STORM DESMOND

Storm Desmond was low pressure system (939mb at its lowest) which formed on 4th December

2015 and dissipated on the 8th December. Its path took across Atlantic Ocean and its centre

passed well to the North of the UK.

Position of storm Desmond Friday 4th December

Source: Met Office

Whilst the storm centre passed well to the north, Desmond was notable for directing a plume of

moist air, known as an “atmospheric river” to the UK. These are areas of very moist air that are

typically several thousand kilometres long and a few hundred kilometres wide. The amount of

water vapour in these systems is huge and can be more than the flux of the Amazon River. It was

this body of very moist air that produced the extreme levels of rainfall.

Satellite image of Atmospheric River brought to the UK by Storm Desmond

Source: National Weather Service

The strong winds from Storm Desmond dragged moisture rich air over Cumbria where the

mountain terrain forced the air upwards, leading to cooling of the air, condensation of the water

vapour and therefore very intense rainfall. Radar animation from the Met Office has shown how

the heaviest rain was concentrated in over Cumbria for an extended period as winds from the

storm swept over Northern Ireland, Northern England and Scotland.

RAINFALL

The nature of the storm meant that the rainfall was concentrated in a relatively small area where

the local terrain forced moisture rich air upwards. This is known as “relief” or “orographic” rain –

which by its nature can lead to highly concentrated episodes of intense rainfall.

A gauge at Honister Pass recorded 341.4mm of rainfall in the 24-hours up to 1800 GMT on 5

December 2015, making for a new UK record for any 24-hour period. This beat the previous

record of 316.4mm set in November 2009 at Seathwaite, also in Cumbria.

A new 48-hour record (from 0900 to 0900 hrs) was also set, when 405mm was recorded at

Thirlmere in Cumbria in just 38 hrs.

Met office rainfall data for Storm Desmond

Source: Met Office

STORM WINDS

In addition to the record rainfall the storm also produced very high winds as shown in the table

below. Gusts of over 80 mph were experienced in more exposed locations, with the strongest

recorded gust of 99 mph at Great Dun Fell, a high level site in Cumbria at 2,880 feet.

The table below lists the locations of the highest wind speeds.

Storm Desmond Maximum Wind Speeds

Site Name Area Max Gust Speed

Capel Curig Gwynedd 81

Needles Old Battery Isle of Wight 78

High Bradfield South Yorkshire 77

Redesdale Camp Northumberland 73

Loftus Cleveland 70

Aberdaron Gwynedd 69

Charterhall Berwickshire 68

Valley Gwynedd 67

Source: Met Office

RIVERS

The intense rainfall in a short period of time onto already saturated ground led to rapid surface

run-off into the rivers causing a number of record river levels being recorded as follows:

Record River Levels from Storm Desmond

Source: Environment Agency

In many instances in Cumbria, river levels were at all-time record levels and were therefore able

to overtop flood defences which had been put in place following previous floods, notably in 2005.

Further details in relation to the affected towns their rivers are provided below.

POWER OUTAGES

A combination of high winds and flooding led to power cuts affecting around 60,000 people. The

vast majority of these were in Lancaster, where the Caton Road substation was inundated by a

metre of water. A breakdown of all the affected areas is shown below:

Power Outages resulting from Storm Desmond

Source: Electricity North West

Carlisle (Postcodes: CA1, CA2, CA3, CA4, CA5, CA6)

River Eden

River Eden height data

Source: www.riverlevels.co.uk

The river Eden is also fed in Carlisle by the rivers Caldew and Petteril and both of these tributaries

recorded their highest ever levels on the 6th December. The peak levels in Carlisle were around

9.15 am on Sunday 6th December

Improved flood defences were completed in 2010 at a cost of £38m including raised defences,

two new pumping stations, 30 flood gates, two raised footbridges and seven CCTV cameras.

Despite this investment, the flood defences were overtopped as follows:

Rivers Eden and Petteril at Carlisle City Centre, Botcherby and Warwick Road areas

Rivers Caldew and Eden at Carlisle, Willowholme, Caldewgate and Shaddongate (north of Caldew

Bridge, A595)

River Eden at Carlisle Rickerby Village.

River Caldew at Carlisle, Viaduct Estate Road area

Rivers Caldew and Eden at Carlisle, Willowholme, Caldewgate and Shaddongate (Note, South of

Caldew Bridge, A595)

The normal level of the Eden at Sheepmount, Carlisle in average weather conditions is between 0.69m and 2.14m.

The usual range in more extreme weather conditions is between 0.63m and 3.45m. It has been between these levels for 90% of the time since monitoring began.

Desmond produced the highest ever height recorded of 7.8m on 6th December

Key: Low, average & high levels Typical High level Typical Low level

Cockermouth (Postcode: CA13)

River Derwent

River Derwent height data

Source: www.riverlevels.co.uk

Cockermouth is situated where the River Cocker flows into the River Derwent. On the 5th

December the Cocker reached a peak height of 4.04 meters. Its typical high level is 1.5m,

indicating the extreme nature of this event.

Cockermouth suffered extensive flooding in 2009. Improved flood defences were completed in

2013, which included the UK’s first self-closing flood barriers. Whilst the defences worked as they

should, they were not designed to cope with the extreme river levels noted above and were

overtopped at around 7pm on the 5th December.

