Gualan Island Supplementary Report

GUALAN ISLAND SUPPLEMENTARY REPORT, SOUTH FORD, OUTER
HEBRIDES
Final Report
Ref: TSE/SA/865/68-PE/03
Alastair Dawson, Cristina Gómez and William Ritchie
Aberdeen Institute for Coastal Science and Management (AICSM)
e-mail: [email protected]
University of Aberdeen
October 2010
TABLE OF CONTENTS
Page
1. INTRODUCTION
1.1 Scope of requirement
3
1.2 Geomorphological Processes
3
2. METHODS
6
3. RESULTS
3.1
Lionaclete coastal area
7
3.2
North Gualan and North Channel
9
3.3
Central Gualan Breach
12
3.4
Southern Gualan and South Channel
15
4. DISCUSSION
18
5. FURTHER READING
22
1
GUALAN ISLAND SUPPLEMENTARY REPORT, SOUTH FORD, OUTER
HEBRIDES
Alastair Dawson, Cristina Gómez and William Ritchie
Aberdeen Institute for Coastal Science and Management (AICSM)
University of Aberdeen
1. INTRODUCTION
As described in the first Gualan report, the future evolution of the South Ford area,
between Benbecula and South Uist, will to a large extent be influenced by what
happens to the barrier island of Gualan. Gualan Island is a remnant strip of sand and a
vulnerable barrier island which, in the future, could disappear as a result of the effects
of predicted climate changes and open-up the west side of South Ford to the full range
of Atlantic wave action. The aim of this research project is to add new information on
the evolution of Gualan Island to supplement the information earlier gained through
the analysis of aerial photographs and Lidar data for the period between 1984 -2005.
This new information derives from the analysis of earlier aerial photographs of the
area covering the period between 1946 -1984. These older sets of aerial photography
have the potential to inform us of how this area has evolved since the end of World
War II. This information thus has the potential to provide new insights regarding the
long-term evolution of this barrier island system. Much of the core information on the
dynamics of geomorphological change at Gualan were provided in the first Gualan
report and are not repeated here. In this account the discussion is restricted to new
information arising from the analysis of the older sets of aerial photography. In a few
limited cases where some of the discussion contained within the first report informs
the present discussion, this information is repeated. Much of the discussion of the
changes across Gualan is also related to changes that have taken place over time along
the Lionaclete coastline. There have also been important changes in the shape and
position of the North Channel that separates Lionaclete and Gualan Island. In the text,
all three areas are mentioned since change in one area is nearly always associated with
changes in the other two areas.
As in the previous report, it is unwise to assume that specific measurements of
coastal change have a high level of accuracy. Aerial photographs and maps have
intrinsic limitations within certain variance parameters. These are not included in this
2
report since the scale of change in specific coastal areas is sufficiently large to ensure
that the interpretation of the evidence is relatively secure and fit-for-purpose.
1.1.
Scope of Requirement
A single scope of requirement is considered here:
Arising from previous research on coastal evolution in Scotland by the
Aberdeen research team, changes at Gualan are assessed through an analysis of the
older sets of aerial photography (1946-1965). This information, in turn, is used to reevaluate the nature of the landscape changes that took place between 1984 and 2005.
Digitised data from topographic maps were also used to aid interpretation.
1.2.
Geomorphological Processes
For more than 5-6,000 years, Gualan and the South Ford area have evolved into its
present position as a late stage in the generally accepted model of machair
development. Gualan Island is the last vestige of an extensive, low-lying machair
landscape that once occupied most of the west side of the present South Ford intertidal strand. Sea level rise and flooding (probably from the east) has left Gualan as the
remnant dune ridge of an ancient machair system. Small isolated fragments of
machair remain in the South Ford basin as well as extensive areas of inter-tidal peat.
These are particularly well-developed on the Borve and Lionaclete foreshore areas.
They show that along the Atlantic margin several thousand years ago, a dune ridge
must have laid several hundred metres west of the present-day Gualan Island. Coastal
processes, sea level rise and sediment deficiency, have led to a progressive shoreline
retreat. At the same time flooding and erosion have removed the low unprotected
machair as a result of sea encroachment from the Minch to the east. This process of
shoreline retreat has continued up to present and is almost certain to continue in the
future.
3
Plate 1 View, looking north, from north end of Gualan across the North Channel
towards Lionaclete. Note the recurved gravel spit in the foreground, believed to have
been produced during the Great Storm of January 2005.
