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Coastal Processes and Morphological Change in the Dunwich-Sizewell Area, Suffolk, UK

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PYE, K. and BLOTT, S.J., 2006. Coastal processes and morphological change in the Dunwich-Sizewell area, Suffolk, UK. Journal of Coastal Research, 22(3), 453–473. West Palm Beach (Florida), ISSN 0749-0208. The Suffolk coast around Dunwich and Sizewell has experienced major changes during the past 2000 years, with significant loss of land caused by marine erosion. Against a background of projected acceleration in sea level rise and storminess resulting from global climate change, concern has been expressed that present coastal defences may become unsustainable in the medium to longer term, and that the survival of internationally important wildlife habitats is under threat. This paper examines the past coastal evolution in the light of natural processes, and provides a discus-sion of future management options. Based on analysis of historical maps, charts, air photographs, and ground survey data, it is shown that rates of coastal erosion have actually been much lower in the last 50 years than historically, and at present there is little scientific evidence to support a case for large-scale managed realignment or abandonment of flood and coastal defences. However, in some areas, notably the very northern end of the Minsmere barrier and the middle part of the Dunwich-Walberswick barrier, local realignment and/or construction of stronger secondary flood defences are required to establish a coastal condition that is more in equilibrium with current processes, and to provide adequate protection against marine flooding even under present climatic and sea level conditions.
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Journal of Coastal Research 22 3 453–473 West Palm Beach, Florida May 2006
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Coastal Processes and Morphological Change in the
Dunwich-Sizewell Area, Suffolk, UK
Kenneth Pye and Simon J. Blott
Kenneth Pye Associates Ltd
Crowthorne Enterprise Centre
Crowthorne Business Estate
Old Wokingham Road
Crowthorne, Berkshire RG45 6AW, United Kingdom
k.pye@kpal.co.uk
ABSTRACT
PYE, K. and BLOTT, S.J., 2006. Coastal processes and morphological change in the Dunwich-Sizewell area, Suffolk,
UK. Journal of Coastal Research, 22(3), 453–473. West Palm Beach (Florida), ISSN 0749-0208.
The Suffolk coast around Dunwich and Sizewell has experienced major changes during the past 2000 years, with
significant loss of land caused by marine erosion. Against a background of projected acceleration in sea level rise and
storminess resulting from global climate change, concern has been expressed that present coastal defences may become
unsustainable in the medium to longer term, and that the survival of internationally important wildlife habitats is
under threat. This paper examines the past coastal evolution in the light of natural processes, and provides a discus-
sion of future management options. Based on analysis of historical maps, charts, air photographs, and ground survey
data, it is shown that rates of coastal erosion have actually been much lower in the last 50 years than historically,
and at present there is little scientific evidence to support a case for large-scale managed realignment or abandonment
of flood and coastal defences. However, in some areas, notably the very northern end of the Minsmere barrier and
the middle part of the Dunwich-Walberswick barrier, local realignment and/or construction of stronger secondary
flood defences are required to establish a coastal condition that is more in equilibrium with current processes, and to
provide adequate protection against marine flooding even under present climatic and sea level conditions.
ADDITIONAL INDEX WORDS:
Cliff erosion, shoreline retreat, sea level rise, storm surge.
INTRODUCTION
Recent decades have seen increasing concern in many parts
of the world about the implications of future shoreline change
for human communities and nature conservation interests.
Predictions of accelerated sea level rise and possible in-
creased storminess related to global warming over the next
century have been linked to increased risk of coastal erosion
and flooding. If such predictions prove to be accurate, present
flood defences and coast protection works in many areas will
become unsustainable, and important ecological habitats will
be severely damaged or lost. Consequently, there is a need to
review future management options and subsequently to im-
plement strategies that allow for the uncertainties associated
with possible future coastal change. In order to inform this
debate, it is essential that there is an adequate understand-
ing of past coastal change, current coastal processes, and the
constraints imposed by geological and other factors on the
capacity of any given section of coast to respond to changes
in forcing factors.
This paper reports the findings of a study carried out to
quantify the nature and rates of past coastal changes in the
Dunwich-Minsmere-Sizewell area of Suffolk, to assess the
controls on present coastal processes, and to provide back-
ground information against which options for future coastal
DOI:10.2112/05–0603.1 received 18 October 2005; accepted 19 Octo-
ber 2005.
management can be assessed. The study area is arguably one
of the most scenically attractive and least spoiled in England.
It contains several sites that are of national and international
importance for nature conservation, including the Royal So-
ciety for the Protection of Birds (RSPB) Minsmere Reserve.
The area also contains one of the country’s largest nuclear
power complexes at Sizewell. The methods employed in the
study included a review of published and unpublished infor-
mation, analysis of historical maps, charts and air photo-
graphs within a geographic information system (GIS) frame-
work, modelling using LIght Detection And Ranging (LIDAR)
data, and analysis of field survey data gathered over several
years.
GEOLOGICAL BACKGROUND TO
THE STUDY AREA
The study area (Figure 1) lies on the western margin of the
Southern North Sea Basin, an area that is currently experi-
encing slow subsidence as a result of both regional tectonic
factors and the collapse of a proglacial forebulge (L
AMBECK
,
1995; S
HENNAN
, 1989). However, in the geologically recent
past, the onshore area of eastern East Anglia has experienced
periods of relative uplift, probably because of block tilting and
crustal deformation caused by loading in the southern North
Sea Basin (F
UNNELL
, 1996). The ‘‘solid’’ geology of the Suffolk
coastal region consists mainly of Pliocene and Pleistocene age
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Figure 1. Location of the study area, showing the main locations re-
ferred to in the text.
Figure 2. Simplified geological map of the area around Dunwich and
Sizewell (based on British Geological Survey 1:50,000 sheets), showing
the main areas of sediment input to the coastal system.
sediments and weakly cemented sedimentary rocks, notably
the Coralline Crag (Pliocene) and the Red Crag and the Nor-
wich Crag (Pleistocene) (H
AMBLIN
et al., 1997; Figure 2). Sev-
eral subdivisions have been identified within the Norwich
Crag, including the Chillesford Sand, the Easton Bavents and
Chillesford Clays, and the Westleton Beds. The Crag deposits
are mainly shallow marine, coastal, and estuarine in origin,
having been deposited during a period of relative sea level
and shoreline fluctuations, probably superimposed on longer-
term tectonic tilting (F
UNNELL
, 1996; H
EY
, 1967, 1982;
M
ATHERS
and Z
ALASIEWICZ
, 1988, 1996; S
INCLAIR
, 1999).
The Westleton Beds are particularly coarse, being previously
known as the ‘‘Westleton Sands and Shingle,’’ the ‘‘Pebbly
Sands,’’ or the ‘‘Westleton Series’’ (P
RESTWICH
, 1890; S
OLO
-
MON
, 1935); they probably represent nearshore and shoreface
facies. The Westleton Beds form an extensive spread inland
from Minsmere and Dunwich Cliffs. The northern part of the
Dunwich Cliffs is comprised mainly of sands, with scattered,
thinner units composed of sandy gravel, forming part of the
Norwich Crag. The older, Coralline Crag is locally cemented
and generally more resistant to erosion; it forms a SW-NE
trending ‘‘high’’ that extends offshore from Thorpeness and
outcrops on the adjoining seabed. The presence of more re-
sistant material in this area is probably largely responsible
for the maintenance of a slight promontory at Thorpeness
that forms low cliffs cut into Lowestoft Till.
Onshore, ‘‘drift’’ deposits that lie above the Norwich Crag
consist mainly of ‘‘boulder clay’’ and fluvial deposits belonging
to the Lowestoft Till Formation, with deposits of Holocene
alluvium and peat within the modern valleys (Figure 2). Un-
til the Middle Ages, a number of small estuaries existed;
these are now cut off from the sea by shingle and sand barrier
systems. The estuaries were formed as a result of early to
mid-Holocene flooding of river valleys that were cut to a low-
er level during glacial low sea level stands. Following marine
transgression during the early Holocene, sequences of ma-
rine, brackish, and freshwater sediments accumulated, in
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Table 1. Predicted tide and measured storm surge levels, in metres above Ordnance Datum, for nearby stations. Source: Admiralty Tide Tables 2004 (United
Kingdom Hydrographic Office, 2003) and Steers et al. (1979).
