CLIMATE CHANGE ON THE SEVERN ESTUARY Coastal Risk in the Bristol Channel – a Meteorological Survey On the Bristol Channel storms and storm surges have occurred throughout history, and have been the cause of substantial damage and flooding from the sea both in the past and more recently. These include events of the Little Ice Age, particularly severe damage in 1607 and between 1690 and 1720 (Lamb and Fryendahl 1991, Horsburgh and Horritt 2006). A number of more recent storm and storm surge events are shown in Fig1. During the years 1981, 1984 and 1990 there were significant storm surges which caused South Wales Severe Storms North Somerset Coast and South East Wales substantial damage and flooding along the coast of Somerset and some coastal flooding over Severe storms on the south Wales Severe flooding caused by a storm surge in 1607 has low lying areas of SE Wales, especially the event of 1990. Notable storms also occurred in coast in March 2008 were reported (19) been reported as possibly the worst coastal flooding and the media also reported damage ever recorded for the Bristol Channel and Severn Estuary 1996, 2008 and 2010, all of which caused damage along exposed coastlines of Somerset and along the Somerset coast during the area(16). some limited coastal damage and flooding in south Wales. same period. Tewkesbury e c i v Forest r A good knowledge and understanding of the causes of such storms and surges is very helpful e s of d e Gloucester i in assessing the associated risks that these events might present, both now and in the future. l p Dean p u Monmouthshire s It can also inform the planning process. G l o u c e s t e r s h i r e W A L E S A N I Stroud D E / y e v r u S e KEY FINDINGS c Newport n Burnham-on-Sea, Brean and South a Bridgend n d Highbridge Flooding N Gloucestershire r Cardiff O Similarities between 1981 surge and 2008 surge n A Burnham-on-Sea, Brean and Highbridge Bristol . (15) The Vale of Glamorgan 0 30 1 are all located on the Somerset coast Y 0 North 2 Importance of SE'ly winds in creating a bulge in R t north of the River Parrett estuary and are A h Kilometres g U Somerset i E N G L A N D r water which travels up-channel as a significant at risk from extreme tidal flooding events T y S p S E E o (from storm surges and extreme V N C E R surge n weather). The area has a history of w o Sedgemoor r Exmoor C flooding with significant events occurring Strong/gale force winds from the W'ly quadrant National Park © in 1859, 1903, 1910, 1926 and 1981 West Somerset important in causing modest sea surface when considerable damage was caused. Storm Surges There is a flood defence scheme present elevations and overtopping by wave action Somerset storm surges along the coast protecting these areas. S o m e r s e t have recently occurred The Environment Agency admits there in 1981, 1984 and Importance of NE'ly winds in erosion and coastal remains a possibility that extreme severe Somerset Coast Tidal Flooding ( 1 7 ) flood events could overtop or breach the 1990 , flooding risk to those areas exposed, particularly the s On 13th December 1981 a 1.45m tidal surge occurred close to the Chepstow in 1981 and flood defences and flood the areas behind peak of a spring tide along the Somerset coast. Tidal defences Wales coast near Penarth them. If this were to occur, several 1 9 9 0 , w i t h t i d a l breached across long lengths of Somerset's north and west facing thousand properties may be affected. No flooding also taking Importance of short timescale events defence can give absolute protection; it coastline. Sea water flowed back to the M5 motorway, flooding place in 1994, 1997 can only reduce the risk of flooding. communities and hundreds of hectares of open land. and 1999(18). Examples of severe storm and tidal events affecting the Severn Estuary, adapted from Hovey et al. 2010. High water events This timeline shows the maximum elevation of water at the tide gauge at Avonmouth referenced to Ordinance Datum Newlyn put in date order. The bars indicated in Dark Blue are purely tide with little or no weather impact. The bars indicated in Red are events which have known to have caused coastal damage or overtopping. Data from BODC. 9 Level of 1981 storm surge event e g 8 a M u Mean High Water Springs level n 7 g i t Damage caused x 6 h a Weather related 5 Non-weather related M 0 Year 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 CLIMATE CHANGE ON THE SEVERN ESTUARY Storm Surge References Storm surges are an elevation of the sea surface above Phillips M R 2008. Consequences of short term changes in coastal normal predicted astronomical tide levels and are caused by processes: a case study. Earth Surface Processes and Landforms a combination of low atmospheric pressure and wind stress 33, 2094-2107 (2008) on the sea surface. They are particularly damaging when Proctor R and Flather R A 1989. Storm surge prediction in the they occur at or near high water (Horsbourgh and Horrit Bristol Channel – the floods of 13 December 1981. Continental 2006). Under certain meteorological conditions the surge Shelf Research, 9(10): 889-918. Pressure can be very large and can cause extensive damage and tidal Hovey C E and Rodgers N P 2010. IMCORE Climate Change Report Sea flooding particularly to exposed areas of Somerset and Cards surface www.severnestuary.net/sep/partnership/.../ClimateChanegReportC L O W P R E S S U R E parts of s Wales as happened in 1981 (Proctor and Flather 1989) ard2.pdf, accessed 3 May 2011. Horsburgh K and Horrit M 2006. The Bristol Channel floods of 1607 – reconstruction and analysis. Weather 61(10): 272-277. S S W I N D S T R E Lamb HH with Fryendahl K 1991. Historic storms of the North Sea, British Isles and Northwest Europe. Cambridge. Cambridge SURGE Property Sea University Press. Defence Lewis, MJ, Horsburgh, K, Bates, PD & Smith, RAE. 'Journal of TIDE Coastal Research', Quantifying the uncertainty in future coastal flood risk estimates for the UK, 27, (pp. 870-881), 2011. ISSN: Source: adapted from:Lewis, MJ, Horsburgh, K, Bates, PD & Smith, RAE. 'Journal of Coastal Research', 2011. 1551-5036 10.2112/JCOASTRES-D-10-00147.1 BODC.ac.uk – accessed 21June 2011 The wind threat All charts adapted from UK Met Office originals available at:(www.wetterzentrale.de/topkarten/tkfaxbraar.htm) Three broad weather patterns have been identified which lead to coastal erosion/flooding and overtopping of sea defences. In addition to storm surges, the impact of more localised winds is also important to coastal risk on the estuary. An Surface synoptic chart for: Surface synoptic chart for: Surface synoptic chart for: example of this is the impact of north-easterly winds on the 0000UTC 31 March 2010 0000UTC 10 March 2008 0000UTC 10 Jan 2010 coastline near Penarth Head in Wales. When the wind is from the north-east, this section of coastline is exposed to a large HIGH fetch in the same direction and significant coastal erosion has occurred (Phillips 2008). In addition, winds from the south- east cause erosion to the western side of Whitmore Bay, Barry. LOW LOW Contacts and further information Produced by N. Rodgers, Cardiff University Marine and Coastal Environment Research Group (MACE), as part of the IMCORE project (Innovative Management for Europe’s Changing Coastal Resource). For more information please visit: www.imcore.eu Or contact: School of Earth & Ocean Sciences, Cardiff University, Westerly flow resulting in strong or gale Deep areas of low pressure or troughs, Strong E or NE'ly winds which can cause force winds from the westerly quadrant. which transit the channel such that strong damage to exposed coastlines, especially in Long westerly fetch, shear stress on water or gale force SE'ly winds are experienced s Wales. Fetch to the NE of Penarth head is causes elevations in sea surface. ahead of the trough with gale force W'ly locally the greatest for that stretch of winds behind it, similar to 1981 event. coastline..