Lesson learned: Critical services and infrastructure should not be placed in areas that are deemed to be below the 200 year return period (0.5%) flood line.
Case analysis summary:
Heavy rainfall on Friday 7th January 2005 led to flooding in Carlisle, United Kingdom (UK), on Saturday 8th. The rainfall was prolonged over the high ground of the nearby Lake District and Pennines, draining into the River Eden on which Carlisle is situated. This was the worst flood to affect Carlisle since 1822. Across the catchment, the January 2005 flooding affected nearly 2,700 homes in total. In Carlisle three people died, 1,925 properties were flooded and there was significant disruption to residents, businesses and visitors. There was widespread transport disruption with all of Carlisle's buses damaged. The cost of the flooding was estimated at over £400 million.
Carlisle has a town centre located on a flood plain next to the River Eden. Therefore the location has been a critical hub for transport (roads and rail), governance (city council, emergency planning office, blue light services), and business (local and utilities), that were all subsequently impacted by the floods.
As with many British towns, Carlisle has evolved over a number of centuries, with particularly high expansion in the 20th century. It is clear that some of this expansion has severely encroached on the flood plain including the short sighted locational planning of critical services and infrastructure in areas at risk of flooding.
Carlisle has a history of flooding with flood events recorded as far back as the 1700s; prior to the 2005 floods there had been significant floods in 1963, 1968, 1979, 1980, 1984. Carlisle's existing flood defences were built after flooding in 1968, which affected more than 400 properties. This was a 75 year (1.33%) average probability event, considerably smaller than in 2005. In the January 2005 floods the old flood defences were over-topped, resulting in a sudden, dangerous water rise.
A key lesson learned was that a number of elements needed to respond efficiently were flooded and therefore unusable during the event. The following is a quote from 'Carlisle storms and associated flooding Report, Multi-agency debrief report, Executive Summary' (p. 25):
'The early loss of some key pieces of critical infrastructure such as buildings (police and fire station, civic centre), power (Willowholme Sub-station) and communications (landline and mobile), both hampered the handling of the incident and increased the timescale of achieving 'business as normal' conditions.'
It has been reported that the Carlisle flood in 2005 had a return period of 175 to 200 years (0.5%) http://www.geography.org.uk/resources/flooding/carlisle/hydrology. A reasonable conclusion from this case study is that critical services and infrastructure should not be placed in areas that are deemed to be below the 200 year return period (0.5%) flood line.
Photos: Copyright Cumbria Fire and Rescue Service, courtesy of Lee Bosher
The DESURBS project is co-funded by the European Commission within the Seventh Framework Programme under the Security theme.