Port
Lowest
Astronomical
Tide
Mean
Low Water
Springs
Mean
Low Water
Neaps
Mean
Sea Level
Mean
High Water
Neaps
Mean
High Water
Springs
Highest
Astronomical
Tide
1978
Storm Surge
1953
Storm Surge
Lowestoft
Southwold
Minsmere Sluice
Aldebergh
Felixstowe
2
1.50
2
1.30
2
1.60
2
1.60
2
2.05
2
1.00
2
0.80
2
1.30
2
1.30
2
1.55
2
0.50
2
0.40
2
0.80
2
0.70
2
0.95
0.11
0.25
2
0.19
0.06
0.15
0.60
0.80
0.40
0.70
1.15
0.90
1.10
0.80
1.10
1.85
1.40
1.60
1.30
1.60
2.25
2.00
2.45
3.50
3.78
places up to 10 m thick (e.g., B
REW
,F
UNNELL
, and K
REISER
,
1992). Significant areas around the margins of these estu-
aries have been reclaimed, principally since medieval times.
COASTAL PROCESSES
Tides
Tides on the Suffolk coast are semidiurnal, with an average
progression of approximately 30 minutes between successive
tides. Predicted tidal levels for standard and secondary ports
are shown in Table 1. The mean spring tidal range decreases
northwards from Felixstowe, reaching a minimum of 1.9 m
at Lowestoft. The level of predicted high waters relative to
Ordnance Datum (OD) reaches a minimum near Minsmere
(ca. 0.8 m OD at springs and ca. 0.4 m OD at neaps).
The flood tidal stream offshore runs almost south (ca. 185
8
)
subparallel to the coast (A
DMIRALTY
, 2004). Average tidal
current velocities reach a maximum 5 hours before high wa-
ter, at 0.67 m s
21
on spring tides and 0.31 m s
21
on neap
tides. The ebb tidal stream runs almost northwards (ca.
007
8
). Average velocities reach a maximum 1 hour after high
water, 0.72 m s
21
on spring tides and 0.36 m s
21
on neap
tides. R
OBINSON
(1966) emphasised the importance of resid-
ual currents in relation to shoreface evolution on the East
Anglian coast, but modelling studies by H
ALCROW
M
ARITIME
(2000a, 2000b, 2000c, 2000d, 2000e) suggested that current
residuals off the Dunwich-Sizewell coast are very small, al-
though directed southwards. The maximum residual flow
reaches 0.05 m s
21
over Dunwich Bank and near the shore
along the Dunwich Cliffs. Elsewhere, residual flows are less
than 0.05 m s
21
.
Winds
The nearest station for which long-term annual average
wind data are available is at Hemsby, near Great Yarmouth
(Figure 3). Records from 1981 to 2000 show that the prevail-
ing winds blow from the southwest and the calculated resul-
tant is directed towards the northeast. Although winds from
all directions are able to influence aeolian sand transport
along the shoreline, transport of sand from the beach occurs
only when winds blow from the northeasterly, easterly, or
southeasterly directions.
Waves
No long-term measured inshore wave records are available
for this coast, although wave recorders have been deployed
at several locations for short periods at varying times. The
Institute of Oceanographic Sciences installed wave recorders
along the coast and on the offshore banks between 1975 and
1979 (F
ORTNUM
and H
ARDCASTLE
, 1979), the Environment
Agency recorded waves at the entrance to the Blyth Estuary
in 1995–1996, and the Centre for Environmental Fisheries
and Aquaculture Science installed a gauge offshore from Si-
zewell in 2003. An indication of the average offshore wave
regime is provided by the results of hind-cast modelling using
measured wind data. Calculations for a point 48 km east of
Dunwich, produced using The Meteorological Office UK Wa-
ters Wave Model and wind data for the period 1986–1999,
are shown in Figure 3. The data show clear bimodality, with
most waves approaching from the north and northeast (345
8
045
8
) or south and southwest (165
8
–225
8
). Wave energy can
be classified as moderate, with 37.7% of all waves being less
than 1 m high and 76% of all waves less than 2 m high. The
highest waves approach from the north and northeast, which
is the direction of longest fetch. Consequently there is a po-
tential, although relatively small, wave-generated current re-
sidual towards the south (A
NGLIAN
W
ATER
, 1988a, 1988b;
H
ALCROW
M
ARITIME
, 2000a, 2000b). The highest waves are
predicted to approach the coast from the north and northeast,
with 1 in 100 year heights predicted to be 7.3–7.8 m, respec-
tively. The predicted 1 in 100 year wave heights from other
directions range from 5.4 to 6.7 m. The highest waves pre-
dicted to occur during any 1 year are 5.0 m from a northerly
direction and no more than 4.3 m from any other direction.
However, local inshore wave heights, period, and approach
angle are strongly controlled by the morphology of the coast-
line, and by the offshore bathymetry.
The importance of Dunwich and Sizewell Banks (Figure 3)
in reducing wave energy reaching the coast has been a matter
of some debate. R
OBINSON
(1980) concluded that a reduction
in cliff erosion rates observed in the last fifty years could be
attributable to the growth of these banks. He showed that
the northward extension of Dunwich Bank altered the angle
of wave approach and wave height at the coast. Tracer ex-
periments (L
EES
, 1980, 1981, 1983) also demonstrated that
sediment is moved landwards by wave action, resulting in a
landward shift in the position of the banks, during stormy
conditions.
The effect of the banks on wave activity was investigated
between 1975 and 1979 when three wave recorders were in-
stalled close to the shore at Southwold, Dunwich, and Alde-
burgh (F
ORTNUM
and H
ARDCASTLE
, 1979). No significant re-
duction in wave energy could be detected over this period at
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Figure 3. Simplified bathymetric chart of the offshore area around Dunwich and Sizewell. Also shown are the locations of the Environment Agency
beach and nearshore survey profiles referred to in this paper, and the bodies responsible for sections of the coastline. The rose diagrams show the average
wind climate for the period 1981–2000 recorded at Hemsby, near Great Yarmouth, and the modelled wave climate for the period 1986–1999 at a point
48 km offshore. Data sources: Admiralty (2004), The Meteorological Office, and Halcrow Maritime (2001b).
Dunwich, despite the location of the recorders behind the off-
shore banks. However, studies in 1978–79 using wave rider
buoys placed on either side of Sizewell Bank showed that
large waves (
.
2.2 m in height) broke on the offshore banks,
which thereby provided a degree of protection to the coast
(C
ARR
, 1981). By contrast, computer modelling by H
ALCROW
M
ARITIME
(2000a) suggested that the banks are not very im-
portant in terms of the energy that reaches the shoreline un-
der moderate wave conditions. The H
ALCROW
model was ini-
tially run for a spring tide with waves approaching shore-
normal (105
8
) and with the most recent available bathymetry.
The model was then rerun removing Dunwich and Sizewell
Banks entirely from the bathymetry. Results showed that the
banks locally reduce wave heights by up to 0.5 m, but their
effect on wave heights at the shoreline was predicted to be
negligible. However, this study only considered one set of
wave conditions with a fixed angle of approach. Although the
banks may have little influence on waves at the shoreline
during typical weather conditions, they may be far more im-
portant in sheltering the coast during storms, or when waves
approach from other directions.
Storm Surges
The Suffolk coast is frequently affected by surges that
change the height and duration of predicted tidal levels. Pos-
itive surges are most frequently associated with slow-moving
depressions in the North Sea that draw down a strong north-
erly or northeasterly airflow. This has the effect of ‘‘piling’’
water against the coast. Low pressure also results in a rise
in the mean surface water level. Because the astronomical
tidal range is small along this part of the coast, surges can
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Figure 4. Ground photographs taken in April 2005 of (a) Dunwich Cliffs; (b) Minsmere Cliffs, (c) the high, relatively wide shingle beach ridge barrier
immediately north of Dunwich, and (d) the narrower beach and storm-damaged ridge in the central part of the Dunwich-Walberswick barrier.
have a proportionately large impact on the resultant tidal
levels.
Major surges in 1817, 1883, 1897, 1912, 1928, 1938, 1949,
1953, 1976, and 1978 caused severe damage to flood defences,
agricultural land, and property (C
ORKAN
, 1950; G
ROVE
,
1953; J
ENSEN
, 1953a, 1953b; R
OBINSON
, 1953; R
OSSITER
,
1954; S
TEERS
, 1953; S
TEERS
et al., 1979; S
UMMERS
, 1978).
There are also numerous historical references to major storm
surges in earlier periods (L
AMB
, 1991), although their precise
effects on the coast are poorly documented. The best-docu-
mented surges are those of 1953, 1976, and 1978. According
to S
TEERS
et al., (1979), the surge of 11 January 1978 in-
creased the height of predicted high tide at Southwold by
about 1.0 m, producing a resultant tide level of 2.00 m OD
(Table 1). The surge of 3 January 1976 produced higher re-
sultant levels (2.50 m OD at Southwold). However, the storm
of 31 January 1953 produced the largest surge recorded, and
resulted in the highest high tide levels (3.50 m OD at South-
wold and 3.78 m OD at Aldeburgh). Although no accurate
data exist, the surges of 1938 and 1949 were also severe in
their effects. For example, air photograph evidence suggests
that a large washover fan was created at the northern end of
the RSPB Minsmere Reserve by a breach in the defences dur-
ing the 1938 storm (S
TEERS
, 1951).
