As a result of the 2000 floods it was obvious a solution needed to be found. First the Environment Agency produces a Catchment Flood Management Plan. This plan looks at the catchment as a whole and has an action plan that identifies how the impact of flooding can be reduced, through flood warning and control of development, and how the probability of flooding can be reduced through flood defences and land management. If new flood defences are required, a strategy examines options in detail.
The Environment Agency considered these options for Bewdley:
Bewdley Case Study: What solutions have been proposed?
Option 1 - Do nothing
Flooding would continue and get worse. Further banks would collapse, perhaps blocking the river flow, and some properties may be abandoned. Eventually the town may go into decline.
| Total costs | £0 |
| Value of benefit | £0 |
Option 2 - Continued maintenance
Present flooding would continue and worsen, although maintenance of river banks and structures would prevent collapse and blockages.
| Total costs | £0.2M |
| Value of benefit | £0.3M |
Option 3 - Upstream storage
A flood storage dam could be built at Dowles, 1km upstream of Bewdley. However the volume of storage would be restricted, as roads, railway and properties surround the site. In a 1 in 100 year flood the peak flow is 670M3/sec; a storage dam on this site would reduce the river flow to only 650M3/sec, compared with a flow of 325M3/sec needed to prevent flooding in the town.
| Total costs | £15M |
| Value of benefit | £0.5M |
Option 4 - Hard defences in Severnside North and South
Permanent walls along the Severn would be visually intrusive and were opposed by residents. Instead a proposal for demountable defences was put forward, similar to those used elsewhere in Europe for over twenty years. With a height of 2.7m these defences would protect 150 properties from a 1 in 100 year event. When a high flow is forecast the Agency Flood Warning gives at least 24 hours to bring in and put up the barriers.
| Total costs | £6.9M |
| Value of benefit | £7.5M |
Option 5 - Upstream storage and bypass tunnel
This proposal would combine a new dam upstream of Shrewsbury, allowing flooding of farmland in the Severn Valley, and building a bypass tunnel around Bewdley. Four tunnels 6 metres in diameter would be needed to take sufficient of the 100-year flow to protect the town. This proposal would not be environmentally acceptable.
| Total costs | £350M |
| Value of benefit | £0.5M |
Option 6 - Dredging
To be effective the river cross-section would need to be increased by 2 metres from Bewdley to Worcester (50Km), and by 1 metre from Worcester to Gloucester (40Km). Bridges, river walls and quays would need underpinning and the river would need to be constantly dredged to avoid silting up. The environmental impact on flora, fauna and the appearance of the river would be severe.
| Total costs | £68M |
| Value of benefit | £0.8M |
Option 7 - Bypass Tunnel
It would be possible to build a bypass tunnel to take the 100-year flow of 670M3/sec. A 6 metre tunnel would carry about 10% of this flow, so six would be needed to reduce water levels sufficiently. However backwash from the outfall downstream of Bewdley would still lead to significant flooding.
| Total costs | £470M |
| Value of benefit | £0.5M |
The Environment Agency has to make an Environmental Impact Assessment and a cost-benefit analysis.
- The Environmental Impact Assessment looks at likely impacts on residents, wildlife and habitats, water and air quality, cultural heritage, landscape, soils, noise, transport and access.
- The cost-benefit analysis helps decide whether it is worthwhile to undertake a scheme and the best solution.
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1 Comment
Jamie Evans
Guest
09:27 - 21/09/11
In my mind option one is best, as we should not get in the way of the river, as it is nature.
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