Page 1 of 15 - Shetland Islands Council · coastal geomorphology, notably on the impacts of...

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This document contains the summary of the presentations made to Shetland Islands Council at the Transport and Environment Forum held in the North Atlantic Fisheries College on 1st March 2005 by Dr James Hansom, Dr Adrian Hall and Professor David Smith. Also included in this document are the notes from the meeting.

Dr James Hansom is from Glasgow University. He works in the field of coastal geomorphology, notably on the impacts of changing coastal environments. He has experience working in high latitude coastal areas of both northern and southern hemispheres, where storminess is an important component in coastal change.

Dr Adrian Hall is from Fettes College Edinburgh, and St Andrews University. He has published widely on Quaternary history in Scotland, especially on the patterns of the last glaciation, and has published on the effects of storms on the Shetland coastline, notably on the power and effectiveness of storm waves.

Professor David Smith is from Oxford University. He worked on sea level change in many areas of Scotland including the mainland, Inner and Outer Hebrides and the Northern Isles, including Shetland. His particular interests lie in the effects of glacio-isostasy on the one hand and tsunami on the other. He first identified evidence for the Storegga tsunami on Shetland and has since worked on tsunami in several areas of the world. He has led several EU projects examining sea levels and storminess in Scotland, including Shetland.

For additional information the slides from the 3 presentations form an appendix to this document.

N.B the photomontage that is the cover for this document is for illustrative purposes only – it is not meant to be an accurate prediction of what may occur in the future.

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Climate Change and Coastal Hazards on Shetland

Summary of Presentations to Shetland Islands Council

Scalloway Monday 28th February 2005

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Context of coastal change on Shetland Dr James Hansom

Shetland benefits from a hard rock coastline which slows the impact of coastal processes and thus on any changes that are forced. However, in terms of the drivers of coastal change, Shetland suffers the disadvantage of a slowly rising sea level, a severe wave energy environment whose maximum wave heights have been increasing over the last few decades and, as a function of its rocky and indented nature, an extremely limited supply of coastal sediment available to come onshore to produce beaches. Thus the soft coastal features of Shetland, are regionally rare and are a valuable resource both in terms of recreation and as the site of a significant number of key elements of infrastructure.

The net result of interaction of these conditions render the coast of Shetland subject to change over a range of timescales. Rock coasts are changing on a timescale that does not interact in a significant way with infrastructure or agriculture, but beaches are changing on a much faster and more immediate timescale. This is a problem because many beaches in Shetland carry roads, protect scarce agricultural land, and support or protect major infrastructure (eg Sumburgh airport, various ferry terminals and installations). The recent trend of coastal flooding and erosion of many of these beaches is of concern not only at present, but also in the future, when enhanced sea levels and wave impacts are predicted and sediment supplies will have dwindled further. Since sediment supply is of equal significance to storminess and sea level rise as a driver of erosion and flooding, any actions that impact negatively on the sediment supply to beaches and reduce the sediment residence time on beaches are to be avoided. For example, armouring of the rear of gravel and sand beaches as a method of erosion control acts to further increase sediment losses via wave reflection and drawdown and may be but a temporary solution that does not fully address the underlying problem.

In many locations beach nourishment may be a more sustainable and more cost-effective solution to beach erosion than armouring and, in the Shetland context, a solution that is appropriate to the bay-head beaches common in the islands. Strategies that conserve sediment, minimise structural intervention, release coastal land to allow flexibility in the position of the coast and that then integrate into a coastal zone management plan are logical ways forward for planning for coastal change in Shetland. This route requires the assembly of a range of data specific to the Shetland coast in order to assess the coastal threat and to assess the risk to beaches, land and infrastructure. Some of this data is available but requires to be assembled in a coherent and targeted fashion. Other data remains to be gathered and this requires a phase of research to progress in parallel with the task of data assembly from existing sources.

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Assessing the Storm Hazard Dr Adrian Hall

The record of storm hazards

The Shetland Islands lie along the storm tracks of mid-latitude depressions . Intense depressions generate high winds and agitated sea states, resulting in hazards that include wind damage, extreme waves, inundation, ship wreck and coastal erosion. The extremes of wind, with maximum recorded gusts in excess of 150 mph, mean that the storm hazard on Shetland is perhaps greater than anywhere else in the British Isles.