Since 1978 the effects of storm surges on the Suffolk coast
have not been particularly severe, partly because of meteo-
rological factors and partly because of improvements in sea
defences (Figures 4 and 5). However, comparison of measured
with predicted tidal levels shows that surges of
,
1 m occur
relatively frequently, and even moderately high resultant
tides can produce significant beach, dune, and cliff erosion
when combined with high waves.
Sediment Sources and Transport Patterns
The general net sediment transport trend along the Suffolk
coast is southwards (M
OTYKA
and B
EVEN
, 1987). Sediment
input to the Dunwich-Sizewell area from the north at the
present day is widely thought to be very small, as is onshore
movement of sediment from deeper water, although strong
evidence is lacking. The most significant input to the near-
shore zone is from coastal cliffs, notably at Pakefield, Bena-
cre, Covehithe, Easton, Dunwich, and Minsmere (Figure 1).
The Dunwich and Minsmere cliffs have a high sand content
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Figure 5. Monthly extreme tidal heights at Lowestoft, 1990–2005 (data
from the National Tide and Sea Level Facility). The heights reached by
the tide at Southwold during the storm surges on 31 January 1953, 3
January 1976, and 11 January 1978, reported by Steers et al. (1979), are
indicated.
(on average
.
90%; B
RITISH
G
EOLOGICAL
S
URVEY
, 1996), al-
though gravel constitutes up to 60% in some areas, and some
glauconitic sand layers contain up to 15% mud. Cliff erosion
and sediment input rates are both spatially and temporally
variable; in recent decades, for example, recession rates of
the Dunwich-Minsmere cliffs have declined compared with
historical rates, and at the present time the cliff faces are
largely stabilised by vegetation (Figures 4a and 4b).
Sand is preferentially transported southwards along the
coast relative to gravel and is ultimately moved offshore.
Ness features at Kessingland, Southwold, and Thorpeness act
as important local sinks for sediments, especially coarser sed-
iments, transported in the intertidal and nearshore zones.
There has been debate whether the nesses also act as sinks
for sediment transported from offshore (R
OBINSON
, 1980), or
are locations from which sediment is transported to the off-
shore zone (C
ARR
, 1981; M
C
C
AVE
, 1978). At Thorpeness,
there is consensus that, although shingle tends to be retained
on the beach, there is a net transfer of sand towards the off-
shore banks. L
EES
(1983) suggested that a tidal residual eddy
may exist off Thorpeness, and may be responsible for trans-
port of sediment towards Sizewell Bank. Computer modelling
(H
ALCROW
M
ARITIME
, 2000b) also demonstrated the poten-
tial for sediment to move offshore from Thorpeness towards
Sizewell-Dunwich Banks during storms, although under av-
erage wave conditions little sediment transport was predict-
ed.
Several attempts have been made to quantify a sediment
budget for the coast between Lowestoft and Thorpeness. V
IN
-
CENT
(1979) and C
LAYTON
,M
C
C
AVE
, and V
INCENT
(1983)
used historical records of cliff recession for the previous 100
years, and measurements of beach volume change from the
1960s and 1970s. H
ALCROW
M
ARITIME
(2000b, 2000c) used
estimated cliff recession rates from short-term beach profile
data and computer modelling to estimate longshore sediment
transport rates. Because these studies relate to different
timescales, the sediment budget estimates vary considerably.
Estimates of sediment input from the Minsmere and Dun-
wich cliffs vary from 40,000 m
3
yr
21
(V
INCENT
, 1979) to
12,000 m
3
yr
21
(H
ALCROW
M
ARITIME
, 2000b, 2000c). V
IN
-
CENT
(1979) estimated the southward net littoral drift of sed-
iment at Dunwich to be 65,000 m
3
yr
21
, whereas H
ALCROW
M
ARITIME
(2000b) calculated a maximum of 12,000 m
3
yr
21
for a shorter, more recent period.
C
ARR
(1981) assessed sediment contributions from cliff ero-
sion and the nearshore zone to the offshore zone over the
period 1867 to 1965, based largely on map evidence. His cal-
culations indicated that erosion of material from the coastal
cliffs is almost balanced by accretion on the Sizewell and
Dunwich Banks. This suggested that the coastline between
Southwold and Thorpeness behaves largely as a closed sys-
tem, with little transfer further to the south. H
ALCROW
M
AR
-
ITIME
(2001a) estimated annual drift to the south of Thor-
peness of 10,000 m
3
yr
21
, which is broadly in agreement with
Carr’s calculations.
CHANGES IN SEA LEVEL AND CLIMATE
Sea Level
Relative sea level in East Anglia was ca. 30 m lower than
present around 9000 years BP (C
OLES
and F
UNNELL
, 1981;
S
HENNAN
and H
ORTON
, 2002). Analysis of sediment cores in
the River Blyth Estuary revealed several transgressive and
regressive phases in the last 9000 years (B
REW
,F
UNNELL
,
and K
REISER
, 1992). Significant regressive periods associated
with peat formation occurred between 6750 and 6500 years
BP and between 4500 and 4300 years BP.
Sea level data for the last 4000 years in Suffolk are sparse.
In northern East Anglia, the average rate of relative sea level
rise since 4000 years BP has been ca. 0.61 mm yr
21
(H
ORTON
et al., 2004; S
HENNAN
and H
ORTON
, 2002), but it is uncertain
whether this is also representative of coastal Suffolk. Data
from the Fenland embayment suggest a slight fall in relative
sea level between ca. 3000 and 2500 years ago, prior to the
Romano-British transgression 2500–2000 years ago (B
REW
et
al., 2000). This was followed by a slight sea level fall and then
a further transgression culminating around 1700–1600 BP.
Sea level may have fallen again between 1400 and 1300 BP,
but was relatively high during the Medieval Warm Epoch
between 900 and 600 BP. Slightly lower sea level is then sug-
gested during the Little Ice Age, which reached maximum
intensity between 1650 and 1750 AD (H
ULME
, 1994). As sug-
gested by L
AMB
(1995), the periods of slightly higher relative
sea level (e.g., 1700–1600 BP and 800–700 BP) may have been
associated with a relative warming of the atmosphere and a
northwards deflection of westerly storm tracks.
Tide gauge data for the Class A station nearest to the Dun-
wich-Sizewell area (Lowestoft) extend back only to 1955. Cy-
clical variations caused by the lunar nodal tidal cycle are ev-
ident, superimposed on an overall upward trend that is par-
ticularly evident since the mid-1970s (Figure 6). The record
indicates a statistically significant rise in mean sea level of
ca. 13 cm over this period. S
HENNAN
and H
ORTON
(2002)
suggested an average relative sea level rise at Lowestoft dur-
ing the 20th century of 1.81
6
0.48 mm yr
21
. However, the
relative contributions of eustatic change, variations in re-
gional tidal range, local land movements, and meteorological
effects to this change remain uncertain.
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Figure 6. Mean monthly and annual sea level recorded at Lowestoft,
1955–2005 (data from Permanent Service for Mean Sea Level).
Wind-Wave Climate and Storminess
Significant variations in weather and climate have affected
the area over the past 2000 years. These have affected sedi-
ment transport patterns, local sediment budgets, and mor-
phological responses. The most marked fluctuations were
during the Medieval Warm Period (1000–1200 AD) and the
Little Ice Age (ca. 1500–1850 AD). Based on an analysis of
long-term measured and proxy weather records, L
AMB
(1995)
proposed that warming phases are associated with an in-
crease in frequency of winds from the southwest, west, and
northwest, and cooling phases with a greater relative impor-
tance of winds from the north and northeast. According to
this model, cooler periods such as the Little Ice Age should
be associated on the Suffolk coast with greater wave energy,
larger and more frequent storm surges, and greater coastal
erosion and flooding. Under such conditions, north to south
sediment drift along the Suffolk coast should be enhanced.
Conversely, during periods of westerly dominance, there
should be less erosion, northerly and southerly sediment
transport should be more in balance, and the coastline should
experience relative stability. During periods of greater storm-
iness and erosion, large amounts of sediment enter the near-
shore zone and are available for redistribution, favouring
southerly spit extension.
