Cumbria Floods November 2009: An Impact Assessment
Background:
Between Wednesday 18th November and Friday 20th November up to 372mm of rain fell over Cumbria. In the 24 hours ending 00:45 on Friday 20th 314mm of rain fell in Seathwaite. This is a record daily rainfall for the UK. The air mass responsible for this rainfall was formed in south tropics where unusually high sea surface temperatures ensured that the air was particularly rich in moisture. The air mass tracked north as part of a “warm conveyor”. As the air was blown over the Cumbrian fells it cooled causing the moisture to condense and begin to fall as rain. The warm conveyor remained over the fells for a period of 36 hours maintaining a steady downpour resulting in the exceptional rainfall levels. Rain earlier in the week ensured that the ground was already saturated in many areas. Flooding occurred in 5 of Cumbria’s 6 district areas, the only one escaping being Barrow. The effect on properties was concentrated in Allerdale and South Lakeland with most significant infrastructure damage occurring in the former district. Figure 1 below outlines the causes and effects of the heavy rainfall in Allerdale.
Figure 1: Cause and effect of floods in north west Cumbria:
Source: New Civil Engineer (26th November 2009)
Overview:
Records to 6th December 2009 show that a total of 2,239 properties were inundated by flooding with the split falling as follows: 80.1% (1,794) residential; 19.9% (445) commercial. Properties in Allerdale experienced the most flooding (1,721 properties, 76.9% of the total), followed by South Lakeland (402, 18.0%), Eden (79, 3.5%), Copeland (22, 1.0%) and Carlisle (15, 0.7%). These figures are summarised Figure 2 below with figure 3 (flood-related incidents reported to Cumbria Police) giving an indication of concentration of pockets of flooding across the county.
Figure 2: Split of properties inundated by usage and area:
Figure 3: Flood-related incidents reported to Cumbria Constabulary (18/11-22/11/09)
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As noted above properties in Allerdale suffered from the highest levels of inundation. Of the 1,721 properties flooded in the Borough 917 were in Cockermouth. Of these 691 were residential properties. Figure 4 shows predicted flooding in the town (blue shading) against experience (area contained within the red line). Figure 5 shows the extent the morning after the flood peak (Friday 20th November)
Figure 4: Predicted and experienced flooding in Cockermouth:
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Source: Allerdale Borough Council
Figure 5: Cockermouth flooding:
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Source: Environment Agency
