Jncc coastal Directories Project Region 11 The Western Approaches

2.5.1  Sea-level changes in the region
Apparent sea-level rise is the combined effect of local crustal
movements (owing to the removal of the weight of ice since
the last glacial period, Scotland is rising whereas south-
eastern England is sinking) and global rises in sea level,
estimated as rising between 1.5 and 2 mm/year (Woodworth
1987).  Reviews which attempt to estimate future changes in
apparent sea level (e.g. Woodworth 1987) cite the regional
and temporal variability shown by tide gauge data as major
causes of uncertainty.  In this region, sea level trends
between 1917 and 1981, measured on a tide gauge at
Newlyn, show an average annual rise in relative sea level of
0-3 mm/year (
Map 2.5.1
) (Emery & Aubrey 1985).  This
value includes both the global rise and the uplift in the land
level, the rate of which is calculated to be 0.7 mm/year.   
Holocene sea-level changes in south-west England and
Wales, inferred from radiocarbon dates of peat deposits,
have been summarised by Heyworth & Kidson (1982).  Such
peats are exposed in the intertidal zone in Mount’s Bay,
Barnstaple Bay (Westward Ho!) and Bridgwater Bay, as well
as at depth within the Somerset Levels.  Results suggest that
sea level has risen steadily by 5 m over the last 5,000 years.
The results from the English Channel, Bristol Channel and
Somerset Levels were in general agreement, confirming that
there has been little vertical movement of these areas
relative to each other.
2.5.2  Flooding risk
There are extensive areas of low-lying land in the region that
are susceptible to flooding.  The main areas at risk are within
the Severn Estuary and along the coast of Bridgwater Bay
(
Map 2.5.1
).  Parts of the coast at Mount’s Bay, Portreath,
Perranporth, Porlock and south of Porthcawl are susceptible
to local flooding.  Long stretches of the coast of the Somerset
Levels and the shores of the Severn Estuary are protected
from flooding by man-made defences (see also 
section 8.4
).
2.5.3  Further sources of information
A.  References cited
Emery, K.O., & Aubrey, D.G.  1985.  Sea levels, land levels, and tide
gauges.  New York, Springer-Verlag.
Heyworth, A., & Kidson, C.  1982.  Sea-level changes in south-west
England and Wales.  Proceedings of the Geological Association, 93:
91-111.
Woodworth, P.L.  1987.  Trends in UK mean sea level.  Marine
Geodesy, 11: 57-58.
B.  Further reading
Anon.  1992.  The Irish Sea Forum: global warming and climatic change -
seminar report.  Liverpool, University of Liverpool Press.
Boorman, L.A., Goss-Custard, J.D., & McGrorty, S.  1989.  Climatic
change, rising sea level and the British coast.  London,
HMSO/Natural Environment Research Council.  (Institute of
Terrestrial Ecology Research Publication No. 1.) 
Burd, F., & Doody, P.  1990.  Sea level rise and nature conservation.  A
review of NCC experience.  Peterborough, Nature Conservancy
Council.  (Coastal Ecology Branch, Coastal Habitat Network
Paper No. 3.)
Climate Change Impacts Review Group.  1991.  The potential effects of
climate change in the United Kingdom.  Report 1.  London, HMSO.
(Department of the Environment.)
Department of the Environment.  1988.  Possible impacts of climate
change on the natural environment in the United Kingdom.  London,
HMSO.
Department of the Environment.  1992.  The UK environment: coast
erosion, flooding and sea level change.  London, HMSO.
Department of the Environment/Meteorological Office.  1990.
Global climate change.  London, HMSO.
Doornkamp, J.C., ed.  1990.  The greenhouse effect and rising sea levels
in the UK.  Nottingham, M1 Press.
Motyka, J.M., & Brampton, A.H.  1993.  Coastal management: mapping
of littoral cells.  Oxford, HR Wallingford.  (Report SR 328.) 
Posford Duvivier Environment.  1991.  Environmental opportunities in
low lying coastal areas under a scenario of climate change.
Peterborough, Report to National Rivers Authority, Department
of Environment, Nature Conservancy Council and Countryside
Commission.
Rendel Geotechnics.  1995.  Coastal planning and management: a
review of earth science information needs.  London, HMSO.
Shennan, I.  1989.  Holocene crustal movements and sea-level
changes in Great Britain.  Journal of Quaternary Science, 4: 77-89.
Shennan, I.  1993.  Sea-level changes and the threat of coastal
inundation.  The Geographical Journal, 159(2): 148-156.
Shennan, I., & Woodworth, P.L.  1992.  A comparison of late
Holocene and twentieth-century sea-level trends from the UK
and North Sea region.  Geophysical Journal International, 
109: 96-105. 
Tooley, M.J., & Shennan, I., eds.  1987.  Sea level changes. Oxford,
Basil Blackwell.  (Institute of British Geographers Special
Publication Series, No. 20.)
Woodworth, P.  1990.  Measuring and predicting long term sea level
changes.  NERC News, 15: 22-25.  Swindon, NERC.
Region 11  Chapter 2  Geology and physical environment
34
2.5  Sea-level rise and flooding
British Geological Survey
Region 10
Region 12
5°W
Land below 5 m potentially
susceptible to flooding
Porthcawl
Bridgwater Bay
Somerset Levels
Porlock
Barnstaple Bay
Perranporth
Portreath
Newlyn
Mount’s Bay
Recent relative sea-level rise
in mm/year
0
+2
+4
Map 2.5.1
Estimated rates of recent relative sea-level rise (mm/yr),
low-lying areas susceptible to flooding and locations
mentioned in the text.  Source: after Emery & Aubrey
(1985).

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