Updated 7 Feb 2010

Flooding on the Dorset Stour at Bear Mead

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Flooding on the Dorset Stour at Bear Mead.

Daily graph and 24 hour forcast by the landowner

Flood warning by Peter Colebrook of Marnhull
(18 hours upstream of Bear Mead)

           <------1 day 9h----->
            RAIN           RIVER RISE
       Start    End  mms    Start    End
    

River height

204

at 1500 7 Feb 2010
River state:

FALLING

High

Floodplain state

20%
flooded

River temp: 4°C
River pH:    8.21
Last Flood: 9 Dec 2009
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About the Dorset Stour
Length: 100km, Catchment area: 1,300km2, Population: 400,000, Rainfall: 697-1131 mms/year,
Flood season: Nov-Mar, Land use: 8% urban, 52% arable, 34% grassland, 6% other.
Because much of the river's course is across clay soil, the river's waterlevel varies greatly. In summer, low water level makes the river a diverse and important habitat, supporting many rare plants. In winter, the river often floods, and is therefore bordered by wide and fertile flood plains. Eye Mead floodplain is pasture 1,000 metres wide, and 19 metres above sea level.
When the River floods
Pictures of degrees of flooding at Eye Mead.
0% | 2% | 5% | 10% | 20% | 30%
40% | 50% | 60% | 70% | 80% | 95%
Bear Mead, 1km upstream (right), not visible to photograph.
Floodplain stretches 1km beyond (South) of River

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

FL2197. 18 Jan 2010. 1400 hrs. River height=353. Fields 20% flooded.

Past Records:

Graphs (77 months)
Numbers (77 months)
Location
Display by year
Averages
Statistics

Floods since July 03:

Analysis of Floods
2003 none | 2004 none | 2005 Dec 3 |
2006 Nov 26, Dec 31 | 2007 Mar 6 |
2008 Jan 16, Mar 17, Dec 15 |
2009 Feb 10, Nov 30, Dec 4, Dec 9 |
2010 - |

Report for 7 Feb:

Rain: 0 mms

River:204

Watertable:176

Forcast for 8 Feb:

Rain: 24 hours

River: 190

Watertable: 170

15 Nov - 13 Dec 2009
Heavy rain                       FLOOD-9       -10          -11
14 Dec - 11 Jan 2010

12 Jan - 9 Feb 2010

Future rain:
Rainfall predicted over the next 24 hours by the BBC Weather Centre. The river responds in 24 hours to heavy rain. The river falls equally quickly. Also see: 5-day forcast
Location of Bear Mead:
Bear Mead is about 5 miles North West of Poole Harbour, Dorset, England

BBC Weather Forcast for this area
Work out the probable amount of rain
that will fall, and how it will affect
the height of the river.

5 Day-FORCAST
Hourly-RAIN
Hourly-CLOUD
Hourly-TEMPERATURE
Hourly-WIND
Jetstream

Rule of Thumb:
The difference when stable between height of the Watertable (W) and River (R) decides the response of the River to Rainfall. If (W+60-R) is negative (dry ground), the River will hardly rise even after 30 mms of widespread Rain. If well positive (wet ground), the River may rise 250 cms in 24 hours for 30 mms of Rain. (W+60-R) usually becomes negative about early June and positive again about mid October, conveniently defining the dry season (summer) and wet season (winter). (W+60-R) has been observed with steady values in the range of +100 to -13.

Present value of:

(W+60-R)=

+32

(wet)

A record of the Rainfall, Watertable and River Level of the River Stour at Bear Mead, about 2 miles West of Wimborne Minster, Dorset. Contact the author at for more information.

see also:
TIDAL TRENCH to control flooding.
Unblocking, Tidying, Theory & early results, Results during flooding Mill Stream ditch

This website tries to give simple answers to questions
about flooding on the Dorset Stour at Bear Mead.
  • Where is Bear Mead?
    See Location
  • What do the fields look like when flooded?
    See the pictures below
  • How high does the watertable have to be before the fields flood?
    220 cms
  • How much rainfall is needed to make the river flood?
    About 10 mms rain for every 10 cms below watertable of 220
  • When is it likely to flood?
    When the watertable is about 200 cms
    (but depends how much rain arrives in next 36 hours)