The pattern of longshore drift of sand dictates that the net direction of drift
along the Atlantic beach systems and in shallow water offshore is northwards with
local variations produced by the sheltering effect of headlands to south and north of
the South Ford embayment. Uneven subtidal features such as rock reefs also affect
this pattern of longshore drift. The movement of shingle is quantitatively different
from the sand beaches. Movement of shingle mostly occurs during high tides and
especially during storms. Beach shingle occurs discontinuously along the length of the
coastline. Some spreads are relatively low, flat and superficial, others are represented
as backshore storm ridges while other deposits underlie, occur within, and rest on top
of the coastal sand dunes and machair. Washover across coastal dune and machair
areas occurs during storms that are coincident with high tides (for example during the
January 2005 storm). During quiescent periods between major storms, coastal dune
ridges such as Gualan may accrete and rebuild. Nevertheless, the areas in the dune
system that were subject to washover in an earlier storm, remain as vulnerable parts of
the barrier island and are susceptible to future washover events.
The photograph images contained in this report illustrate the washover events
that occurred in the storm of 2005 as well as their effects on the coastline.
4
Examination of the aerial photographs used in this report also indicate that washover
events have occurred historically during numerous winters and should therefore be
regarded as normal, rather than exceptional processes. Washover of sand and shingle
is normally a unidirectional transfer of sediment to the lee side of the dune ridge. In
the Gualan area, washover also takes place in conjunction with tidal changes. For
example, in the South Ford basin these processes have resulted in the production of
characteristic flat lobes or fans of sediment located in the lee of Gualan Island. Over a
timescale of years, the processes of washover have added to the volume of sediment
that occupies the wide inter-tidal strand between Gualan, Benbecula and South Uist.
This has, in turn, affected inter-tidal drainage patterns. During winter storms,
washover events have breached across sections of Gualan Island. If such events
continue in the future, breaches may develop that ultimately fragment the barrier
island into one or several segments. To date this has not happened at Gaulan since
incipient breaches have been quickly re-sealed by post-storm longshore drift as well
as by aeolian deposition. In 2010 it was clear that since 2005 some washover areas
remain vulnerable to overtopping and to possible breaching during future storm
events.
Plate 2 View, looking north, along the middle section of Gualan Island. Note
in the foreground that the coastal barrier has no vegetation cover and is lower than
surrounding areas of the coastal barrier. This is an area that has recently been
overtopped by storm waves and is likely also to be overtopped in the future.
5
The combination of these complex patterns of tidal flow with the South Ford
causeway has been described in both the JBA numerical modelling report and in the
first South Ford report on recent coastal change. In this report, we describe patterns of
coastal change that have taken place in the Gualan area between AD 1946 and
present. This report therefore adds new information to the earlier report that focused
on the measurement of coastal change between AD 1984 and 2006. The longer
timescale considered here thus provides valuable information on the nature and scale
of coastal changes that took place during a 38-year time interval starting at the time of
the first air photo survey by the RAF in AD 1946 and ending with the air photo
imagery that was flown in AD 1984 at approximately the same time as the
construction of the South Ford causeway.
2. METHODS
For analysis of longer term changes that have occurred over the last 200 years,
historical maps dated 1805, 1878, and 1965 provide valuable sources of information.
These maps were scanned for the earlier report and relevant elements for analysis,
such as MHWM (Mean High Water Mark) digitized. Comparison of the planimetric
location of the MHWM at different dates allowed interpretation of changes and
processes for the Gualan Island area.
In this report we make use of various sets of historical aerial photography
(Table 1.1) which were found in TARA (The Aerial Reconnaissance Archive) in
Edinburgh. Digital copies of this photography were obtained from the archive and
visually interpreted and compared with recent photography. Table 1.1 shows a list and
some details of the photography used. These photo images of ‘older’ Gualan
landscapes are discussed in this report. Owing to the relatively poor quality of some
of the aerial photographs, the imagery cannot be subject to a rigorous quantitative
analysis. Instead, the photographs have an intrinsic value in providing supplementary
sources of information to enable checking of the validity of other map and
photographic measurements.
6
Table 1.1 List of historical aerial photography used in this report. Source: TARA
(The Aerial Reconnaissance Archive).