At least six major storms are recognised in the 20th century in which wind speeds exceeded 60 knots. Each storm occurred in the winter months of December through to February. Each caused the impact of large waves at the coast, with associated erosion and local inundation. Documentary evidence of earlier storms is less reliable but major storms are identified in 1634, 1669, 1792 and 1862. An unexplored archive of information about past storms is provided by sediments in bogs close to current sea level and by boulder deposits on cliffs on the exposed outer coast of Shetland. Preliminary dating of sands from boulder deposits at Villians of Hamnavoe indicates that at least one major storm occurred in the early 17th century.

An association exists between the highest wind speed in gusts recorded at Lerwick and reports of damage from storms. Observations after the 1992 and 1993 storms indicate also that wave water reached higher on cliffs in these storms than in any more recent storm up to February 2005. The storm hazard therefore is generated by the most intense storms, although local impacts can be severe from events of lower magnitude where an unfortunate coincidence between tide, wind direction and coastal configuration funnels water to create surges at the heads of voes.

Intense storms are generated at the Polar Front. Strom intensity reflects in part the pressure gradient between the Icelandic Low and the Azores High. The most intense storms deepen rapidly, within 12 hours, and the storm system may also be fast moving. The time window for forecast and warning is correspondingly small. The cyclone centre may be no more than 50 km across and impacts along the 120 km N-S length of the Shetland Islands can therefore vary greatly. The maximum winds and associated wave heights occur in the SE quadrant of the depression system. Maximum impact can be predicted where this zone crosses the coast.

The track of the storm determines the locus of impact on Shetland. The 1992 and 1993 storms tracked NE, causing maximum damage on North Mainland and Unst. The 1953 storm tracked SE, with damage concentrated in South Mainland. As the storms cross Shetland the wind may swing to the SE, giving high seas on coasts including Out Skerries and Mousa and may be accompanied by tidal storm sure in Lerwick. This pattern appears to have

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been followed by the 1900 storms which inundated Clickhimmin and led to widespread damage up to 5 m OD around the harbour at Lerwick.

Storm hazards in the future: possible impacts of climate change

Estimated sea level rise on Shetland over the next century is around 1 m. Any future change in storminess will be superimposed on this, extending inland the limit of storm driven wave water. The period since 1955-1994 saw a steady rise in storm intensity and an associated increase in average and extreme wave heights in the North Atlantic (WASA). Most models indicate further increases in storminess as a result of any increase in mean annual air temperatures in the NE Atlantic.

In the 21st century storm intensity is predicted to increase, with the focus of intensity migrating eastwards across the Atlantic, so becoming greater in the Shetland-Norway area.

The latest STOWASUS models indicate significant local and seasonal variation in sea states in the eastern North Atlantic. An increase in significant wave heights is predicted in Norwegian waters in winter but at 60° N in North Sea there may be little apparent change even for the largest waves with a 100-year recurrence interval.

Sea level change and tsunami Professor David Smith

Sea level change In most parts of the world, coastal flooding from the sea is the product of rapid and high magnitude events superimposed upon long-term, or secular, changes. In the British Isles, the high magnitude events may be storm surges or tsunami. The secular events are one the one hand land movements caused by isostatic changes following the last glaciation, and on the other, sea surface movements caused by climate change, the combination of land and sea surface changes resulting in an apparent, or relative change in sea level at the coast.

Since the Fourth Biennial Flood Report was produced, we have learnt more about both coastal flood events and secular sea level changes in Shetland, and although our knowledge is still generalised, we are closer to understanding the threats posed to economy and society in Shetland.

The only study to have outlined changes in the level of the sea surface offshore NW Europe since the last glaciation was that of Morner. He based his graph on a projection of shoreline altitudes in Scandinavia. The main features of the graph are the fluctuations evident and the rapid rise in the sea surface up to about 6000 radiocarbon years BP. In Shetland, secular sea level changes will have included a component of land movement due to the effect of ice loading and subsequent unloading. At the maximum of the last glaciation, Shetland was covered by an ice sheet which recent information

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indicates probably extended westward to the edge of the continental shelf in the Faroe-Shetland channel. This will undoubtedly have resulted in isostatic effects, as may the nearby Scandinavian ice sheet. There would have been crustal uplift in the area as and after the ice melted, but this uplift would have varied according to the original thickness of the ice, thus greater over Mainland than over the outlying islands. Taking account of this, even with the complications of both the proximity of the Scandinavian ice sheet and water loading on the continental shelf as the ice retreated, it is highly likely that crustal movements varied across Shetland, so that rates and patterns of relative sea level change in the past will have varied according to location.

