Blake Lapthorn solicitors' Climate Change team held a green breakfast on flooding in the Solent on 16 October 2012.

1. Flooding and sea-level rise
in the Solent Region
Robert J. Nicholls
Faculty of Engineering and the Environment
University of Southampton
r.j.nicholls@soton.ac.uk
South Coast green breakfast series

2. Plan
• Global sea-level change
– Historic
– Future (scenarios)
• Relative sea-level change in the English
Channel
• Flooding in the Solent
– Historic flood analysis
– Flood modelling

3. < 1mm/year
6mm/year
> 20mm/year

4. Global sea-level rise
(IPCC, 2007, AR4 WG1))

5. Recent global sea-level rise
(IPCC, 2007, AR4 WG1)
• Sea-level rise 1961-2003
1.8 mm/year compared with less than
1mm/year over the last 8000 years.
• Sea-level rise 1993-2003
3.1 mm/year, but only 10 years !

6. Global sea-level rise
(IPCC, 2007, AR4 WG1)
1961-2003 1993-2003
Thermal 38% 58%
Expansion
Glaciers 45% 28%
Greenland 4% 7%
Antarctica 13% 7%
Total 1.8mm/year 3.1 mm/year

7. IPCC 2007 statement
• Climate has changed on all time scales throughout Earth’s history.
• The concentration of Carbon dioxide in the atmosphere has reached
a record high relative to more than the past half-million years, and
has done so at an exceptionally fast rate.
• Current global temperatures are warmer than they have ever been
during at least the past five centuries, probably even for more than a
millennium.
• If warming continues unabated, the resulting climate change within
this century would be extremely unusual in geological terms.
• Another unusual aspect of recent climate change is its cause: past
climate changes were natural in origin whereas most of the warming
of the past 50 years is attributable to human activities.

8. Future sea-level rise
• IPCC 2007 predictions
global sea level could be between 18 and 59 cm higher
than 1980-1990 levels by 2100.
• UK Government has done a subsequent analysis
(UKCP09).
They have suggested values of 37 to 53 cm for S.
England are most likely by 2100.

9. Future sea-level rise
• IPCC 2007 predictions
global sea level could be between 18 and 59 cm higher
than 1980-1990 levels by 2100.
• UK Government has done a subsequent analysis
(UKCP09). They have suggested values of 37 to 53 cm
for S. England are most likely by 2100.
• Changes of up to 190 cm are possible by 2100, but
VERY unlikely.

10. ?
Global sea-level rise
(IPCC, 2007, AR4 WG1))

11. Local sea level
• Geological Land Movement
• Tsunami
• River runoff
• Storm surges
• Astronomical tides
• Wind waves and swell

12. Local sea level
• Geological Land Movement
• Tsunami
• River runoff
• Storm surges (part of extreme water levels)
• Astronomical tides (part of extreme water levels)
• Wind waves and swell (not discussed)

13. Geological land movements
1 mm/year sinking

14. Relative Sea-Level Rise
• Measures relative movement of the land
to the sea – absolute ocean change plus
land uplift/subsidence
• Measured with tide gauges – digitising
records every 15 minutes or hour with
quality control rules on missing data
• One annual estimate of mean sea level is
the mean of > 8,000 measurements.

15. Example Tide Gauges
(float gauge)
Source: National Oceanographic Centre

16. Sea level in the English Channel
• A major data archaeology exercise has been conducted.
• Paper-based records:
– St Marys, Isles of Scilly,
– Weymouth, for
– Southampton
– Newhaven
• Correction of previous errors:
– Devonport
– Portsmouth
• Collectively, about 150 years of data have been added to
the English Channel sea-level record.
(I.D. Haigh PhD 2009)

17. Mean (and extreme) sea level
English Channel data extension
Source: Haigh et al, 2009 Continental Shelf Research

18. Mean sea-level (MSL) trends (mm/yr)
for 20th Century
Station Name MSL trend
(mm/yr)
St Mary’s 1.72 ± 0.52
Smallest sea level
Newlyn 1.74 ± 0.06
rise at Southampton
Devonport 2.07 ± 0.63 and Portsmouth
Weymouth 1.81 ± 0.28
Sheerness (Thames
Southampton 1.30 ± 0.18
Estuary) has higher
Portsmouth 1.21 ± 0.27 sea level rise than all
Newhaven 2.27 ± 0.27 Channel Ports
Dover 1.93 ± 0.21
Sheerness 2.43 ± 0.09
Source: Haigh et al, 2009 Continental Shelf Research

19. Sea level in the English Channel
• Mean sea levels and extreme sea levels
have been rising at a similar rate through
the 20th Century.
• The rate of rise is in the range 1.2 to 2.3
mm/yr, with 1.3 mm/yr at Southampton.
• Average value is 1.7mm/year – similar to
global trends during the 20th Century

20. Sea level in the English Channel
• Sea-level rise accumulates and increases the
likelihood of flooding during storms – all things
being equal.
• A water level that on average occurred once
every 100 years in 1900 now occurs on average
every 10 to 25 years.
• As sea levels continue to rise and probably
accelerate, this increase in the likelihood of
flooding will continue.