A composite record of temperature variation in Central
England extending back to 1659 is available (H
ULME
, 1994;
M
ANLEY
, 1974). This shows that mean annual temperature
was higher than the long-term average (1659–1992) for short
periods in the 18th century (1720–1740) and 19th century
(1820–1830 and 1865–1875) and has consistently been above
the long-term average between 1890 and the present. The
coldest period was between 1640 and 1700. A similar long-
term composite precipitation record for England and Wales
exists for the period 1766–1991. This indicates peaks of wet-
ter periods around 1766, 1790, 1825, 1875, 1925, and 1955,
with drier periods centred around 1775, 1810, 1850, 1890,
1940, 1965, and 1985 (H
ULME
, 1994; W
IGLEY
,L
OUGH
, and
J
ONES
, 1984). Although the relationships between tempera-
ture, precipitation, and wind systems are not simple, there is
a broad association between frequency/duration of westerly
weather types (with dominance of SW, W, and NW winds)
and higher temperatures. Therefore, using this association,
the late seventeenth, late eighteenth, and early nineteenth
centuries were periods when relatively strong north-south
coastal sediment drift along the Suffolk coast could be ex-
pected to have prevailed. Conversely, the last 110 years may
be expected to have been a period of weaker north-south sed-
iment drift, especially after about 1925.
GEOMORPHOLOGICAL CHANGES
Evidence from Historical Maps and
Air Photographs
The earliest map and documentary evidence relating to the
Suffolk coast dates to Saxon times, although the reliability of
the older maps is variable. Despite the deficiencies, it is clear
from such maps and documentary sources that as late as me-
dieval times there were a number of small estuaries open to
the sea near Kessingland, Benacre, Easton, Dunwich, Mins-
mere, and Thorpeness (Figure 1).
A relatively large estuary appears to have existed at Dun-
wich during Roman times, and there is some archaeological
and historical evidence to suggest a Roman settlement or an-
chorage in the area (C
HANT
, 1974; Figure 7). In Saxon times,
following the establishment of a monastery and bishopric,
Dunwich became one of the most important cities in Suffolk.
At this time the Old Dunwich River (or King’s River), whose
remains today flow northwards to join the Blyth near Wal-
berswick, flowed eastwards and possibly formed a common
estuary with the Blyth River, which then flowed southwards,
deflected by a large neck of land (Kingsholme) that extended
south from Southwold.
Although there was considerable erosion of the open coast
between Roman and early Norman times, Dunwich remained
a thriving port, with a population of several thousand and 18
churches, chapels, and monasteries, until the early Middle
Ages (B
ACON
and B
ACON
, 1979, 1984, 1988; C
OMFORT
, 1994).
However, during a storm in 1328 the Dunwich haven became
blocked by shingle, and the River Blyth subsequently forced
a new way through to the sea near Walberswick (S
TEERS
,
1927). Several attempts were made in the following centuries
to form an artificial cut through the shingle near Dunwich,
but all failed, and the town entered a period of progressive
decline. A large part of the medieval town had already been
lost to the sea by 1587, when a detailed map was produced
by A
GAS
(1587), and between 1587 and 1753 further shoreline
recession amounted to approximately 315 m, at an average
rate of ca. 1.9 m yr
21
(R
OBINSON
, 1980; Figure 8). Between
1753 and 1977, ca. 180 m of erosion occurred, at an average
rate of ca. 0.80 m yr
21
. However, the rate of erosion varied
considerably on a decadal time scale. The later 19th and early
20th centuries were evidently a period of faster than average
erosion, with significant land loss and destruction of the for-
mer All Saints Church occurring during this period. Since
1977, the northern Dunwich Cliffs have retreated only a few
metres, and along the southern part of the Dunwich-Walber-
swick barrier the shingle ridge has increased in width (Figure
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Figure 8. Air photograph of Dunwich taken in 2000, showing positions
of the coastline and former churches in 1977, 1753, and 1587. Coastline
positions taken from Agas (1587) and Robinson (1980).
Figure 7. Historical coastline changes in the Southwold-Dunwich area between AD 200 and 1976. Maps are based on reconstructions by Comfort (1994)
and Agas’s map of 1587. The coastline position (base of the cliff or dune) in 1976 is displayed as a solid line on each map for reference. Topography is
shaded at 5 m intervals.
4c). Further north, however, the central and northern parts
of the barrier have experienced erosion and have been main-
tained artificially by periodic bulldozing of shingle from the
beach (Figure 4d). Parts of the barrier have experienced lo-
calised breaching, but so far there has been little net change
in the overall position of the barrier. World War II defences
are still periodically visible on the beach. From Dunwich
southwards towards Minsmere, the beaches have shown net
accretion in the last 10 years, contributing to stabilization of
the cliffs behind (Figures 4a and 4b; P
ONTEE
,P
YE
, and
B
LOTT
, 2004).
Prior to the early Middle Ages, the Minsmere estuary was
a relatively large open water feature. Leiston Abbey was
founded near the shore of the estuary in 1182, and the monks
began building clay embankments to reclaim areas of marsh-
land. However, severe storm flooding in 1347 and 1363
prompted relocation of the Abbey further inland, nearer to
Leiston, leaving only the small chapel on an area of higher
ground near the estuary mouth. The small village of Mins-
mere, which consisted of about 10 houses and a small church,
was also flooded, and was lost to the sea by the 16th century
(B
ACON
and B
ACON
, 1984).
S
AXTON
S
map of 1575 shows that, despite periodic block-
ing by shingle, the havens at Minsmere, Easton, and Kess-
ingland were open to the sea at this time. K
IRBY
S
map of
1737 (Figure 9) shows that the Minsmere River then followed
a very similar course to the present New Cut, flowing slightly
south of east from Eastbridge, and entering the sea just to
the north of the old chapel (at approximately the same posi-
tion as the present sluice). Around this time, laterally contin-
uous shingle barriers began to form along the coast. To the
north, the haven at Benacre was closed to the sea by 1737,
and a large broad, Benacre Broad, was created behind the
new beach barrier. The estuaries at Easton, Minsmere, and
Thorpeness also became blocked in the following decades. At
Minsmere, a shingle barrier had formed by 1752, and this
barrier had completely dammed the estuary by 1780 (A
XELL
and H
OSKING
, 1977). A sluice was initially constructed on the
northern side of the estuary, near to the present Coney Hill,
to allow freshwater drainage.
The low-lying land around Sizewell Belts may have at one
time drained directly to the sea at Sizewell Gap, although
there is no documentary evidence for this. However, H
OD
-
SKINSON
S
map (1783) shows that by 1783 the area drained
northwards, east of the old chapel, into the broad at Mins-
mere. There is no map or geological evidence to indicate that
the Minsmere River ever drained southwards to enter the sea
near Sizewell.
Frequent freshwater flooding in the late 18th and early
19th centuries prompted an Act of Parliament in 1810 to
drain the former estuary, then known as Minsmere Level.
Between 1810 and 1830, a new sluice was created further to
the south, in approximately the same position as the estuary
mouth in 1737. A new drainage ditch was also created, ini-
tially called Huntingsfields Ditch (shown on B
RYANT
S
map
of 1826), and later the New Cut (shown on the First Edition
O
RDNANCE
S
URVEY
map of 1837). A defensive earth bank
was also built between the sluice and the Minsmere end of
the cliffs, at a height of ca. 3 m above the surrounding marsh.
This bank made use of a high area of land at Coney Hill,
which itself was ca. 3 m above the surrounding marsh. A
second bank, running westwards from Coney Hill, was com-
pleted later, between 1883 and 1903. The old river, with its
sluice near Coney Hill, lost its identity between 1826 and
1837, and the Broad was reduced in size by further drainage,
losing its identity by 1890.
Comparison of the 1783 and 1836 maps demonstrates sig-
nificant changes in shoreline orientation north of Minsmere
(Figure 9). In 1783, the coast between Dunwich and Mins-
mere projected some 150 m into the wider bay between
Southwold and Thorpeness. The northern and southern ends
of this promontory coincided with the limits of the Dunwich
and Minsmere cliffs. In the following 50 years, the cliffs ap-
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Figure 9. Historical maps showing coastal changes at Minsmere since 1736, based on maps by Kirby (1737), Hodskinson (1783), and the Ordnance
Survey (1837, 1883–84, 1928, and 1976–82). The position of mean high water in 1976 is displayed as a solid line on each map for reference. Topography
is shaded at 5m intervals.
parently eroded very rapidly, the coastline moving ca. 100 m
landwards. The Minsmere to Sizewell shore also retreated
landwards, albeit at a slower rate than the cliffs, so that by
1836 the promontory had been eroded completely, and a new
slight promontory had been formed in the vicinity of Coney
Hill. Further south, the shoreline had retreated landwards
to align with the northern limit of Sizewell Cliffs at Sizewell
Gap.
The coastal changes since 1836 were quantified by digitis-
ing the positions of mean high water (MHW), mean low water
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Figure 10. Frequency histograms showing changes in (a) the coastline
position, relative to the position in 2003, and (b) foreshore width, mea-
sured along the Environment Agency profile lines shown in Figure 3.
