Carlisle Case Study: What are the current and future flood risks?
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More than 3000 residential and commercial properties are at a 1% annual risk of flooding from rivers within the Eden catchment. The flood risk area includes the A69 Warwick Road, a major highway link to the M6.
A 1% (100 year) annual probability event would lead to a depth of flooding up to 3.5 metres in Carlisle. The areas at risk of flooding are at the confluence of the Rivers Eden and Caldew at Willowholme, and the confluence of the Little Caldew, the River Petteril and the River Eden at Durranhill, Botcherby and Warwick Road. The flood risk results from a combination of both river catchments and two watercourses:
- The River Eden catchment is predominantly rural, covering an area of 2,400 square kilometres
- The River Petteril is one of its major tributaries. the River Petteril catchment is urban and covers an area of 164 square kilometres
- There are two smaller watercourses, the Old Eden and Durranhill Beck, at the eastern end of the flood risk area
Hydrologists believe the sources of the flood risk problems are:
- 50%: flooding from the main river (often the result of development in the flood plain)
- 25%: flooding from surface water and drains, often made worse by blockages and failure
- Flooding from other watercourses (17%) and sewers (8%)
Flooding in the Future
Climate change is predicted to result in changes to flooding in the whole of the UK over the next 50 years. Changes in rainfall patterns could mean that there is an increase in the amount, duration and frequency of rainfall events.
It is very difficult to estimate future large floods reliably, but most scientists consider that climate change is likely to lead to different patterns of rainfall, which might lead to an increase in flood hazards in the UK.
Predictions for the Eden catchment indicate that winter rainfall (and therefore flood flows) might increase by as much as 15 to 20% by 2050, leading to increased flooding in urban areas. Future scenarios will be investigated by the Environment Agency to see the effects on existing flood defences.
As a result of the 2005 flood event, the Environment Agency produced a flood alleviation scheme to reduce the current and future risk of flooding.
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