Photo code
Date
Scale
CPE_UK_0189_1376
10/10/1946
1:10000
CPE_UK_0189_3390
10/10/1946
1:10000
CPE_UK_0189_3391
10/10/1946
1:10000
CPE_UK_0191_4051
10/10/1946
1:10000
CPE_UK_0191_4053
10/10/1946
1:10000
OS_63_062_035
24/05/1962
1:27000
OS_63_146_018
01/07/1963
1:27000
OS_65_072_001
01/05/1965
1:5000
OS_65_072_074
01/05/1965
1:5000
OS_65_090_067
13/05/1965
1:5000
In this report we present a series of maps each of which illustrate patterns of
landscape change across the Gualan – Lionaclete area since 1946. GIS software has
been used to display the air photo images at the same scale and with approximately
the same size. Each image is framed by the same latitude and longitude coordinates
with each oriented to grid North. These procedures enable direct comparisons
between the images and thus make it possible to draw inferences on patterns of
coastal change and relate these to the 1984 and 2006 imagery described in the earlier
report. These older images are described below.
2. RESULTS
3.1.
Lionaclete coastal area
The 1878 Ordnance Survey map serves as a useful reference to understand the
patterns of coastal change that have taken place in the Gualan –Lionaclete area over
the last century (Figure 3.1). This map also provides a valuable context in which to
understand patterns of coastal change that have taken place between 1946 -1984.
Remarkable changes in the position and shape of Gualan over the last ca. 130 years
are evident. For example, the northern end of Gualan was, during 1878, located nearly
500 m south of its present position. Given the more southerly position of the
Lionaclete coastline at this time, one can envisage a 200-250 m wide tidal strait (the
North Channel) through which Minch and Atlantic waters were exchanged. Not only
7
was the northern end of the barrier island located much further south but the Atlantic
shoreface of the island was located ca. 100 m west of its present position (Figure 3.1).
Figure 3.1 Coastline change during last 200 years.
Coastline positions drawn from the aerial photography flown in 1946 and from
the Ordnance Survey map for 1965 are also plotted on Figure 3.1. The position of the
HWM lines for this period shows that continued erosion along the northern flank of
the North Channel had taken place between 1878 and 1965. It is inferred, therefore,
that during this time, the position of this channel was located where the most northern
spit occurs at present. In Figure 3.2 visual comparison of the Lionaclete area at four
dates during the last century points to an increase in the rate of coastal erosion
between 1984-2006. Fields of crops first evident in the 1946 image, appear to have
been eventually abandoned (Figure 3.2). For example, several fields are clearly shown
due west of the drainage ditch in the 1946 and 1965 photography. The fields appear to
have been abandoned by 1984. By 2006 about only half of the original coastal
landscape remains. These changes also appear to have been accompanied by a
progressive northward displacement of the North Channel (eg. compare the channel
positions for 1946 and 2006).
8
Figure 3.2. Coastline reconstruction at the Lionaclete area. The blue line marks the
position of MHWM in 2006. Note the field areas of crops shown in 1946 and 1965
that appear later to have been abandoned, in some areas mantled by blown sand.
3.2.
North Gualan
The north end of Gualan Island has experienced a change in its shape and extension
between 1946 and 1965 (Figure 3.3). For example, the Atlantic shoreface has been
progressively eroded, has been subject to retreat and has undergone realignment. All
of these processes have led to coastal retreat and shoreface re-deposition of sediment
(see section on geomorphological processes). The photography shows clearly that the
9
rate of shoreline change has increased during the period 1984-2006. It is quite clear
that although coastal change continued to take place between 1946 and 1965, such
changes were small by comparison with those that took place after 1984.
Plate 3 View of same area described in Plate 2 but from seaward to landward. The
part of the coastal barrier that is topographically lower also has a surface cover of
seaweed, demonstrating recent overtopping by waves.
Comparison of the 1946 and 1962 photography shows that the coastal retreat
on the Atlantic shore of the northern section of Gualan island has triggered a
noticeable reduction of its width (highlighted with the green and pink lines in Figure
3.3). This width decrease led to an apparent change in shape, towards a more
elongated form. The 1962 and 1963 images show little alteration, but a clear change is
evident in the 1965 imagery where a new spit appears to have formed at the northern
end and to have been of sufficient size to have led to a displacement in the course of
the North channel. One might even argue that by 1984, this spit had been partially
truncated only to have experienced renewed growth by 2006.