Future sea surface changes around Shetland are likely to reflect global climate change. In the IPCC Third Assessment, a range of scenarios is given, estimating global average sea level rise of between 9 and 88cm from 1990 to 2100. The best estimate figure was 49cm. It should be recognised that this relates to generalised global changes: in different areas of the world, including Shetland, the actual changes will be different. In addition, if the land is sinking – and this has not been proven – the relative change will be greater. Recent research is suggesting that the rate of rise in global average sea surface levels will increase after about 2040, and in this context the estimate given in the Fourth Biennial Flood Report of up to 50cm over the 2004 level by 2100 could be on the conservative side. Further, it should be noted that modelling recently undertaken indicates that as sea level rises, the tidal range in estuaries will be greater than the rise by up to 25%. Overall therefore, whatever sea level rise scenario is proposed, the consequences for Shetland’s indented coastline with its long firths should not be underestimated, despite the uncertainties.

TsunamiUntil relatively recently, tsunami were unheard of in Shetland. However, discovery of the Holocene Storegga Slide tsunami in 1988 changed everything and since that time tsunami activity around Shetland’s coasts has been actively considered. Since the Fourth Biennial Flood Report, detailed studies of the anatomy of the Storegga tsunami by groups from Norway and the United Kingdom have provided detailed evidence of the event. It is now recognised to have taken place in the autumn of a year around 8000 BP; inundated the heads of firths up to a minimum of 25m above the High Water Mark of the time (an inundation higher than anywhere else in the United Kingdom); and refracted around islands, sometimes reaching higher levels on coasts in the lee of the approaching waves. In Shetland, evidence for this event is widely displayed along peat cliffs and low-lying valleys, demonstrating that tsunami can reach into many areas even of a crenulated coastline and strike with considerable force. The greatest force of the tsunami was probably experienced on exposed headlands, but the greatest inundation was in inlets, where today coastal populations are concentrated.

It has sometimes been suggested that the Storegga event was a one-off, unlikely to happen again. However, recent studies are beginning to indicate that tsunami may have been more frequent visitors to the shores of Shetland

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and for that matter the coastlines of NW Europe as a whole. Since the mid 1970s, an increasing number of seismic surveys of the continental margins of the N Atlantic, and especially around NW Europe, have been undertaken. They have disclosed a large number of submarine slides like Storegga. Although dates for these events as yet are few, the slides appear to have been developed in glacial sediments, and the form of the slides shows that, whilst many occurred shortly after the ice sheets melted, many have also occurred in more recent times. Along the continental margin north and south of Shetland there are a number of slides, including along the Faroe-Shetland channel, where detailed studies undertaken by the British Geological Survey have disclosed repeated re-mobilisation of the slide sediments. Although the generation of a tsunami by submarine slides depends upon a number of coincidences, including a sufficiently rapid movement and of course a sufficiently large amount of sediment, these circumstances can occur. In addition, the slide does not have to be as large as the Holocene Storegga Slide. In 1946, the Unamak slide offshore southern Alaska, which covered an area on the sea bed of about 1200 km 2, less than a twentieth that of the Storegga event, generated waves 35m high – higher than those yet suggested for Storegga. Along Shetland’s coasts there are several locations where sand horizons similar to those deposited during the Storegga event, occur, notably at Basta Voe, on Yell, indicating that tsunami, possibly generated by the movement of one of these slides, may well have occurred more recently than the Holocene Storegga Slide tsunami..

Whilst we should not over-emphasise the tsunami threat, it is worth remembering that even relatively small tsunami waves are far more likely to inundate coastal areas than storm waves because they involve landwards translation of the whole water column, rather than the surface of the water. Plainly, their effect will be exacerbated if they strike at high tide.

SummaryMany uncertainties surround estimates of both future sea level rise and tsunami. However, it can be said with some confidence that sea level rise is occurring and that the Holocene Storegga Slide tsunami was probably not the only tsunami to have reached Shetland. Planning needs to take account of the impact of both phenomena. In the short term, less than a generation, planners may wish to consider the effects of sea level rise on groundwater effects and the loss of small areas of agricultural land, together with the effects on ferry piers, archaeological sites and perhaps aquaculture. In the medium and long term, serious consideration should be given to the siting of proposed buildings of great community and commercial value, together with the communications infrastructure. It is probably true that Shetland’s coasts are more likely to experience inundation and erosion due to sea level rise, storms and tsunami impact than any other areas of Scotland.

