Updated 11 Aug 2012

Flood on Dorset Stour 09 Jul 2012

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Flood on Dorset Stour 09 Jul 2012.

The average rainfall in Dorset for June 1991-2011 was 51 mms. Between 04 June - 08 July 2012 Dorset experienced 281 mms in 34 days, an increase to 550%. This caused a flood of the Dorset Stour 08-10 July, "higher than any recorded before" (average 106%) at 9 of 11 monitoring stations run by the Environment Agency on that 70 mile river. Statistics made public online by E.A. are shown below, together with graphs of river levels permitted by E.A. The direct cause of this increase is a move of the summer jetstream over the UK from North of Scotland to over Spain, allowing a series of low pressure areas to pass over England. Something similar happened in 2007. Rain surges #15 to #20 passed down the Stour between Gillingham and Throop, followed by #21 on 08jul2012 which produced the unusually high flood. At Bear Mead, the flood plain stretches 800 metres South of river and 1000 metres North. Most of this is rated at 1 in 100 chance of flooding each year by Environment Agency. 60 hours after a peak of about 390, the river level at Bear Mead was down to 240, and most of the surface water had drained away or was hidden in the dense well-watered summer vegetation, leaving a cloud of summer brown butterflies fluttering in the sunshine. The increased rainfall in summer also caused overgrowth of grass, nettles and plants like poison hemlock, musk mallow and oxeye daisy.
1. Jetstream.. 2. Flooding.. 3. Levels and rainfall.. 4. Monitor stations.. 5. Flood progress.. 6. Statistics.. 7. Photos.. 8. 2007 levels.. 9. Floodplain...
Other floods: 03dec2005 | 26nov2006 | 16jan2008 | 10feb2009 | 01may2012
1. The jet stream has shifted further south than usual, bringing wet and windy weather to the south of the country, making summer 2012 similar to summer 2007.
See Jetstream forecast for 16 days

2. View of flood

The Dorset Stour floodplain, pictures centred on Eye Mead, SY 995-995, Eye Bridge left foreground, (see degrees of Flood).

FL3224. 09 Jul 2012. 0900 hrs. River height=390. Fields 100% flooded. (Very high summer flood, after 100mms rain in 7 days)

3. Rainfall, river and groundwater levels at Bear Mead 2012

See also 2007
02 May 2012 - 30 May 2012
-14
31 May 2012 - 28 Jun 2012

29 Jun - 27 Jul 2012
123456789012 FLOOD-15
Rainfall measured near Bear Mead, in mms per 24 hours, causing the river surges 14-23 shown above. Surge 21 is the flood of 9 July 2012 shown below.

 Surge 14 
          
03may  6.8
07may  3.5
08may  2  
09may  9  
10may 25.5
----- ----
11may 46.8

 Surge 15 
          
04jun  2.5
05jun 14.5
06jun  3.6
07jun 23  
08jun  8.5
----- ----
09jun 52.1

 Surge 16 
          
          
          
          
10jun  5  
11jun 33  
----- ----
12jun 38  

 Surge 17 
          
          
          
          
12jun 13  
15jun  7.5
----- ----
16jun 20.5

 Surge 18 
          
          
          
18jun  1.5
21jun 19.3
22jun  3.5
----- ----
23jun 24.3

 Surge 19 
          
          
          
          
          
24jun 18.5
----- ----
25jun 18.5

 Surge 20 
27jun  1  
29jun  2.8
30jun  2.9
02jul 16.4
03jul 12.7
04jul 15  
----- ----
05jul 71.6

 Surge 21 
          
          
          
06jul  5.5
07jul 32  
08jul 18  
----- ----
09jul 55.5

 Surge 22 
          
          
          
10jul  4.5
12jul 14  
13jul  3.5
----- ----
14jul 22  

 Surge 23 
          
          
          
          
15jul  1  
16jul  3  
----- ----
20jul  4  

4. Monitor Stations

Monitor Stations along the Dorset Stour (run by Environment Agency) used in this report. See more details.