10
Figure 3.3. Evolution of the coast in the north Gualan area from 1946 to 2004.
Symbols are described in the text.
11
It should be noted that all changes at the "gap" between Gualan and Benbecula
are caused by a complex and variable interplay of two main coastal processes- wave
driven longshore sediment drift and tide driven ebb and flood water movements
between the Atlantic and the South Ford tidal basin. This is also compounded by tidal
flows to and from the Minch and to a lesser extent the variable amounts of fresh water
added to the basin from controlled drainage from South Uist and Benbecula. These
processes are controlled by changing gradients between water levels within and
outwith the South Ford basin and also by the pattern of inter-tidal drainage channels
in South Ford, including an effective "watershed" that appears to lie, not surprisingly,
along the line of the old track across the sands. The velocities of inwards and
outwards flows at the north end of Gualan can be very powerful and are affected by
the changing cross sectional area of the "gap". Although Figure 3.3 depicts changes to
High Water Mark, it is also useful to look at changes in the inter tidal morphology and
Low Water Mark as a reminder that for most of the tidal cycle a range of dynamical
geomorphological changes are taking place.
3.3.
Central Gualan Breach
Visual inspection of the central area of Gualan Island suggests the existence of some
areas where Atlantic storms have crossed the barrier island prior to the severe event of
January 2005. In the 1946 photography, the north-south trending coastal dune edge
appears to be characterised by continuous sections of vegetation (marram) separated
by occasional areas of bare sand (Figure 3.4). In marked contrast, the 1962
photograph shows the majority of the central coastal strip covered by bare sand. Most
of the areas of vegetation visible in the 1946 photographs have disappeared. This area
of sand cover is shown in Figure 3.4 as a linear stretch of terrain between location A
in the north and the prominent area of marram-covered dune shown as B in the south
of the area (Figure 3.4). In the succeeding photographs one and three years later (1963
and 1965) this strip of sand has disappeared and is replaced by a near-continuous
cover of coastal vegetation. We therefore infer that a major episode of storminess
affected the Central Gualan area, most probably during the winter of 1961-62. By
1984 this area exhibits a near-continuous vegetation cover but is later completely
covered by sand and gravel by 2005. It should also be noted that area B appears to
have experienced its greatest erosion sometime between 1984 and 2006. We infer
12
here that coastal erosion of this particular area is most likely to have taken place
during the 2005 storm. Finally, it should be noted that the strip of marram-clad coastal
dune shown as A in the 2006 image is also represented in part in the 1946 image
suggesting that position of the MHWM in this area has not changed greatly over this
time interval. The area in the yellow circle (Figure 3.4) appears with a more extensive
aerial cover of sand in 1962 than at any other date. Apart from local significance, this
rocky area, shown within the yellow circle, provides valuable fix-points for the
photographs and serves as an aid in comparison between the different photo images.
13
Figure 3.4 Central breached area of Gualan Island. Letters and symbols are
described in the text.
14
3.4.
Southern Gualan and South Channel
In the southern part of Gualan Island there have been remarkable coastal changes over
the time period between 1946 and 1984. These include a marked reduction in width of
the channel since 1946 (Figure 3.5, A), together with a displacement of the most
southern part of the spit (Figure 3.5, C). The southern area of marran-covered dunes
was separated from an area of salt marsh (validated in the field) by an area of bare
sand until 1984 (shown as a pink line on the 1963 photo in Figure 3.5). This line is replotted on the 2006 photo. The position of the Atlantic coast line (green line in Figure
3.5) appears to indicate quite clearly that there has been a net shoreface recession in
this area between 1963 and 2006. Area B in Figure 3.5 shows a sporadic sand
coverage of the vegetated southern area.
Plate 4 View, looking northwards, along the Gualan coastal barrier showing recent
seaward erosion of the coastal dunes.