Recommendations

Assessment of sites at risk from coastal change is required via: search for all vulnerable sites below 5m OD; determine current status of sites in terms of erosion (not the same as flooding alone); determine past

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coastal erosion, sediment budget and flooding record of key beach sites using time series aerial photography, documentary records, ground photography, maps and marine charts.

Assessment required of status and sustainability of current shore protection methods and to investigate feasibility of alternatives.

Assessment required of current and future changes in the wave environment of Shetland and the impact and chronology of storminess.

Assessment required of impact of sea level rise and high energy events (eg. tsunami) on the Shetland coast.

Integrate recommendations for flood and erosion planning within Shetland Shoreline Management Plan and in due course to mesh this with the much more encompassing aims of a Shetland Coastal Zone Management Plan

Several of the above points require further research to establish key missing elements (eg. storm frequency, storm chronology etc). This research needs to be tightly targeted on Shetland issues.

Strategic meeting needed with Infrastructure and Planning to identify key requirements, agree programme of data gathering and research, and identify funding needs.

Dr Adrian M Hall1Dr James D Hansom2

Professor David E Smith3

1 Fettes College, Carrington Road, Edinburgh EH4 1QX 2 H3 F

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ShetlandIslands Council

NOTE Environment & Transport Forum North Atlantic Fisheries College, Scalloway Tuesday 1 March 2005 at 10.30 a.m.

Councillors:J A Inkster I Hawkins J H Henry Capt G G Mitchell W Tait

In Attendance (Officers):A Hamilton, Head of Planning V Hawthorne, Development Plans Manager A Cogle, Service Manager – Administration

ApologiesD Cameron, SEPA N Flaws, HIAL J Holmes, Scottish Executive S Kerr, SIC A Jamieson, SIC L Kerry, SIC I Napier, NAFC R Nickerson, SIC D Okill, SEPA E Perring, SIC D Sandison, SSFA J Simpson S Thomson, Fair Isle Committee P Wishart, SIC A Wishart, LPA

Invited to Attend:F B Grains J C Irvine F A Robertson

J Astwood, SIC B Barron, SIC L Gray, SIC G Hughes, SIC J Jamieson, SIC D Lamb, SIC

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G Leask, SIC I McDiarmid, SIC S Pearson, SIC T Saunders, SIC A Taylor, SIC T Smith, SIC S Shearer, SIC D Williamson, SIC

P Burgess, Shetland Islands Tourism N Davies, Living Shetland P Ellis, RSPB W Fraser, ASSCK Hall, SNH P Harvey, Shetland Amenity Trust M Holmes, NAFC M Hume, Scottish Water A Leask, Crofters Foundation A Longmuir, Seabirds and Seals J McEvoy, NAFC N Martin, Shetland Heat Energy & Power D Watson, Shetland Enterprise A Sandison, Arch Henderson J Swale, SNH

Chairperson:Mr J A Inkster, Chairperson of the Forum, presided.

Mr A Inkster welcomed everyone to the meeting, saying that it was good and very encouraging to see such a good turnout. He went on to say that the Environment and Transport Forum today was to specifically consider environmental issues. Mr Inkster said that the Council had a number of Forums, which were formed to provide a mechanism for discussion and debate which would assist and influence the formulation of Council policy.

CircularThe circular calling the meeting was held as read.

3/05 Community Planning Board Update – ChairpersonMr Inkster said that as Chairperson of the Forum, it was his responsibility as a Member of the Community Planning Board to report back to the Forum with regard to the outcome of recent meetings of the Board. He advised that the Community Planning Board joined up local agencies with regard to the provision of various services throughout Shetland. Mr Inkster said that the last meeting of the Board had been an informal one, and had involved discussion with representatives of Highlands and Islands Enterprise. He said that whilst there were disagreements between

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the Council and Highlands and Islands Enterprise regarding the funding of the extension of the runway at Sumburgh Airport, discussion on this matter had been constructive, and there was no further detail to report at this time.

4/05 Climate Change Impacts on Shetland The Forum noted the discussion paper presented by the Head of Planning (Appendix 1) and Mr Inkster provided a short introduction to the speakers, giving details of their background and the presentations to be given today, and handed over to Mr Adrian Hall to begin the presentations.

Mr Hall began by giving some additional background information regarding the work carried out by each of the speakers. Mr Hall advised that each of the speakers would be happy to take questions at the end of each presentation, and the presentationswould conclude with a short summary and opportunity for further questions to all three speakers.