5. Flood progress along river

These 6 graphs show the progress of the peak flood along 57 miles of the Dorset Stour in 35 hours between Gillingham and Throop, as it passes by Monitor Stations run by the Environment Agency. Each graph "Contains Environment Agency information © Environment Agency and database right"

7.22
miles
to
source

Gillingham peak of 2.03 metres at 0600 hrs on 08jul2012

4
hrs
total

4
hours
delay

21.13
miles

21.13
total

1/1,250
gradient

Hammoon peak of 3.26 metres at 1000 hrs on 08jul2012

9
hrs
total

5
hours
delay

10.76
miles

31.89
total

1/1,749
gradient

Blandford peak of 2.30 metres at 1500 hrs on 08jul2012

18
hrs
total

9
hours
delay

11.92
miles

43.81
total

1/1,476
gradient

BM 21




High water
at
BEARMEAD
expected

0300 hrs
09jul2012

390?

21
hrs
total

3
hours
delay

3.23
miles

47.04
total

1/1,533
gradient

Wimborne peak of 1.78 metres at 0600 hrs on 09jul2012

29
hrs
total

8
hour
delay

6.92
miles

53.96
total

1/1,985
gradient

Ensbury peak of 3.37 metres at 1400 hrs on 09jul2012

35
hrs
total

6
hour
delay

3.39
miles

57.35
total

1/1,364
gradient

Throop peak of 1.79 metres at 2000 hrs on 09jul2012

7.38
miles
to
sea

6. Flood statistics


See other Travel Times for 2011-12


                      FLOOD STATISTICS

     Monitor    Peak      Peak Peak  Previous       Site     Site River
ID   Location   Date      Time Meter Highest        Opened   AOD  Length Gradient
3298 Wincanton  08jul2012 0200 1.51  2.94 13dec2008 Jan 2004 67.5
3297 Milton     08jul2012 0200 1.03  1.03 09feb2009 Jan 2003  -
3308 Colesbrook 08jul2012 0500 1.65  1.58 09jul2009 Dec 1973 71.8 metres
3296 Gillingham 08jul2012 0600 2.03  1.95 10feb2009 Jan 1992 68.1 34,005 1/1,250
3307 Lodden     08jul2012 0600 2.95  3.46 10jan2007 Jan 1992 68
3306 Hammoon    08jul2012 1000 3.26  3.11 02dec2005 Mar 1968 40.9 17,317 1/1,749
3305 Blandford  08jul2012 1500 2.30  2.27 03dec2005 Jan 1991 31   19,183 1/1,476
---- BEAR MEAD  09jul2012 0300 3.90? 3.85 03dec2005 Aug 2003 18    5,198 1/1,533
3302 Wimborne   09jul2012 0600 1.78  1.67 03dec2005 Jan 1997 14.6 11,137 1/1,985
3295 Ensbury    09jul2012 1400 3.37  3.08 03dec2005 Jan 1992  9    5456  1/1,364
3303 Throop     09jul2012 2000 1.79  1.56 11feb2009 Jan 1973  5
3304 Loverly    08jul2012 1000 0.33  0.75 05dec2009 Jul 1973 37.3
3299 Walford    08jul2012 0800 0.40  0.60 11mar2007 Nov 1974 18.7
3301 Hurn       08jul2012 2100 1.21  1.38 10feb2009 Jun 1989  4.5
3300 Iford      10jul2012 0300 2.48  2.34 04dec2005 Jan 2006  -
Source: Environment Agency

7. Local photos

FL3220. Flooded bridleway to A31, 760 yards from river Stour.
FL3225. Trapped herd of 36 bullocks, 700 yards from nearest road.
HEML3185. Overgrowth of grass and poison hemlock.
FL3209. Overgrowth of musk mallow and oxeye daisy.

8. River and groundwater levels at Bear Mead in 2007

Jetstream patterns and causes in 2012 seem similar to June-Aug 2007.
See www.bbc.co.uk/news/science-environment-18783422 and 2012
See other levels for 2003-2012
31 May - 28 Jun 2007

29 Jun - 27 Jul 2007

28 Jul - 25 Aug 2007

See June 2007 and July 2007 for rainfall over 24 hours in mms.

9. Floodplain around Bear Mead

Flood plains prone to flooding around Bear Mead. Up to 800 metres South and 1000 metres North of river.
Several islands stand above likely flooding North of the river, but none in South up to A31
Scale 15,000:1. Dark blue: 1 in 100 chance of flooding each year. Light blue: 1 in 1,000 chance.

Compiled, formatted, hyperlinked, encoded, and copyright © 2012, John Palmer, All Rights Reserved.