Data are taken from Ordnance Survey maps surveyed in (a) 1836, (b)
1883, (c) 1903, (d) 1920, (e) 1953, and (f) 1976, and (g) from ground sur-
veys by the Environment Agency in 2003.
(MLW) and the ‘‘coastline’’ (defined as the cliff or dune toe,
and approximately equivalent to the position reached by the
highest astronomical tide) from six editions of O
RDNANCE
S
URVEY
maps published in 1837, 1883–84, 1905, 1928, 1958,
and 1976–82, using GIS software. Maps were geo-referenced
using latitude and longitude scales in the map margins,
which were converted to British National Grid (OSGB36) co-
ordinates. The maps were then calibrated with a precision of
ca. 1 metre using six fixed points. It is estimated that this
procedure allowed features on the 1:63,360 map of 1837 to be
digitised with an accuracy of
6
8 m, and features on the 1:
10,560 maps used to be digitised with an accuracy of
6
4m.
The historical positions of MHW, MLW, and the coastline
were then superimposed on the most recent 1:10,000 raster
images of survey data obtained in 1976–82 supplied in digital
format by the O
RDNANCE
S
URVEY
, and compared with
ground survey data obtained by the Environment Agency in
2003. Changes in the position of the coast, and in foreshore
width, between 1836 and 2003, at a number of profile lines
monitored by the Environment Agency since 1991 (see Figure
3), are shown in Figure 10. The former shoreline positions
are also plotted on air photographs of the Minsmere and Si-
zewell areas dating from 2000 (Figures 11a and 11b).
Two phases of coastal evolution between Minsmere and Si-
zewell can be identified after 1836. Between 1836 and 1903
the Minsmere Cliffs retreated rapidly by ca. 156 m, at an
average rate of ca. 2.3 m yr
21
(Figure 10), until the southern
end of the cliffs became aligned with Coney Hill. The Mins-
mere frontage to the north of the sluice also retreated land-
wards, but at a slower rate of ca. 1.1myr
21
. By contrast, the
frontage to the south of the sluice experienced significant ac-
cretion between 1836 and 1903, moving ca. 83 m seawards.
The accretion occurred mostly in the first 50 years, at an
average rate of ca. 1.7 m yr
21
. The historical position of the
coastline in 1836 is represented on the ground by a secondary
dune ridge, lying behind the present line of frontal dunes.
The sluice acted as an anchor point, separating an area of
net erosion in the north from an area of net accretion in the
south, with no change in the position of the coastline. The
sluice has, in effect, acted as a fulcrum for an anticlockwise
movement of the coastline.
Between 1903 and 1976, the rate of coastal change declined
significantly. Very little change occurred south of the sluice,
the position of the coast being defined by the development of
a dune ridge by 1903. The shore between the sluice and Co-
ney Hill experienced some accretion after 1903, moving ca.
20 m seawards, because of the development of a vegetated
shingle ridge and low foredune ridge behind. Minsmere and
Dunwich Cliffs continued to erode, at an average rate of ca.
1.3 m yr
21
in the 50 years between 1903 and 1953 and ca.
0.6 m yr
21
between 1953 and 2003. As the Minsmere and
Dunwich cliffs retreated, the coastline between Coney Hill
and the end of the cliffs has also retreated, the low foredune
dune ridge migrating landwards by 20–30 m (Figure 11a).
Air photographs of the Minsmere area taken in July 1940
show evidence of erosion and flooding following a severe
storm event, probably associated with the 1938 storm surge.
To the north of Coney Hill, much of the dune ridge had ap-
parently been eroded or flattened, with vegetation being re-
moved back to the clay bank. At Coney Hill, the sea had also
breached the bank, with a large washover fan spread over
the marsh. To the south of Coney Hill, although the dune
ridge appears to have been eroded on its seaward side, it
remained quite well vegetated, and was apparently not
breached. South of the sluice, where the dunes were higher,
erosion appears to have been localised, and the coast fronting
what is now Sizewell Power Station showed no significant
erosion.
In common with other strategically vulnerable areas, the
Minsmere Levels were flooded in June 1940 as a defensive
measure against possible German invasion during the Second
World War. A radar station, lookout post, and gun battery
were established at the southern end of Minsmere cliffs (N
A
-
TIONAL
T
RUST
, 2004). Aerial photographs taken in July of
that year clearly show the flooded areas. In addition to flood-
ing, concrete blocks were placed along the backshore and oth-
er anti-invasion hardware was installed on the beach. The
sluice remained open until the end of hostilities in 1945.
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Figure 11. Air photographs taken in 2000 of (a) the northern end of the Minsmere Cliffs–Minsmere Sluice frontage and (b) the MinsmereSluice–Sizewell
frontage, showing superimposed historical coastline positions.
Air photographs taken in 1952 show that the coast south
of Coney Hill had recovered well from the 1938 storm, and
that the dune ridge was then well vegetated. A ground pho-
tograph taken in 1950 (S
TEERS
, 1960) shows that the dune
ridge was still relatively low at this time. The beach was ev-
idently quite sandy, which would have aided accretion of the
dunes. To the north of Coney Hill, the backshore does not
appear to have recovered well. Photographs show little evi-
dence of dune ridge formation, and an artificial clay bank
provided the only effective flood defence. The washover fan
at Coney Hill was unvegetated and appeared to have been
recently active, possibly as a result of the 1949 storm surge.
Although photographic evidence is not available, the storm
surge of 31 January–1 February 1953 probably caused addi-
tional erosion to the north of Coney Hill, reactivating the
washover fan and removing any newly formed dunes. Follow-
ing the 1953 storm, the backshore north of Coney Hill, in
front of the artificial bank, was planted with vegetation to
encourage dune growth and to protect the marsh behind. Air
photographs show that by 1968 a vegetated shingle ridge had
developed to the north of Coney Hill, whereas south of Coney
Hill a new dune ridge, seaward of the original, had begun to
form. Some vegetation had also become established on the
washover fan north of Coney Hill.
Air photographs taken in 1991 show continued widening of
the dune ridges and increasing vegetation cover between Co-
ney Hill and the sluice. The line of concrete blocks, laid at
the back of the beach in 1940, was by this time located sev-
eral metres back from the beach. Some further accretion is
apparent to the south of the sluice, although there was con-
siderable disturbance to the beach and frontal dunes associ-
ated with the building of the Sizewell B Power Station.
Since 1976, the dune ridge along the northern end of the
Minsmere Reserve has retreated approximately 5 m inland
(Figure 11a). South of the sluice, there was further accretion
between 1976 and the early 1990s, since which time part of
the dune frontage has started to erode (Figure 12d). Recent
field surveys suggest that most of the shoreline is now rela-
tively stable, although the area north of Sizewell Power Sta-
tion is still experiencing periodic storm erosion. This may be
related to changes in the nearshore and offshore morphology,
including the development of a gap between the crests of the
Sizewell and Dunwich Banks through which waves are able
to penetrate. The northern part of the Minsmere barrier just
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Figure 12. Ground photographs taken in November 2004 showing (a) view from Minsmere cliffs toward Sizewell, (b) wave-eroded frontal dune ridge at
the northern end of the Minsmere RSPB Reserve frontage, (c) view of the ‘‘Scrape’’ lagoon behind the central part of the Minsmere barrier, and (d) wave-
eroded frontal dunes between Minsmere sluice and Sizewell Power Station.
south of Minsmere Cliffs has suffered most from recent fron-
tal dune erosion and localised overtopping when tidal levels
exceed 2.0 m OD, because of the low, narrow nature of the
upper beach and dune ridge in this area. However, the pre-
sent position of the shoreline in this area is not very different
from its position in the early 1940s.
Evidence from Bathymetric Charts
Approximately 20 Admiralty Charts dating from 1868 to
2004, were examined in order to assess changes in the ba-
thymetry between Southwold and Thorpeness. Although new
editions of Admiralty Charts are published almost annually,
charts usually include data from several surveys conducted
at different times, sometimes decades apart. After an initial
survey in 1845, the seabed remained largely unsurveyed for
the next 100 years, except for Sizewell Bank, which was im-
portant for navigation purposes. The next major resurveys
were conducted around 1940 and 1960.
Six charts, dating from 1868, 1908, 1940, 1960, 1974 and
1992, were selected and digitised. These charts were pub-
lished after major resurveys, and although each contains
data spanning a number of years, they provide the best avail-
able indication of the situation at the given dates. However,
in using any Admiralty charts for sediment volume change
calculations it is important to recognise that potential errors
may arise because of variations in survey methods and
changes in datum levels used in different surveys (V
AN
D
ER
W
AL
and P
YE
, 2003).
