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Received 08/03/2011 Accepted 09/01/2012
Keywords: buildings, structures & design/floods & floodworks/sustainability
This paper shows how an integrated team enabled the UK Environment Agency to deliver a more cost-effective and sustainable solution to improving protection for over 2600 properties in Gainsborough, Lincolnshire, from flooding by the tidal River Trent. The team identified several opportunities to cut costs, mitigate risks and reduce carbon dioxide emissions. At the outset, a detailed condition assessment and numerical analysis of existing flood defence structures enabled many of them to be reused, even though most were originally thought to be at the end of their design life. This and other initiatives resulted in cost savings £10 million, a shorter construction period and significantly lower environmental impact.
1. Introduction
The UK Environment Agency's flood alleviation scheme in Gainsborough, Lincolnshire, improved the condition of the town's defences and reduced annual flood risk to over 2600 properties from a 1:70 annual chance event to a 1:200 annual chance event.
Prior to detailed design, the project appraisal process developed a scheme that would deliver the objectives of reducing flood risk and ensuring integrity of the defences, while giving a cost saving of around £7 million compared to the pre-feasibility estimates for the replacement of life-expired assets. This scheme was then completed with a final overall cost of £16.8 million. This was a further saving of around £3 million against the approved construction phase budget of £19.9 million.
During design and construction, the project team identified further opportunities to refine the scheme and its implementation to enable costs to be reduced and to manage and mitigate risks. This paper summarises the key innovation and best-practice items that were implemented to deliver a sustainable and cost-effective solution to reducing flood risk to Gainsborough.
1.1 Developing the reuse strategy
Gainsborough is on the bank of the lower tidal reach of the River Trent. The town is protected from flooding by nearly 4 km of defences in the form of sheet pile walls, mass gravity walls and earth embankments (Figure 1). This pattern has arisen due to pressures on space along the river from commerce and development. Gainsborough is particularly vulnerable to flooding due to the meeting of tidal and fluvial floodwaters and the low-lying nature of the town...