The floods of December2015 in northern England
Name Peter Spencer, David Lindsay, Guy Dixon (JBA), Matthew Parkes
Job title Advisor, Modelling & Forecasting, Inland HydrologyDate 30 August 2016
Aerial photographs © Environment Agency and Peter SmithAerial Photography
What was significant about these events?
17,500 flooded properties
Affected much of northern England
Some locations were flooded more than once
Record 24, 36, 48 hour UK rainfalls
New highest recorded flows in England(~1,700m3/s) on Eden, Lune, Tyne
Highest-ever recorded flows at many rivergauging stations
Some locations had their highest floods in thehistorical record
December 2015 – Flooded Properties
Cumbria & Lancashire
Cumbria 6870
Lancashire 2340
Kendal 2,140
Carlisle 1,930
Keswick 730
Cockermouth 630
Lancaster 360
Croston (on 26th) 340
Total 17,500
How do the December 2015events compare with others?
2015 more widespread & more severe
Properties flooded in Cumbria
2005: 2,500
2009: 2,240
2015: 6,870
December 2015 – Flooded propertiessGreater Manchester Merseyside & Cheshire
Greater ManchesterMerseyside & Cheshire
GMMC 2,500Salford 750
Radcliffe 670
Rochdale area 230
December 2015 – Flooded propertiessYorkshire & Northumberland, Durham, Tees
Yorkshire 5,800(80% in West Yorkshire)
York UA 630
NDT 300
Tadcaster
Mytholmroyd
Leeds
Weather sequence
Northern England - around twicethe normal rainfall in November
By the start of December groundwas wet & lake levels were high
Named storms in December:Desmond (4&5th), Eva (23&24th),Frank (30-31st)
5th & 6th, mainly Cumbria, Lune,Wyre, Tyne
Continuing rainfall in December
On 25th & 26th, mainly Lancashire& Yorkshire
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Rydal Hall - daily rainfalls Nov & Dec 2015
Storm mechanisms
“Warm conveyor” – prolongedmild & moist southwesterlyairstream
Significant orographicenhancement
Prolonged and heavy rainfall
Strong winds (Desmond & Eva)
Storm mechanism in Desmondsimilar to Jan 2005 & Nov 2009
Desmond and Nov 2009 lastedfor around 36 hours
Overview - 5th & 6th December 2015
Affected most of Cumbria (except far west &southwest), and the Lune, Wyre, Tyne
Serious flooding in Carlisle, Cockermouth,Kendal, Keswick, Lancaster – and many villagesin NW & NE England
New flood defences overtopped at Carlisle,Keswick, Cockermouth
Wyre Flood Storage Basins completely filled
57 Severe Flood Warnings issued for Cumbria &Lancashire
Rainfall - 5th & 6th December 2015
Rainfall : 5th & 6th December 2015
Station Catchment \Town
12 hour 24 hour 36 hourRainfall
(mm)ReturnPeriod
Rainfall(mm)
ReturnPeriod
Rainfall(mm)
ReturnPeriod
Northwest
Skelton Eden 75 130-150 138 >1000 183 >1000
Thirlmere u/s Keswick 196 >1000 325 >1000 401 >1000
Honister Derwent 209 250-600 341 >1000 367 >1000
Kentmere u/s Kendal 106 25-75 183 60-100 225 100-200
Turnerford Lune 68 20-30 110 75-100 137 150-300
Abbeystead Wyre 66 10-15 97 20-40 115 25-60
Northeast
Chirdon North Tyne 56 30 94 100 122 180
Garrigil South Tyne 112 130 151 160 179 180
Overview - 25th & 26th December 2015
Rainfall less than 5th & 6th DecemberLancashire and Greater Manchester - mainly theRibble, Douglas, Roch & Irwell catchmentsYorkshire – mainly Calder, Wharfe, Aire, Ouse
FloodingLancashire - Ribchester & Whalley, St Michaels,Wigan and CrostonGreater Manchester – Radcliffe, Rochdale, SalfordSome part of Cumbria (again)Calderdale (Mytholmroyd, Hebden Bridge),Tadcaster, York, parts of Leeds
Rainfall - 25th & 26th December 2015
Rainfall : 25th & 26th December 2015
Raingauge Catchment 12 hour 24 hour 36 hourRainfall
(mm)ReturnPeriod
Rainfall(mm)
ReturnPeriod
Rainfall(mm)
ReturnPeriod
Northwest
Great Harwood Ribble 61 18 95 89 103 75
Common Bank Douglas 53 15 73 30-40 81 30-40
Holden Wood Irwell 71 25-35 109 50-120 128 50-160
Cowm Res Roch 70 15-20 107 40-70 116 30-50
Northeast
Scargill Nidd 42 4 77 20 82 15
Thruscross Wharfe 55 10 102 60 108 45
Hydrometric aspects – flow stations
In Cumbria & Lancashire42 stations had faults, 32 of thesefloodedRecovered most peak levelsmissed in the event