Dr Jim Hansom – Shetland Coast: The Context of the Coastal Change

Dr Hansom provided a detailed presentation regarding the geology of Shetland’s coastline, and the effect of the wave energy and storm impact on the coastline, and observations and predictions regarding coastal erosion. A copy of the presentation slides is attached as Appendix 2.

In response to a question regarding the process for re-instating beaches, Dr Hansom said if the amount of sediment which was being lost on an annual basis was calculated, the loss over a period of 100/150 years could then be calculated. On that basis, a decision could be made as to how often beach feeding should be done, but then other matters had to be considered as to where sand/gravel would come from, and in general whether the beach was of value to the community or infrastructure to spend money on replenishing it. In response to further queries, he went on to say that whilst such projects were expensive initially, these were outweighed by the long term savings, particularly if the beach carried infrastructure, as it was more beneficial than repairing or maintaining with rock armouring. He went on to acknowledge that, particularly in Shetland, traditional methods of living off the land and clearing seaweed from beaches for various uses, may have caused some loss of sediment, as there was some evidence to say that anything that accumulates on beaches would help its stability.

Dr Hansom went on to respond to further questions, in particular commenting on the lack of environmental engineering in the past,

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and the problems that coastal structures were now facing. He explained in detail the methods being used in Holland to put beaches back in behind dykes, as it was realised that the beaches were better absorbers of wave energy than the dykes. In this regard, Dr Hansom said that when there was an option of new build or repairing an eroding road, the beach should be put back or the road re-routed.

Regarding the particular effect of oil on beaches, Dr Hansom said that anything that removed sediment was always going to be detrimental, but the decision to remove oiled sand would be dependent upon whether the beach was valuable locally to the community. He said that some consideration could be given to separating the oil from the sand, but agreed that this was a difficult matter, and one that would need careful consideration.

Dr Hansom concluded by saying that the fundamental problem in Shetland was that the sediment supply was limited, and consideration had to be given to encouraging sediment to move onshore. He said due to the rising shore, the best alternative would be to take sand from elsewhere, but the source would always be difficult. He said that gravels could be used and were easily sourced from quarries. Dr Hansom said that whilst he did not believe that Shetland was in the realms of artificial reefs, he referred in particular to the Churchill Barriers, some of which were successful and some of which were not.

Professor David Smith – Sea Level Change and TsunamiProfessor Smith gave a detailed presentation regarding the historical, current and future analysis of sea changes around Shetland and Scotland, and provided information on the affects of Storega Slides on the sea levels and highlighted the importance of further research analysis. A copy of the presentation slides is attached as Appendix 3.

Reference was made to information about rising sea levels and various natural phenomena, but it was asked how much of this was attributable to the natural environment, and how much was caused by humans. Professor Smith said that it was undoubtedly true that the climate changes and levels of coastal destruction were nothing compared to what they were years ago. However, there were general changes which could be separated from human evidence of intervention, and were inevitable.

Professor Smith went on to explain that when a slide occurred, there was massive disturbance, but it did not mean that an earthquake had caused the slide. In such cases it was difficult to determine whether any significant sea level changes and resulting flooding were as a result of slides or earthquakes, and this was due to the limited amount of data available. He confirmed that,

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depending upon the size of slide, the size of the initial wave, and so on, at least an hour’s warning could be given on anticipated flooding or tsunami.

Adrian Hall – Storm Hazards: A Shetland PerspectiveDr Adrian Hall gave a detailed presentation regarding the significance and impacts of storm tracks, and information relating to the prediction of future climates and their impacts, and also difficulties associated with the absence of climate and impact information on making those future predictions. A copy of the presentation slides is attached as Appendix 4.

Regarding Lerwick, with a large proportion of infrastructure at sea level which was obviously at some risk, it was asked if there was any strategy that could be started now in order to look towards the future. Dr Hall said that, from a planning point of view, it was clearly a question of design, and that may have to consider whether to some extent buildings were dispensable, although some houses had withstood for several centuries, and been able to withstand the elements. He said that it really came down to the cost and benefit.

Dr J Hansom advised of work being carried out in Venice, where they were raising the heights by 1m and, at same time, sub-tidal masonry work was being carried out below the water. He said that eroding infrastructure required strategies to protect buildings, but also needed to plan for the infrastructure underwater.

Dr A Hall said that there were methods of hard intervention against wave damage, such as reefs, but these simply dampened wave activity and did not remove the effects of storm surges.