In 1868, there were two distinctly separate banks, Dun-
wich Bank in the north, and Sizewell Bank in the south (Fig-
ure 13). Sizewell Bank was by far the largest and most im-
portant. The bank had a teardrop shape, the highest part
being ca. 3 m below Chart Datum, with a slender ridge ex-
tending ca. 7 km to the north. The bank had an amplitude of
ca. 8 m above the surrounding seabed and ran subparallel to
the coast. Dunwich Bank was much smaller (c.1.5 km in
length). It had an amplitude of only 3 m above the surround-
ing seabed, with the highest point some 7 m below Chart
Datum. The bank also lay ca. 2 km from the shore, near Dun-
wich. To landward of the Sizewell-Dunwich Bank, the 1868
chart shows a bar and trough running parallel to the coast
some 300 m from the shore. The main trough had a depth of
ca. 2 m, and extended from Dunwich to Sizewell.
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Figure 13. Changes in the position and shape of the Sizewell-Dunwich
Banks between 1868 and 1992, based on Admiralty surveys.
Analysis of detailed changes between 1868 and 1940 is not
possible because of the lack of survey information. The 1908
chart shows only that the southern part of Sizewell Bank had
moved towards the coast since 1868, although it does not ap-
pear to have accreted vertically. Subsequent charts in 1918
and 1922 show that the southern part of Sizewell Bank
moved towards the north and east. The area to the south of
the bank, offshore from Thorpeness, also accreted, the bank
rising to just 2 m below chart datum. The foreshore at Thor-
peness also experienced significant accretion.
A survey in the late 1930s provided the first update on
changes to the north of Sizewell since 1868. Changes in the
intervening period had been significant. By 1940, Dunwich
Bank had merged with the northern part of Sizewell Bank to
produce one long bank running subparallel to the coast from
Dunwich to Thorpeness, approximately 2 km from the shore
(Figure 13). The crest of the bank generally lay 4–5 m below
Chart Datum, with an amplitude of 5–6 m above the sur-
rounding seabed (Figure 14). The highest part of the bank
was still located nearest to Sizewell, and this had migrated
about 700 m closer to the shore. As proposed by R
OBINSON
(1980), the increase in height of the bank offshore from Dun-
wich would probably have reduced storm wave activity along
this part of the coast, and may well have contributed signif-
icantly to the observed reduction in cliff erosion rates after
this time.
The chart of 1960 still showed a continuous ridge extending
from Dunwich to Thorpeness, although a low point in the
ridge had formed just to the south of the sluice at Minsmere,
and Dunwich and Sizewell Banks could once again be rec-
ognised as separate features. The ridge also showed signs of
erosion since 1940, with a narrower, more sinuous morphol-
ogy. Sizewell Bank was still the highest part of the ridge,
although its crest had been lowered to ca. 4 m below Chart
Datum. Dunwich Bank had also been lowered, and had mi-
grated ca. 800 m landwards between 1940 and 1960. Con-
versely, the area to the east of the banks had accreted, the
2
15 m OD contour moving about 250 m offshore. Overall,
the bank system appears to have been lowered, but had also
spread out to cover a wider area. When survey errors are
allowed for, these changes remain significant.
Between 1960 and 1974, erosion apparently continued,
with a deepening of the low point between the two banks,
south of Minsmere sluice. The crests of the banks were still
3–4 m below Chart Datum, and had not migrated landwards
since 1960, although they had both narrowed. The seabed
landward of these banks along the Minsmere frontage had
also deepened to ca. 11 m below Chart Datum. Deepening in
this area may partly have been a consequence of reduced cliff
erosion, with less sediment being introduced to the coast and
nearshore zone. To the east of the banks, continued accretion
in deeper water had caused the
2
15 m OD contour to migrate
a further 500 m offshore.
Erosion of the banks apparently continued through the
1980s, as the chart of 1992 shows both Dunwich and Sizewell
Banks shrinking further in size, although largely maintain-
ing their crest height. The banks had also migrated a further
200 m inshore. By 1992 the ‘‘trough’’ at Minsmere, landward
of the banks, had infilled slightly, although depths in excess
of 10 m were recorded less than 1 km offshore from Minsmere
Sluice. Little change has been recorded in charts published
since 1992, only the frontage between Minsmere and Thor-
peness having been resurveyed. During this period Sizewell
Bank appears to have maintained its lateral and vertical ex-
tent. The deep area landwards of the banks has infilled
slightly, although depths of up to 10 m are still recorded near
Minsmere. At Sizewell, local changes in the beach and near-
shore morphology have undoubtedly been influenced in the
last 30–40 years by construction of piers, water intakes, and
discharge pipes associated with the power stations. The net
effect of these works appears to have been to encourage in-
tertidal and shallow subtidal sediment accumulation in this
area.
Sediment volumes across a defined area of the Dunwich
and Sizewell Banks were calculated for each Admiralty chart
(Table 2; Figure 14). Sediment volume calculations for the
2
5to
2
10 m depth interval illustrate the main changes on
the banks, and show that the greatest changes occurred be-
fore 1960, when the banks increased in volume by ca. 18%.
The banks then lost sediment volume over the following de-
cades. Sediment volume changes above
2
30 m depth indicate
that the greatest changes also occurred between 1940 and
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Figure 14. Bathymetric changes along alternate shore-normal transects (a) up to 12 km offshore between 1868 and 1992, based on Admiralty charts,
and (b) up to 3 km offshore, based on Environment Agency bathymetric surveys during the summers of 1992, 1997, and 2003. The positions of the
transect lines are shown on Figure 3.
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Table 2. Sediment volume changes across Sizewell and Dunwich Banks determined by analysis of historical Admiralty charts. Calculations were made for the area between 262000N and 272000N,
and 646000E and 652000E (British National Grid coordinates).
Datum
(m CD)
Volume Above Datum (10
6
m
3
)
1868 1908 1940 1960 1974 1992
Volume Change Above Datum (%)
1868–1908 1908–1940 1940–1960 1960–1974 1974–1992 1868–1992
2
5
2
10
2
15
2
20
2
25
2
30
13.1
98.5
281.2
482.8
691.8
900.9
14.5
101.6
284.1
485.6
694.5
903.5
14.4
109.8
286.7
486.2
693.7
901.3
18.2
121.3
306.8
512.3
723.0
933.8
15.7
118.4
304.6
512.6
722.7
932.8
14.0
106.1
292.8
501.8
711.6
921.3
11.1
3.2
1.0
0.6
0.4
0.3
2
1.1
8.1
0.9
0.1
2
0.1
2
0.2
26.9
10.4
7.0
5.4
4.2
3.6
2
14.0
2
2.4
2
0.7
0.1
0.0
2
0.1
2
10.6
2
10.3
2
3.9
2
2.1
2
1.5
2
1.2
7.1
7.8
4.1
3.9
2.9
2.3
Volume Change Between Datums (10
6
m
3
) Volume Change Between Datums (%)
2
5to
2
10
2
10 to
2
15
2
15 to
2
20
2
20 to
2
25
2
25 to
2
30
85.4
182.7
201.6
209.0
209.1
87.1
182.5
201.5
208.9
209.0
95.5
176.8
199.5
207.5
207.6
103.1
185.5
205.6
210.7
210.7
102.7
186.2
208.0
210.1
210.2
92.1
186.7
209.0
209.8
209.8
2.0
2
0.1
0.0
2
0.1
2
0.1
9.6
2
3.1
2
1.0
2
0.6
2
0.7
8.0
4.9
3.0
1.5
1.5
2
0.3
0.4
1.2
2
0.3
2
0.3
2
10.3
0.3
0.5
2
0.2
2
0.2
7.9
2.2
3.7
0.4
0.3
1960, when the area to the east of the banks accreted and
the
2
15 m OD isobath migrated offshore. In part this may
reflect redistribution of sediment during and following the
major storm surges of 1938, 1949, and 1953. This offshore
area subsequently lost sediment between 1974 and 1992. The
net change between 1868 and 1992 was apparent accretion
of 20.5 km
3
of sediment, representing an increase of 2.3%, a
figure that is within the range of potential error that could
arise from survey and data analysis methods.
Assuming an average recession rate of 1.49 m yr
21
for the
Minsmere and Dunwich Cliffs, and an average cliff height of
10 m and cliff length of 3 km, it can be estimated that be-
tween 1868 and 1992 the cliffs supplied ca. 5.5 km
3
of sedi-
ment to the nearshore zone. Over this same period, the coast
to the north of Coney Hill also eroded, supplying an addition-
al ca. 0.2 km
3
of sediment, whereas the coast to the south of
Minsmere experienced accretion, amounting to ca. 0.7 km
3
of
sediment. The total figure is considerably less (representing
ca. 25%) than the apparent increase in sediment volume of
20.5 km
3
observed on the Dunwich-Sizewell Banks. If addi-
tional sediment had indeed accumulated on the banks and
adjacent offshore areas, it must have been derived from fur-
ther north, including the cliffs at Easton, Covehithe or Pak-
efield, or from offshore.