15
Over the last ca. 60 years there has also been a marked reduction in the size of
the tidal channel that separates the southern end of Gualan from the north coast of
South Uist. The channel is clearly marked in the 1946 image and it is a very clear
feature in the 1962 image. It is also evident in the 1963 photo although here the green
line (showing the extent of coastal dune cover in 1962) shows that also in this area
there has been a limited amount of coastal progradation between 1962 and 1963. The
channel is also a clear feature in the 1965 photograph (area A) but it is a narrower and
shallower feature in 1984. Shallow sand bars are also visible within the channel on the
1984 photograph. It is perhaps also worth noting that the route of this channel changes
between 1965 and 1984. Whereas in the 1965 image, the part of the channel seaward
of Gualan Island changes direction from NW-SE to N-S, this pattern is not evident in
the 1984 image where the route of the channel trends almost continuously between
NW-SE along its entire length. It is not immediately clear why this should be,
although it is reasonable to infer that this change may be related to a long-term build
up of sediment in this area. It seems that after the 2005 storm, this southern area was
more affected than in previous events, with wave overtopping having affected the
eastern side more than in 1962 (yellow arrows in 1962 and blue arrows in 2006;
Figure 3.5).
16
Figure 3.5. Southern Gualan and South Channel. Letters and symbols are described
in the text.
17
4. DISCUSSION
A key difficulty encountered in the first Gualan report was how to interpret the coastal
changes that took place between 1984 and 2006. The simplest explanation was to
consider that the patterns and rates of change in the Gualan coastal landscape took
place progressively and uniformly over the 22-year time interval between the two
dates. The difficulty with this interpretation is the knowledge that the Great Storm of
January 2005 was associated with major and relatively rapid changes in the coastal
landscape. The decision to commission new airborne imagery several months after the
storm had as its objective the need to make new maps of the coastal landscapes of
South Uist and Benbecula. It was never possible, however, to be sure just how much
of the observed coastal changes were attributable to the January 2005 storm. The use
of aerial photography dating back to 1946 allows this question to be answered in part
since, by inspecting the patterns of coastal change that took place between 1946 and
1984, it enables one to make an assessment of whether or not the changes that took
place over this time interval are greater or less than those that occurred between 1984
and 2006.
Plate 5 View, looking north, along the Gualan coastal dune ridge. Note the low relief
that characterises the ridge as well as the broad low areas of vegetated sand that
occur to the rear. The low relief of this area is an indication of the vulnerability of
this area to erosion, overtopping and breaching by storm waves.
18
In the earlier report the 5 major changes listed below were identified and based
on a comparison of the 1984 and 2005 DTMs. Summaries of the observed changes
that have taken place between 1946 and 1984 are also provided below.
• Since 1984 the seaward edge of Gualan appears to have retreated to the east
with the greatest amount of retreat in the north and decreasing from north to
south. The 1946-1984 data appear to indicate that shoreface retreat during this
period was much less than between 1984-2006. This is particularly evident on
comparison of the 1946, 1965 and 1984 imagery.
• Sediment accretion (build up) has taken place in two areas since 1984. The
first of these has been at the extreme northern end of the island where a gravel,
sand and boulder spit (that did not exist in 1984) presently extends to the NE
towards the edge of the North Channel. To the south, the spit is attached to
high (5-10 m) vegetated dunes that comprise a complex area of undulating
marram-dune topography that also includes evidence of discrete stages of
growth. With one exception the older photograph shows no evidence of spit
formation at the northern end of Gualan. The exception is the 1965 photograph
where a clearly-developed elongate and S-N trending spit is visible at the
northern end of Gualan. This feature is approximately half the size of the
comparable feature shown on the 2006 imagery.
• A second zone of accretion has taken place between 1984 and 2006 at the
extreme south of the barrier island. This zone consists of two distinct
topographic areas. To the rear of the southern end of Gualan, there is an area
of sand accretion that effectively blocks the movement of tidal waters between
Gualan and the northern coastline of South Uist. The second area of accretion
consists of the sand dunes themselves, these having accreted vertically since
1984 forming a stable barrier of vegetated sand. The 1946-1984 photographs
show a clearly-defined channel separating Gualan from South Uist. This
channel is particularly clear in the oldest photography but there are indications
on the 1984 photograph of this channel having started to become narrower.
This is a significant observation since it demonstrates that there is no simple
19
cause-effect relationship between the construction of the causeway and the
near-closure of this channel.
• In the extreme north of the area, complex changes have taken place between
1984 and 2006 with areas of extensive erosion having occurred adjacent to
areas of substantial accretion. The most extreme sediment loss has been on the
Benbecula side of the North Channel adjacent to Lionaclete. However, the
photography from 1946 to 1984 also shows major changes having taken place,
for example loss of land along the Lionaclete coastline, as well as major
changes in the position of the North Channel. Here also, these observed
changes are significant since they took place before the causeway was built.