Dr A Hall agreed that it was clear from today that what was required was a range of actions toward preventing inundation or erosion. However, choosing the right measure depended on the site in question. He went on to say that what was also had to be learned from today was the dearth of knowledge about the impact of climate and sea level changes on Shetland, and the need for more targeted vision. He said that whilst the Council could commission reports about what will happen in the future when sea level rises, but to some extent work needed to be done now on what the effects had been so far, and whilst problems with sea level rises were common throughout Scotland and elsewhere, they were probably worse in Shetland than anywhere else in Scotland.

Mr A Inkster concluded by saying that the Forum had today been presented with three excellent papers which were well presented and made very interesting by the three speakers. He said that everyone present was now better informed than before, and was very interesting and thought provoking. Mr Inkster said it was

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clear that more research was needed in order to understand the extent to which the impacts being discussed today were being faced.

Mr Inkster thanked the speakers and everyone for attending, and the meeting concluded at 12.40 p.m.

.............................................................................A Inkster CHAIRPERSON

Shetland Coast: the context of coastal change

Jim Hansom

• Shetland sits at the extreme end of the UK geological gradient from a soft and young south-east to a hard and old northwest: an advantage in terms of the protection offered by a hard and resistant rocky coast.

• Shetland’s hard, rocky coast and deepwater nearshore context does not provide much sediment supply to beaches : a disadvantage in terms of the protection of the soft coast.

• Shetland sits at the extreme end of an isostatic gradient centred on an uplifting mainland Scotland and, mainly, subsidence elsewhere: a disadvantage in terms of the impact of sea level rise.

• Shetland sits at the northeastern end of a North Atlantic westerly wave environment that increases in severity towards thenorth and east: a disadvantage in terms of storm impact on both hard and soft coast.

Drivers of coastal erosion

Enhanced wave energy

Reduced sediment supply

Sea level rise

Human intervention

Natural drivers of coastal erosion :

Wave energy• Hs=15m, 1.51 Hs waves

(20m) exceeded 100a –1

(BP Ex, 1995).• Hmax a –1=24.3m W of

Shetland.• 15% increase in winter

wave heights, 1985-95.• 2.5-7.5mma-1 increase in

extreme heights, 1955-94 (Gunther et al., 1998).

% increase in N Atlantic winter wave heights 1985-95

• 2.96

• 2.87• 2.9

• 2.752.56

• 2.7

2050 AD

Best estimate of HAT, plus 0.2mRSL, plus 1.3m storm surge (above m OD Lerwick)

Backed by rising ground, sea level rise forces reorganisation of coastal sediment cells into ever smaller sub-cells, each less able to buffer sediment deficiency.

Natural drivers of coastal erosionSediment supply

• Sediment supply onceplentiful, now exhausted

• Positive sediment budgets,now negative

• Beach and frontal erosion of back beach now chronic

• Impact of sediment deficitas significant as storminessand, probably,more significant than sea level rise.

2. Avoid structural intervention that protects land at expense of beach,

4. Pursue management strategies that conserve coastal sediment,

1. Ideal defence is flexible, mobile beach,

6. Land–use zoning (set-back, realignment, non-intervention) more sustainable than structural intervention,

3. Any structures which inhibit flexibility likely to be expensive, fail in long-term, or need ongoing maintenance commitment,

7. Embed coastal erosion management (ie. Shoreline Management) within more general Coastal Zone Management Strategy.

5. Identify and assess coastal sites at risk from wave hazard andsediment deficit,

Sustainable coastal erosion managementneeds to maintain coastal flexibility viastrategies that promote:

• sediment conservation,

• coastal land-use zoning,

• environmental engineering,

but this demands good environmental data for sites at risk.

Sea level change and Sea level change and tsunamitsunami

Sea level changeSea level changeSea level change in Shetland over the last 10 000 yearsSea level change in Shetland over the last 10 000 yearsSea level change in Shetland over the next centurySea level change in Shetland over the next century

A rapid rise in sea surface levels to A rapid rise in sea surface levels to circa 6000 radiocarbon years BPcirca 6000 radiocarbon years BPA fluctuating rise in sea surface A fluctuating rise in sea surface levelslevels

Sea surface change offshore NW EuropeSea surface change offshore NW Europefrom 9000 radiocarbon years BPfrom 9000 radiocarbon years BP(10200 years BP) after (10200 years BP) after MornerMorner