  • How quickly will it flood?
    About 33 hours after heavy rain starts.
  • How quickly will the flood disappear?
    About 48 hours after heavy rain stops.
  • How deep underground is the watertable?
    (220-L) cms where L is the watertable level given above
  • Are there past records for water levels?
    Yes, see Numbers.
  • Are there graphs of how past levels have changed?
    Yes, see graphs.
  • How has the river flow varied since 1968?
    See Flow

State of Flooding on the River Stour

Bear Mead sometimes floods after prolongued rain in the winter. The flood plain is 1200 yards wide at this point. There are spot OS heights of 19 meters, in Field 3 and on the access bridleway "D". The nearest official calibrated river height scale is at Corfe Mullen Mill, 1.5 miles up stream, easily read from the A31. There is a well in Field 5, enabling the water table to be monitored. An unofficial scale has been placed in the river at Field 1. Rainfall is monitored daily at the Author's home, 2 miles away.
The official calibrated river height scale at Julian's Bridge, Wimborne showed 16.9 metres when the river at Bear Mead indicated 150 cms, so Bear mead should flood when the official scale reads 18.6 metres (assuming the weir near Eye Bridge has no effect). Similarly, the scale at White Mill showed 21.4 metres, and should read 23.10 when Bear Mead floods.

These pictures, taken in 2000, show what happens when the floodplain floods. They were taken from Eye Bridge, because it is not possible to get onto Bear Mead itself without a landing craft! The floods usually arrive quickly but also depart quickly, leaving the ground very soggy indeed. The depth of the water-table is a good measure of the "sogginess".

6. The Stour and floodplain.
The Stour and floodplain, winter 2000
8. Approach bridleway to Bear Mead, 15 Nov 2002.
Approach bridleway to Bear Mead, winter 2002
7. Car park at Eye Bridge
The car park at Eye Bridge, winter 2000
Bear Mead 14 Apr 2004
Stour at Bear Mead, looking West
River Stour at normal height in Spring (145 cms)
Stour at Bear Mead, looking East
26 Jun 2009. Thunderstorm over Poole, Dorset. 30mm rain in 9 hours
Thunderstorm, 30 mm rain in 9 hours
26 Jun 2009. Local rain runs into ditch then into river. Hump=250.
millstream enters river

Flood delay in hours

"It takes time for rain which falls over the catchment area to be converted into river flow and any floodwater which builds up takes time to flow downstream to the sea". SWGFL. Bear Mead is 33 hours downstream of rain

Map of Catchment Area

Historic Flood Rainfall Figures:
Source: swgfl
 
Year Month Total Interval Max/Day
           (mm)  (Days)    (mm) 
1894 Dec   141.1   7      36.0 
1916 Nov   134.7   8      29.0 
1916 Dec   104.0   6      44.0 
1933 Feb    89.9   3      56.0 
1943 Feb    94.2   8      26.0 
1954 Dec    84.9   5      27.0 
1966 Nov    68.8   4      56.9 
1979 May   105.6  11      35.0 
1979 Dec    86.1   5      57.8 
1990 Feb    78.0   6      25.0 
1999 Dec    90.9   6      30.5 
2000 Oct    80.2   6      35.0 

Floods recorded on this website:
2005 Dec    30     2      22
2006 Nov    54     4      21
2006 Dec    54     3      27
2007 Mar    53     4      19
2008 Jan    42     3      26
2008 Mar    26     3      16
2008 Dec    20     1      20
2009 Feb    40     2      28
2009 Nov    37     2      23
2009 Dec    38     2      22

Nov-Dec 2009. The number of visitors to this website follows quite closely the height of the river, or perhaps my warning of a flood! If you are one of these users, please email and tell me your interest.
Visitors to flooding website

Compiled, formatted, hyperlinked, encoded, and copyright © 2004, John Palmer, All Rights Reserved.