21. Sea level in the English Channel
Changes at Newlyn (50cm rise in 100 years)
Source: Haigh et al, 2011 Maritime Engineering

22. Flooding in the Solent

23. The Solent Flood Plain

24. Southampton
Annual sea levels:1935 to 2010
6.0
10 March 2008
Annual extreme
5.0 level
Height (m CD)
Trend = 1.2 mm/yr
4.0
3.0
Mean level
Trend = 1.4 mm/yr
2.0
1900 1920 1940 1960 1980 2000 2020

25. 10 March 2008
Source: Haigh et al., 2011, Maritime Engineering

26. 10 March 2008
Source: Haigh et al., 2011, Maritime Engineering

27. Southampton
10 March 2008, high tide

28. Sandbanks, Dorset
10 March 2008, high tide

29. Yarmouth
10 March 2008, high tide

30. Yarmouth
10 March 2008, high tide

31. Yarmouth
10 March 2008, high tide

32. Emsworth
10 March 2008, high tide

33. Historic flood analysis
• What is the relationship between high sea
levels at Southampton and Portsmouth
and coastal floods? (1935 to 2005 and
1961 to 2005, respectively)
• What sites in the Solent that have been
particularly flood-prone?
• Are there significant changes in the
occurrence of coastal flooding in recent
decades?

34. Methods (1)
• Identify the 100 highest sea levels at Southampton and
Portsmouth
• Define events that lead to flooding using the newspaper
records (The Echo and the News)
Event Type Description
Category
1 Definite coastal flood event around high tide.
2 Possible flood event, but coastal influence uncertain.
3 Extreme weather event recorded, but no flood
occurrence recorded.
4 No acknowledgment of weather or flood event.
Source: Ruocco et al., 2011, Natural Hazards

35. Methods (2)
• For Category 1 events (certain coastal floods), the severity
is defined
Severity level Description
5 Flooding over larger areas. Significant pumping required by emergency
services. Generally more than half a day disruption to homeowners and
road users. More than 15 properties affected
4 More than 5 properties affected by flooding.
3 More than 3 roads affected and/or at least one property affected.
2 Some road flooding – usually localised or shallow.
1 Flooding in open areas/quay areas – no real structural damage or
disruption.
Source: Ruocco et al., 2011, Natural Hazards

36. Flood events occurrence and severity
Event Type Category Southampton Portsmouth
1 58 53
2 10 11
3 5 2
4 27 34
Source: Ruocco et al., 2011, Natural Hazards

37. Flood Occurrence
´
12
11
10
9
15
13
8 14 23 25
16 20 21 26
7
4 17
6 18 19
5 27
22 24
36 35 34
3
28
1 32
2 37
Number of flood
33
events recorded
28+
31
20-23
30
16-19
13-15
29
10-12
7-9
0 3 6 12 Kilometers 4-6
1-3
Source: Ruocco et al., 2011, Natural Hazards

38. The Top 10 Events
1935 to 2005
Date of Number of Southampton Portsmouth
flood locations Total sea level (m rank Total sea level rank
affected CD) (m CD)
14/12/1989 21 5.34 12 5.21 70
10/01/1993 19 5.48 2 5.36 15
20/12/1983 17 5.34 14 5.43 6
13/12/1981 15 * * 5.42 8
08/12/1954 14 5.38 11 * *
23/11/1984 14 5.29 20 5.48 3
17/12/1989 14 5.25 33 5.21 71
07/12/1994 12 5.46 3 5.5 1
24/10/1961 11 5.41 7 5.41 9
07/10/1987 10 5.24 34 * *
* No sea level data is available for these events; hence the rank cannot be determined.
Source: Ruocco et al., 2011, Natural Hazards

39. 14/17 December 1989 Flood
Fareham
´
Emsworth
Lymington Portsmouth
Severity of
flood
5
4
3
2
0 5 10 20 Kilometers
Source: Ruocco et al., 2011, Natural Hazards

40. Cowes
14 December 1989 Flood

41. Extreme sea levels and coastal
flooding
Southampton Portsmouth
Southampton Portsmouth
Source: Ruocco et al., 2011, Natural Hazards

42. Flood Modelling

43. Flood Analysis -- Methods
Source: Matt Wadey

44. Yarmouth 2008 Flood
Source: Matt Wadey

45. Yarmouth Future Flood
2008 Flood plus 0.5 m SLR
Source: Matt Wadey

46. Yarmouth Future Flood
2008 Flood plus 0.5 m SLR
Source: Matt Wadey

47. Yarmouth Future Flood
2008 Flood plus 0.5 m SLR
Source: Matt Wadey

48. Regional Flood Analysis
Buildings flooded to 1-m depth across the Solent
in a single tidal cycle
0.5 m rise 1.0 m rise
Source: Matt Wadey

49. Planned Adaptation to SLR
Source: Nicholls (2010) Book on “Understanding Sea-Level Rise and Variability”

50. Other Adaptation Response
Options
• Forced/Unplanned retreat
• Attack (build seaward)

51. Made Land Southampton
Source: West, 2011. Solent Estuaries - Introduction: Geological Field Guide. Internet site:
www.soton.ac.uk/~imw/Solent-Introduction.htm. Version: 3rd June 2011

52. Concluding remarks
• Sea levels are rising globally and in the
English Channel, including the Solent.
• This will continue and likely accelerate.
• This is raising extreme events and
threatens more coastal flooding in the
future unless we respond.
• Many adaptation options are available –
especially if we plan now.

53. Acknowledgements
• Dr. Neil Wells, University of Southampton,
National Oceanographic Centre
• Dr. Ivan Haigh, University of
Southampton, National Oceanographic
Centre
• Amy Ruocco, former MSc Environmental
Science student (currently URS,
Basingstoke)
• Matt Wadey, PhD student

54. Questions?

55. Flooding and sea-level rise
in the Solent Region
Robert J. Nicholls
Faculty of Engineering and the Environment
University of Southampton
r.j.nicholls@soton.ac.uk
South Coast green breakfast series