• Many observations have drawn attention to the scale of wave overtopping
during the January 2005 storm that led to the near-breaching of Gualan at
several locations. This analysis has shown that similar event/s may have taken
place prior to the flying of the 1962 photographs during May of that year. The
1962 photography shows the disappearance of a coastal dune vegetation cover
over long sections of the Atlantic coastal edge and its replacement by a nearcontinuous strip of sand (and presumably also gravel and shingle). The next
oldest photography is for 1946. Hence, all that can be concluded based on the
photographic data is that a major storm/s took place sometime during this time
interval. The time series of daily air pressure for Stornoway provides
additional information (Figure 3.6). This analysis of differences in daily air
pressure (dp(24)abs) (Hanna pers. comm.) points to 1962 as an exceptionally
stormy period and is consistent with the photographic evidence. Whatever the
precise cause of the extensive sand cover across Gualan in the 1962
photograph, this information points to the former occurrence of major storms
in addition to the 2005 event sufficient to cause major changes in the
landscape of Gualan Island. Other even older major storms have already been
described for AD 1921 and AD 1869 (Dawson et al. 2007). These
observations have additional significance since they demonstrate that the
January 2005 storm has not been the only major destructive storm during the
last ca. 130 years to have led to severe damage and significant change to the
Gualan Island barrier system.
20
Figure 3.6 Annual pressure variability, Stornoway, 1921-2003. Higher values (mb)
indicate periods of increased winter storminess (courtesy of Hanna, unpublished
data)
Possibly, in the future, the remnant barrier island of Gualan will ultimately
disappear to produce an open strait between the Atlantic and the Minch. This future
tidal strait will probably be similar in many respects to the ‘gaps’ between Barra and
South Uist and between Berneray and Harris, but with a transverse barrier in the form
of a causeway. Over the short term, however, Gualan will alter its shape and position
in response to changes in wave dynamics, longshore drift, tides, and sea level
changes. A deficiency in the availability of nearshore sediment will continue to be the
most important controlling and irreversible factor. Aeolian (wind) processes will
continue to build coastal dunes along the Atlantic margin but these areas are likely to
reduce in size and extent given a diminishing source of sediment supply offshore.
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5. FURTHER READING:
Dawson, A.G. and Dawson, S. (2005) Western Isles Coastal Zone Assessment
Survey, Benbecula and South Uist, Commissioned Report for EASE Archaeology and
Historic Scotland, 125 pp.
Dawson A.G., Dawson, S and W Ritchie (2007) Historical Climatology and coastal
change associated with the 'Great Storm' of January 2005, South Uist and Benbecula,
Scottish Outer Hebrides, Scottish Geographical Journal, 123, 2, 135 – 149.
Dawson, A.G., Ritchie, W.A., Green, D., Wright, R., Gomez, C. and A Taylor (2008)
Assessment of the rates and causes of change in Scotland’s beaches and dunes –
Phase 2, Commissioned Report for Scottish Natural Heritage, Account No. SM002
RGC1479.
DEFRA report and data:
http://www.defra.gov.uk/environ/fcd/pubs/pagn/climatechangeupdate.pdf
Gómez, C., Taylor,A., Green,D., Ritchie,W., Dawson,A., and R.Wright (2008)
Terrain 3D modelling for the assessment of coastal change in beach and dune systems
in Scotland. SOC Bulletin, n.42.
Jonsson, T. And E Hanna 2007 A new day to day pressure variability index as a
proxy of Icelandic storminess and complement to the North Atlantic Oscillation
Index, 1823-2005, Meteorologische Zeitschrift, 16, 1, 25-36.
Hanna, E.,Cappelen, J., Allan, R., Jonsson, T., Le Blancq, F., Lillington, T. And K.R.
Hickey 2008 new insights into North European and North Atlantic surface pressure
variability, storminess and related climate change since 1830, American
Meteorological Society, 21, 6739-66.
Lowe, J.A. et al. (2009) UK Climate Projections science report: marine and coastal
projections. Met. Office Hadley Centre, Exeter, UK, ISBN 978-1-906360-03-0.
Maune, D.F. (2006) Digital elevation model technologies and applications: The DEM
users manual, 2nd edition
Note: all maps used within this report were printed under licenses held by the
University of Aberdeen for research purposes.
22