Evidence from Beach and Bathymetric Profile Data
Since 1991, the Environment Agency Anglian Region has
surveyed beach profiles along transects (some of which are
shown on Figure 3) spaced at approximately 1 km intervals
as part of a Strategic Monitoring Programme. Beach surveys
are carried out annually to low water, in both winter and
summer. Bathymetric surveys are also undertaken nominally
every 5 years to a distance of ca. 3 km offshore. Combined
beach and offshore bathymetry profiles relating to four of the
transects between Dunwich and Sizewell for the years 1992,
1997, and 2003 are shown in Figure 14. Data for the two most
northerly profiles indicate that the trend of lowering and
landward migration of Dunwich Bank, identified from histor-
ical charts, has continued in recent years. Between 1992 and
2003, the crest of Dunwich Bank dropped ca. 1 m in elevation,
and migrated landward by 100–200 m. The area to the west
of the bank, however, increased in elevation by ca. 1 m as a
result of infilling by sediment. Further south, profiles S1B1–
S1B5 also show a landward migration of the banks by 100–
200 m, and a depth reduction of 0.5–1.0 m in the trough land-
ward of the banks. There was, however, no net change in the
level of the bank crest. Changes on the southernmost profile,
S1B6, show that the position of Sizewell Bank was stable
between 1992 and 2003, with no net change in the level of
the crest of the bank, although there was significant sedi-
ment accretion in the area landward of the bank.
At all profiles, changes in the beach down to the level of
Lowest Astronomical Tide (
2
1.6 m OD), were relatively
small. All profiles show some reduction in beach volumes be-
tween 1992 and 2003 except profile S1B3, located immedi-
ately to the south of the sluice, which accreted slightly. How-
ever, the fluctuation in beach volumes from year to year is
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Figure 15. Map showing parts of the Minsmere Reserve that could po-
tentially be flooded by a tide equivalent in height to the present Highest
Astronomical Tide, following possible storm breaching of the dune de-
fences (based on the 1999 LIDAR survey).
Figure 16. Maximum crest height of the frontal dune ridge between Sizewell and Minsmere Cliffs, extracted from a LIDAR survey in 1999.
greater than the net erosion or accretion taken over the 11-
year period.
Considering the entire profile lengths, down to ca.
2
12 m
OD, all profiles accreted between 1992 and 2003 by between
7% and 10%, with the exception of S1B1, to the north of Co-
ney Hill, which accreted by less than 5%.
Evidence from LIDAR Data
Data from a LIDAR survey flown by the Environment
Agency in March 1999 were analyzed to derive a digital ele-
vation model (DEM) of the area between Minsmere Cliffs and
Sizewell. Ground survey data provided by the RSPB were
used to estimate the vertical accuracy of the LIDAR data by
comparison with recorded elevations at known grid referenc-
es. This showed that the LIDAR generally underestimates
the height of banks and sea walls by ca. 0.3–0.6 m, because
the horizontal resolution of the LIDAR data (2 m) is similar
to the width of the top of the banks. Conversely, the LIDAR
generally overestimates the elevation of low-lying ground be-
tween the banks and sea walls because of reflections from
the vegetation. The overestimation is greatest for the reed-
beds, the LIDAR data being ca. 0.5–0.7 m higher than the
ground survey data. Differences are smaller for the grassland
areas, where the LIDAR height values are ca. 0.1–0.3 m high-
er than the ground survey values.
The LIDAR DEM showed that large areas of land behind
the coastal defences are low-lying and vulnerable to flooding
in the event of a major breach. Much of the land across Mins-
mere Level and Leiston Marsh, extending up to 3 km inland,
lies between 0.6 and 0.7 m OD. Areas to the north of the
Minsmere Old River and Coney Hill are slightly higher, at
ca. 1.5 m OD. These areas drain onto Minsmere Level by
gravity flow. Figure 15 shows that a large area of land would
potentially be flooded by a tide level equivalent to present
Highest Astronomical Tide if the Minsmere barrier was
breached.
The dune ridge fronting Sizewell Power Station is gener-
ally higher than 5 m OD, although there is one section where
the dune crest drops below 5 m OD (Figure 16). However,
there is currently no direct flood risk to the power station,
which is constructed on higher ground. Between the power
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station and Minsmere sluice, the frontal dune ridge is wide
and high (
.
6 m OD), and for much of this length is backed
by the earlier dune ridge. For a distance of 700 m north of
the sluice, the ridge is narrower and lower, with a crest
height of 4.5–5.0 m OD. The dunes along this section are,
however, fairly wide and well vegetated. The ridge between
this point and Coney Hill is lower (4.0–4.5 m OD), although
this section is backed by a second dune ridge. North of Coney
Hill, the dune ridge is both low and narrow. In places, the
crest lies below 4 m OD, including an area where overtopping
occurred during a storm on 14–15 December 2003. This 200-
m-long section represents the most likely location for a major
breach during a future storm surge. However, the primary
dune defence is backed by a secondary defence line (clay
bank), and the North Marsh area is separated from the main
freshwater reedbed in the RSPB Reserve by a further sea
bank (the North Wall). Widespread flooding of The Scrape
(Figure 12c) and main reedbed areas is therefore unlikely to
occur in the near future as a result of breaching at the ex-
treme northern end of the site.
FUTURE MANAGEMENT OPTIONS
In June 2004 the Environment Agency published a draft
consultation document outlining the options for future flood
risk management on the Minsmere to Sizewell section of the
coast (E
NVIRONMENT
A
GENCY
, 2004). The options listed were
as follows:
(1) Do Nothing or No Active Intervention
(2) Do Minimum
(3) Hold the Line
(a) Beach recharge
(b) Offshore breakwaters
(c) Rock armour groynes
(4) Managed Realignment
(a) Frontage realignment
(b) Mid-realignment
(c) Extensive realignment
The ‘‘Do Nothing or No Active Intervention’’ option would
involve cessation of all maintenance, repair, and renewal
work to the Minsmere sluice, embankments, frontal dune and
beach. Under this option, continued erosion of the northern
part of the Minsmere frontage between Minsmere Cliffs and
Coney Hill would be expected. Washovers or breaches of the
dune ridge would not be repaired, leading to possible further
overtopping of the dune ridge at these locations during sub-
sequent high tides. Ultimately, erosion of the clay embank-
ment behind the dune ridge could lead to tidal inundation of
the freshwater habitats on the Minsmere Reserve. Such a
breach could occur at any time if the coast were to experience
another surge approaching 1953 proportions. However, there
is no certainty regarding when and if such a major storm will
occur, and this section of shore could continue to exist in a
state of dynamic equilibrium, similar to that which has ex-
isted since 1953, for a further 50 years. However, when con-
sidering a time frame beyond the next 20 years, the uncer-
tainties relating to possible accelerations in sea level rise and
increased storminess increase significantly.
A strict ‘‘Do Nothing’’ policy would, as sea level rise contin-
ues even at present rates, ultimately result in nonfunctioning
of the gravity-driven drainage system on the Minsmere Lev-
els. In order to prevent increased risk of prolonged freshwater
flooding in this area, improvements to the present sluice, in-
cluding a pumped drainage system, would need to be made
in the next 10–20 years.
The ‘‘Do Minimum’’ option allows for repair of the defences
if damage occurs, and minor preventative works, but does not
provide for major routine maintenance of the defences or im-
provement of the standard of defence. The implications of
such a strategy for the Minsmere frontage are that any minor
works undertaken are unlikely to have any significant impact
on the direction of the average medium-term rate of coastal
change. The Coney Hill to Minsmere cliffs frontage will con-
tinue to be vulnerable, as under the ‘‘Do Nothing’’ approach,
but in the absence of a very major storm surge the likelihood
of a major breach will be reduced to some extent. In essence
this is the policy that is currently in operation, minor repair
works (involving redistribution of shingle along the beach,
reprofiling by bulldozing, placing of faggots, etc.) having been
undertaken before and following recent winter storm events.
The ‘‘Hold the Line’’ option involves maintaining or im-
proving the standard of coastal defence. Three options for
‘‘holding the line’’ have been identified: offshore breakwaters,
rock armour groynes, and beach recharge. These options
could be implemented in conjunction with other measures,
such as a partial realignment of defences for part of the site,
or changes to the tidal sluice. A strict ‘‘Hold the Line’’ policy
is unlikely to be sustainable for the Minsmere Reserve front-
age in isolation, because recession of the cliffs to the north
will continue if they are not protected, and this will place
erosion pressure on the Minsmere shoreline. Any scheme re-
lating to Minsmere would necessarily have to involve the en-
tire coastal zone extending at least from Southwold to Thor-
peness.