OnOn deglaciationdeglaciation,, isostaticisostatic uplift took placeuplift took placeIsostaticIsostatic uplift would probably have varied uplift would probably have varied across Shetland, being greater over the across Shetland, being greater over the centre of Shetland ice, probably centre of Shetland ice, probably Mainland, and less to the north and Mainland, and less to the north and possibly southpossibly southIsostaticIsostatic uplift would have been modified uplift would have been modified by sea surface rise across the adjacent by sea surface rise across the adjacent continental shelfcontinental shelfThe effect of The effect of isostaticisostatic movements along movements along the periphery of the Scandinavian ice the periphery of the Scandinavian ice sheet is unknown, but may have involved sheet is unknown, but may have involved crustalcrustal lowering as a lowering as a forebulgeforebulge waswasreduced in heightreduced in heightThe net effect today is unknown, but may The net effect today is unknown, but may have been to result in land depression as have been to result in land depression as isostaticisostatic uplift ceased and uplift ceased and forebulgeforebulgecollapse continued. However, if land collapse continued. However, if land depression is taking place it will be depression is taking place it will be unequal across Shetlandunequal across Shetland

Possible ice limits adjacent to ShetlandPossible ice limits adjacent to Shetlandat circa 11000 BP and 20000 BPat circa 11000 BP and 20000 BP

The graph for Wick is the nearest analogousThe graph for Wick is the nearest analogousgraph to changes around Shetlandgraph to changes around Shetland

The Intergovernmental Panel on Climate The Intergovernmental Panel on Climate Change Third Assessment Report Change Third Assessment Report estimates that the global average sea estimates that the global average sea levels will rise between 9cm and 88cm levels will rise between 9cm and 88cm from 1990 to 2100, the rise accelerating from 1990 to 2100, the rise accelerating after circa 2040. The best estimate is after circa 2040. The best estimate is 49cm49cmRecent work may increase the estimate Recent work may increase the estimate of the total riseof the total riseAlthough these are global figures, and Although these are global figures, and some areas of the world may experience some areas of the world may experience greater or lesser rises, to date no work greater or lesser rises, to date no work has suggested that the sea surface has suggested that the sea surface offshore NW Europe will rise at a lesser offshore NW Europe will rise at a lesser amountamountRecent work is showing that as the sea Recent work is showing that as the sea surface rises, the height of High Water surface rises, the height of High Water Mark increases at an additional circa Mark increases at an additional circa 25% of the rise in inlets and estuaries25% of the rise in inlets and estuariesIn Shetland, the residual In Shetland, the residual isostaticisostatic effects effects may result in the sinking of the land, thus may result in the sinking of the land, thus exacerbating the situation, although this exacerbating the situation, although this is not yet provenis not yet provenTaking these factors together, it is Taking these factors together, it is considered reasonable to conclude that considered reasonable to conclude that the threat of sea level rise in Shetland is the threat of sea level rise in Shetland is greater than in most of the United greater than in most of the United Kingdom, and certainly greater than Kingdom, and certainly greater than anywhere else in Scotlandanywhere else in Scotland

TsunamiTsunami

TheThe StoreggaStoregga Slides and Slides and sites where evidence for sites where evidence for the Holocene the Holocene StoreggaStoreggaSlide tsunami has been Slide tsunami has been foundfound

Section showing sand deposited by the Holocene Section showing sand deposited by the Holocene StoreggaStoreggaSlide tsunami on the east coast of Slide tsunami on the east coast of SullomSullom VoeVoe, Mainland, Mainland

Borehole sections showing the Holocene Borehole sections showing the Holocene StoreggaStoreggaSlide tsunami on both west and east coasts of Slide tsunami on both west and east coasts of UnstUnst, at , at

BurragarthBurragarth andand NorwickNorwick

Submarine slides in the North AtlanticSubmarine slides in the North Atlantic

Submarine slides offshore NW Submarine slides offshore NW EuropeEurope

Submarine slides in the FaeroeSubmarine slides in the Faeroe--Shetland ChannelShetland Channel

Sand layer probably deposited by a tsunami Sand layer probably deposited by a tsunami circa 3000 BP at circa 3000 BP at BastaBasta VoeVoe, Yell, Yell

The location and area affected The location and area affected by the largest instrumentally by the largest instrumentally recorded earthquake to have recorded earthquake to have affected the United Kingdom: affected the United Kingdom: thethe DoggerDogger Bank Earthquake Bank Earthquake of 1931, magnitude 6.1of 1931, magnitude 6.1