Improve peak flow estimates by:Use of modelled top-end ratingsConsistency between stations alongthe same watercourse
Uncertainties remain due to:Inability to gauge such eventsInability to measure floodplain flowsChanges in channel morphology
Gauging stations with highest ever flow inDecember 2015
NE 25-29th Dec
NW Dec
NE 5&6th Dec
Rivers : 5th & 6th December 2015River Station Rank Peak flow
(m3/s)Peak as ratio
of QMEDIndicative
return period
NorthwestEamont Pooley Bridge 1 268 4.45 350Petteril Harraby Green 1/2 110 3.26 175Caldew Cummersdale 2 279 1.75 20Eden Sheepmount 1 1900 3.09 300Greta Low Briery 1 350 3.15 175Derwent Ouse Bridge 1 450 4.36 500Derwent Seaton Mill 1/2 600 2.93 300Kent Victoria Bridge 1 403 2.80 150Leven Newby Bridge 2 224 3.09 150Lune Caton 1 1740 2.39 100NortheastTyne Bywell 1 1730 2.04 95-190South Tyne Haydon Bridge 2 915 2.02 50-80North Tyne Reaverhill 2 716 2.12 50-75
Rivers : 25th & 26th December 2015River Station Rank Peak flow
(m3/s)Peak as ratio
of QMEDIndicative
return period
Northwest
Yarrow Croston 1 79 2.34 150
Calder Whalley Weir 1 501 2.94 450
Roch Rochdale 1 93 2.13 80
Roch Blackford Bridge 1 192 2.67 150
Irwell Irwell Vale 1 177 2.04 70
Irwell Bury Ground 1 284 2.54 100
IrwellManchesterRacecourse
1 500 1.86 50
Northeast
Nidd Hunsingore 1 297 2.47 80-100
Calder Mytholymroyd 1 276 3.26 100+
Ouse Skelton 2 544 1.69 40-50
Aire Armley 1 350 2.49 200+
Aire Lemonroyd Weir 1 266 1.72 30-50
Wharfe Tadcaster 1 480 2.23 100
Catchment rainfalls and flood volumes
Return periods of raingauge data higher than riversBut averaged rainfall return periods over large catchmentsgenerally similar to river return periods
River Station Rainfallreturn period
River returnperiod
Eden Sheepmount 170 300
Derwent Seaton Mill 220 300
Lune Caton 230 100
Douglas Croston 140 150
Flood volumes
With initially wet catchments and long duration storms,flood volumes and percentage runoffs were very high.Many percentage runoffs in Cumbria were around 90%.
North west EnglandAMAX where maxima on 5&6th December
North west EnglandAMAX where maxima on 25&26th December
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Irwell at Manchester RacecourseAnnual Maxima (provisional) from 1941
Appleby
Historical flooding76 floods from 1800 to 19761.7m above previous gaugedhighest (Jan 2005)442m3/s, ~return period 200Flooded properties:
Dec 2015: 176Nov 2009: 4Jan 2005: 53
One location was flooded threetimes in December
Eden at Carlisle : Highest events from 1848
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Flood Alleviation Schemes built at Carlisle, Keswick,and Cockermouth after the 2005 & 2009 floods.
Design return periods were quoted as 200, 75, and100 years respectively.
All three schemes were overtopped in 2015.
Detailed flood estimates made using the standard UKFlood Estimation Handbook (FEH) with updates.
Statistically, the chance of such events is pretty remote
So are our methods up to the job?
Questions after the events on 5&6th Dec 2015
1. Are there factors leading to:Short-term “bunching” of flood peaks
Long-term changes affecting flooding
2. Should we make more use of long-termapproaches such as historic data & continuoussimulation?
Questions after the events on 5&6th Dec 2015
Questions after the events on 5&6th Dec 2015
3. FEH methods - The statistical methods in theFEH can use data from anywhere in the UK.
Should methods make more use of local data?
Do we select the right stations?
A pooling group should behydrologically similar
Stations are selected forpooling groups mainly oncatchment area & SAAR
So selected stations can havevery different floodcharacteristics (e.g. QMED)
And very differentpermeabilities (SPRHOST)
4. Are very large floods different?Flood runoff?
Flood routing?
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Example lake routing
Questions after the events on 5&6th Dec 2015
5. Is Cumbria different?Is transfer of flood data fromother locations appropriate?
Are rainfalls different?
Is Cumbria showing the effectsof climate change first?