Groynes and rock armour would almost certainly be re-
garded as environmentally unacceptable under present cir-
cumstances, in terms of both their impact on aesthetic envi-
ronmental quality and their disruptive effect on natural
coastal processes.
Offshore breakwaters constructed parallel to the shore
would reduce wave energy and probably reduce net sediment
erosion rates from the beach/inner nearshore zone. However,
breakwaters could have a major impact on sediment trans-
port processes and would not allow any natural adjustments
in the alignment of the coast. Rock breakwaters would have
the added detrimental effect on landscape quality. However,
if in the future erosion and flood risk were to significantly
increase, especially to the Sizewell Power Station complex,
‘‘firm’’ engineering measures such as rock breakwaters,
groynes and, rock armour revetment might be justified, at
least locally.
Beach nourishment is widely regarded as a more environ-
mentally friendly ‘‘soft’’ engineering option, and has been suc-
cessfully used in several other parts of the UK, including the
East Coast (e.g., B
LOTT
and P
YE
, 2004). By an increase in the
beach volume, width, and height, capacity to dissipate wave
energy would be enhanced. Provided that the recharge ma-
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terial had a suitable particle size distribution, aeolian trans-
port would be enhanced, thereby increasing the width and
height of the back-beach dune ridge. However, a scheme of
this type would need to involve the entire section of coast
from Dunwich to Thorpeness. A proportion of the sandy sed-
iment would be moved southwards along the coast towards
Thorpeness, and then offshore to the Sizewell-Dunwich
Banks, creating a periodic requirement for renourishment.
However, because sediment net transport rates are relatively
low along this section of coast, losses of nourishment mate-
rial, especially the coarser gravel fraction, would not be ex-
pected to be rapid. The principal issues relating to such a
scheme would therefore relate to sourcing of the material,
cost, and possible environmental impacts both in the source
and nourishment areas.
‘‘Managed Realignment’’ would require identification of a
preferred landward line of defence and a plan for a (possibly
staged) retreat of the shoreline. Three possible options for
realignment have so far been identified by the Environment
Agency. All would involve the loss of part or all of the Mins-
mere Reserve in its present form. Any loss of habitat caused
by realignment of sea defences would require compensation
in the form of replacement habitat elsewhere. Even if it were
possible to recreate comparable habitat elsewhere, this would
involve a considerable economic cost to the Agency, and could
indirectly affect the local economy of the area through loss of
visitors.
‘‘Frontage realignment’’ would involve relocating the pre-
sent first line of defence ca. 150 m inland along the whole
coastline between Minsmere Cliffs and Sizewell. This defence
line would encroach into the Minsmere Reserve with some
loss of freshwater habitats. This option would allow the coast-
line at the northern end of the Minsmere frontage to retreat
in sympathy with the cliffs. The key to the success of such a
scheme would be the position of the Minsmere sluice. In the
Environment Agency plan, the position of the outfall would
be maintained, although the implementation of an additional
sluice or replacement with a pumping station would be con-
sidered. Evidence from historical maps has shown that the
sluice has acted as an anchor point to the coastline. A front-
age realignment would therefore require a landward move-
ment of the sluice to maintain the alignment with the coast-
line to the north. This would also require the landward move-
ment of the outfall, because in its present position it would
act as a sediment groyne restricting longshore drift along the
newly aligned coast. Although this scheme would benefit the
coastline to the north of the sluice, by realigning the shore
with the cliffs, the coast to the south of the sluice could ex-
perience erosion. Historical evidence has shown that accre-
tion along this part of the coast was only possible because of
the present location of the sluice. Removal or ‘‘setback’’ of this
part of the shore-dune system would also have a potentially
serious effect on the Sizewell defences. It is therefore impor-
tant to consider how such a realignment would be imple-
mented. Although some areas could be allowed to retreat, or
‘‘roll back,’’ to the new defence line naturally, the sluice and
outfall would require active setback. In the short term, this
could result in substantial erosion and southward transport
of sediment before the defences could roll back to the new
line. In this way, a large volume of sediment in the dune
ridges could be lost rather than forming a new line of defence.
‘‘Mid-realignment’’ or ‘‘extensive realignment’’ would both
involve relocating the line of defence to the higher ground
that surrounds the Minsmere Reserve (1.4–2.6 km inland).
Flood barriers would be required at the landward limit to
protect assets upstream. Both these options would result in
the loss of many of the current habitats on the Minsmere
Reserve, including fresh and brackish water pools, freshwa-
ter reedbed, and grazing marsh habitats. There would also
be a substantial economic cost because of the loss of these
habitats (in terms of compensation). These options would be
expensive, requiring the construction of flood barriers and
sluices to protect areas to the west and south of the new tidal
area, including Sizewell Belts.
There is a view that maintenance of the existing freshwater
habitats at Minsmere is not a sustainable option, and the
long-term (
.
100 years) outlook for the area must involve its
conversion from freshwater to saline water habitats. Accord-
ing to this view, it would be sensible to employ a short- to
medium-term strategy to warp up the Minsmere wetland by
permitting inundations through the sluice, as a precursor to
a full scale transition to tidal habitat. This is based on the
fact that the surface elevation of the wetland is now 1–2 m
lower than MHW, and that in 100 years there will be a short-
age of fine sediment availability, which may prevent devel-
opment of intertidal habitat. However, uncertainty surrounds
the impact of restoring the Minsmere tidal estuary. Although
it may be hypothesized that reopening or removing the Mins-
mere tidal sluice would lead to the reformation of an ebb tidal
delta, which would reduce water depths and aid wave dissi-
pation along the Minsmere to Sizewell shoreline, no detailed
assessment of the possible effects has been undertaken.
CONCLUSIONS
The Dunwich-Sizewell coast has experienced significant
erosion and shoreline recession in historical times, but there
is no evidence that rates of coastal recession and/or frequency
of flooding have accelerated in recent decades as a result of
sea level rise, increased storminess, or any other factor. In-
deed, the evidence indicates that the opposite has occurred.
Relatively little change in shoreline position has occurred
since the Second World War. However, this situation could
change in the future if predictions about increases in the rate
of sea level rise and storminess prove correct. The effects of
such changes might not be significant for at least 30–50
years.
At present there is little scientific evidence to support a
case for a large-scale realignment of the defences along the
coast between Dunwich and Sizewell, or for a reopening of
the former Minsmere River estuary to tidal influence. Apart
from some local recent cliffing of the frontal dunes south of
Minsmere Cliffs and to the north of Sizewell Power Station,
the shoreline has moved very little in the past 50 years, and
over a longer timescale the coast south of the sluice has pro-
graded substantially. Rates of cliff erosion at Dunwich, and
shoreline recession at the northern end of the Minsmere Re-
serve, have actually declined in the past 50 years. The beach
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and frontal dunes at the northern end of the Minsmere Re-
serve frontage are at present aligned slightly too far seaward
with respect to the rest of the shoreline, and consequently
there is erosion and a risk of wave overtopping in this area.
However, in the absence of a major storm event of 1953 pro-
portions the risk of a major breakthrough, leading to exten-
sive flooding of the Minsmere Reserve, is low.
Further north, the middle and northern parts of the arti-
ficially-maintained Dunwich-Walberswick barrier are clearly
out of alignment with regard to current coastal processes and
the local sediment regime. The barrier has been very suscep-
tible to erosion, with localised breaching and overtopping, in
recent years, and there is a high risk of a major breach and
possible flooding of the Dingle Marshes under severe storm
conditions. Consequently, unless a major beach nourishment
scheme is undertaken, landward repositioning of the main
ridge, combined with further strengthening of the secondary
flood defences (earth embankments) will be required in the
very near future.
ACKNOWLEDGEMENTS
Provision of LIDAR data, topographic data, bathymetric
profile data, and air photographs by The Environment Agen-
cy Anglian Region, and the RSPB is gratefully acknowledged.
Particular thanks are due to David Welsh (Environment
Agency Anglian Region) and Helen Deavin (RSPB Norwich
Office) for assistance with data provision and helpful discus-
sion.
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The project was conceived primarily as a regional study of an offshore bank and its relationship with shoreline equilibrium. Subsequently the programme evolved to its present wider concept, part of which examines the interrelation between coastline and offshore in general. More importantly it has, together with the Swansea Bay (Sker) Project, become an in-depth study of nearshore large scale processes of sediment transport under waves and tidal currents. (A)