SummarySummarySea level rise around Shetland in the future is a virtual Sea level rise around Shetland in the future is a virtual certainty; although the rate and amount are in doubt, they certainty; although the rate and amount are in doubt, they are likely to be greater than anywhere else in Scotlandare likely to be greater than anywhere else in ScotlandTsunami in Shetland have probably occurred on several Tsunami in Shetland have probably occurred on several occasions, but their timing is unpredictable; however even occasions, but their timing is unpredictable; however even small tsunami can be powerful and can inundate lowsmall tsunami can be powerful and can inundate low--lyinglyingareasareasAs sea level rises the likely inundation of tsunami increasesAs sea level rises the likely inundation of tsunami increasesPlanning for the eventualities of sea level rise and tsunami Planning for the eventualities of sea level rise and tsunami could be based upon two timescales. Where sea level is could be based upon two timescales. Where sea level is concerned, the threats need evaluation against forecast concerned, the threats need evaluation against forecast changes (the IPCC Fourth Assessment Report, due in changes (the IPCC Fourth Assessment Report, due in 2005/6 should provide a basis). Where tsunami are 2005/6 should provide a basis). Where tsunami are concerned there is room for further field research before an concerned there is room for further field research before an evaluation of the threats can be madeevaluation of the threats can be made

Storm Hazards: a Shetland perspective

Past

•Meteorology

•Storm chronology

•Natural archives

Future

•Climate change

•Research

Significance of storm tracks

Meteosat animation January 1993

31/1/1953

•Major impact SW and SE Shetland

•Kirkwall also hit

Shetland Storm Chronology

Braer stormSW17/1/1993

131 knot gust on UnstW1/1/1992

Gust to 154 knots, Saxa VordNW16/2/1962

SW27/1/1961

Gust to 109 knots on Costa Hill, Orkney. 33 ms 10 minute gust from N at Lerwick

100-130N31/1/1953

Shetland E coast damage16/02/1900

150W27/12/1862

150±30W10/12/1792

23/10/1669

Storm surge in N SeaNNW10/1634

NoteMax wind speed (knots)FromDate •Recorded from 1900

•Wind speeds from 1922•Reconstructed before 1900

Highest hourly wind speed at Lerwick

0

10

20

30

40

50

60

70

1920 1930 1940 1950 1960 1970 1980 1990 2000

Year

Spee

d (k

nots

)

1953 1961 1992/3

Storm impacts at Lerwick

YesNoNo17/1/1993

YesNoNo1/1/1992

16/2/1962

27/1/1961

YesYesYes31/1/1953

YesYesYes16/02/1900

WindDamage

ErosionInundationDate

1900 storm

Extreme waves on the exposed outer coast of Shetland

Villians of Hamnavoe

cliff

wave quarry site

wave-scoured ramp

boulder beach

older storm boulders embedded in turf

air-borne debris

older storm deposits20 m

100 m

WASAWave heights increased 1955-1994

Wave heights also peaked in 1890s

Positive NAO Index

The Positive NAO index phase shows a stronger than usual subtropical high pressure centre and a deeper than normal Icelandic low.

The increased pressure difference results in more and stronger winter storms crossing the Atlantic Ocean on a more northerly track.

This results in warm and wet winters in Europe and in cold and dry winters in northern Canada and Greenland

More North Atlantic storms?Yes – more energy in the system

No – temperature gradient across Polar Front is less

Most models indicate increased storminess with an increase in mean annual air temperatures in the NE Atlantic. In the 21st century storm intensity will increase, with intensity migrating eastwards across the Atlantic, so becoming greater in the Shetland-Norway area.

STOWASUS-2100Regional STOrm, WAve and SUrgeScenarios for the 2100 century

•Significant local and seasonal variation in sea states

•Increase in significant wave heights in Norwegian waters in winter

•At 60N in North Sea little apparent change even for 100 year waves

Models of changes in wind, surge and wave climate for a world with double CO2 in 2060+

Summary• Historic record demonstrates that major storms present a significant hazard

to the people of Shetland • Impacts may be severe but are often localised by storm tracking and coastal

configuration• Geological record suggests one or more bigger storms than any in the 20th

century occurred in the 17th century and earlier• Global warming will see increased storm activity but unclear if the

magnitude or frequency of the most damaging, extreme storms will change.• Wave heights offshore increased between 1955-1994, with a probable link

to NAO, but latest models do not predict further increases in waters around Shetland with a doubling of CO2

• Key research is needed on the impact of 20th century storm on Shetland, the local storm chronology and on modelling intense depressions in the North Atlantic under global warming

Key Future Research

• Impact of 20th century storms on the coast of Shetland

• Storm chronology for Shetland based on the local geological record

• Modelling of explosive cyclogenesis and associated sea states in a warmed North Atlantic

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