Source: BBC Source: Guardian

The normal level of the Derwent at Kingfisher, Cockermouth in average weather conditions is between 0.58m and 0.72m.

The usual range in more extreme weather conditions is between 0.50m and 1.40m. It has been between these levels for 90% of the time since monitoring began.

Desmond produced the highest level ever recorded of 4.52m 6th December. The previous highest level was 2.7m in 2012

The highest level ever recorded at the Cocker at South Street Footbridge is

4.97m, recorded on Thursday 19th November 2009 at 10:30pm

Key: Low, average & high levels Typical High level Typical Low level

Keswick (Postcode: CA12)

River Greta

River Greta height data

Source: www.riverlevels.co.uk

Flood defences were designed to withstand 15ft (4.57m), the height reached in the 2009 floods.

These were completed in 2012 at a cost of approximately £6m. The main feature was a flood wall

topped with reinforced glass panels. Unfortunately, Storm Desmond produced a height of 17.5

feet (5.35m) which therefore significantly exceeded the height of the defences.

Keswick flood defence wall and wall being overtopped

The normal level of the Greta at Greta Bridge in average weather conditions is between 0.99m and 1.53m

The usual range in more extreme weather conditions is between 0.95m and 3.00m. It has been between these levels for 90% of the time since monitoring began.

Desmond produced the highest level ever recorded of 5.35m on 6th December. The previous high level was 4.66m in 2009.

Key: Low, average & high levels Typical High level Typical Low level

Appleby (Postcode CA16)

River Eden

River Eden at Appleby height data

Source: www.riverlevels.co.uk The River Eden flows through the centre of Appleby and breeched defences on the morning of

5th December. The water level rose rapidly and in a matter of minutes rose from a few inches to

over 3 feet.

Flooding in Appleby

Source: BBC

The normal level of the Eden at Appleby in average weather conditions is between 0.13m and 1.09m

The usual range in more extreme weather conditions is between 0.25m and 1.80m. It has been between these levels for 90% of the time since monitoring began.

Desmond produced a record high level of 4.69m on 5th December. The previous high was 3.54m in 2011.

The highest level ever recorded at the Eden at Appleby is 4.40m, recorded on Saturday 8th January 2005 at 4:15am. 4.69 5/12

Key: Low, average & high levels Typical High level Typical Low level

Windermere/ Ambleside/ Bowness (Postcodes: LA22, LA23, LA12, LA11)

Level of Lake Windermere at Far Sawrey

Source: www.riverlevels.co.uk

Winderemere Flooding Bowness-on-Winderemere

Source: Westmoreland Gazette/ D Shortt Source: BBC

The normal level of the Lake Windermere at Far Sawrey in average weather conditions is between 0.35m and 0.59m.

The usual range in more extreme weather conditions is between 0.23m and 0.99m. It has been between these levels for 90% of the time since monitoring began.

Desmond produced a height of 2.82m on 6th December. The previous highest level recorded was 2.9m

Key: Low, average & high levels Typical High level Typical Low level

Kendal (Postcode LA8, LA9) River Kent

River Kent height data

Source: www.riverlevels.co.uk

The River Kent is the England’s fastest flowing river. Flood defences in Kendal were constructed in

the 1970s and whilst upgrades have been planned, these have not been implemented due to

central government funding shortages. The defences in the town of Kendal were overtopped on

the afternoon of 5th December however defences at the electricity sub-station did hold,

protecting power supplies.

Flooding in Kendal

Source: thebay.co.uk Source: BBC

The normal level of the Kent at Victoria Bridge in average weather conditions is between 1.21m and 1.62m

The usual range in more extreme weather conditions is between 1.20m and 2.30m. It has been between these levels for 90% of the time since monitoring began.

Desmond produced a record high level of 3.86m on 5th December. The previous high was 3.40m in 2005.

The highest level ever recorded at the Kent at Victoria Bridge is 3.40m, recorded on Saturday 8th January 2005 at 2:15am. NEW HIGH 3.86 5/12

Key: Low, average & high levels Typical High level Typical Low level

Lancaster (LA1)

River Lune

River Lune Height Data at Caton (upstream of Lancaster)

Source: www.riverlevels.co.uk

Flood warnings for the River Lune were issued around 4pm on Friday 4th December and a flood

alert for the flood plain was issued at 1pm on Saturday 5th. The river Lune reached record levels

at 8.45pm on Saturday - at peak times the river was carrying 1,670m3 of water a second (by

contrast, the usual discharge for the Thames is 66m3/ second).

Lancaster Flooding

Source: Daily Mail Source: Lancaster Guardian

The normal level of the Lune at Caton in average weather conditions is between 0.32m and 1.54m

The usual range in more extreme weather conditions is between 0.28m and 3.20m. It has been between these levels for 90% of the time since monitoring began.

Desmond produced the highest level ever recorded at 7.95m on 6th December. The previous high was 5.83m, reached in 2011.

The highest level ever recorded at the Lune at Caton is 7.06m, recorded on Tuesday 31st January 1995 at 9:15pm. 7.95M 5/12

Key: Low, average & high levels Typical High level Typical Low level