays open, flow control structures manage the river, and a pumping station moves water out of the town. The scheme protects 441 houses and 73 commercial properties, and its long-term benefits are put at over £100 million.
Causes
A town on the Cherwell floodplain
Banbury grew up beside the River Cherwell, and homes, shops, the railway station and industrial estates spread across the flat valley floor. Land that a river naturally floods was covered in buildings, so even a moderate rise in the Cherwell put hundreds of properties and the town's transport links under water.
A catchment that fills quickly
The Cherwell drains a large area of countryside upstream of Banbury, and the narrow valley funnels runoff towards the town. After prolonged rain the ground saturates and water reaches the river rapidly, while roads, roofs and car parks inside the town add fast urban runoff, so flood peaks arrive quickly.
Repeated damaging floods
The 1998 flood closed the railway station and caused £12.5 million of damage, and further flooding hit the town in 2007 during a summer of heavy storms across England. Repeated losses on this scale made the economic case for spending £18.5 million on permanent protection.
Effects
Primary
- 441 houses and 73 commercial properties are protected from flooding.
- The reservoir can store about 3 million cubic metres of floodwater and release it slowly.
- The raised A361 keeps the main road into town open during a flood.
Secondary
- Flood damage, insurance claims and transport disruption have fallen sharply.
- Businesses and developers have more confidence to invest in the town.
- Downstream flood peaks on the Cherwell are lower because water is held back and released gradually.
Social
- Residents no longer face evacuation and months of drying out after a flood.
- Anxiety in wet winters is reduced for people living on the floodplain.
- New footpaths and green space around the storage area give locals somewhere to walk.
Economic
- The scheme cost £18.5 million but its benefits are estimated at over £100 million.
- The town avoids repeats of 1998, when flood damage cost £12.5 million and shut the railway station.
- Farmland inside the storage area still floods deliberately, so its farming value is reduced during flood events.
Environmental
- Borrow pits dug for embankment earth became ponds, and trees and hedgerows were planted to create new habitat.
- A large artificial embankment now runs across the valley landscape.
- Storing floodwater and releasing it slowly reduces bank erosion downstream.
Responses
Immediate
- Flow control structures on the Cherwell divert rising floodwater into the storage reservoir during heavy rain.
- A pumping station moves water out of the town when levels are high.
- The Environment Agency issues flood warnings for the Cherwell valley.
Long term
- The £18.5 million scheme, completed in 2012, built a 3 km embankment up to 4.5 metres high to create the flood storage reservoir.
- The A361 was raised so the road stays open during floods.
- Around 100,000 tonnes of earth were moved to build the embankment, with the borrow pits landscaped into ponds and habitat.
- The reservoir and its structures are inspected and maintained so the scheme keeps working for decades.
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