Earth Surface Processes and Landforms
UK
habitatLandforms
future 31, 1625–1642 (2006)
Earthcoastal
Surf. Process.
Published online in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/esp.1429
1625
Challenging assumptions of future coastal habitat
development around the UK
Julian D. Orford1* and John Pethick2
1
2
School of Geography, Archaeology and Palaeoecology, Queen’s University, Belfast, BT7 1NN, UK
Beverley, East Yorkshire, HU17 0DN, UK
*Correspondence to: J. D. Orford,
School of Geography, Archaeology
and Palaeoecology, Queen’s
University, Belfast, BT7 1NN,
UK. E-mail: [email protected]
Received 1 February 2005;
Revised 4 November 2005;
Accepted 20 December 2005
Abstract
One habitat management requirement forced by 21st century relative sea-level rise (RSLR),
will be the need to re-comprehend the dimensions of long-term transgressive behaviour of
coastal systems being forced by such RSLR. Fresh approaches to the conceptual modelling
and subsequent implementation of new coastal and peri-marine habitats will be required.
There is concern that existing approaches to forecasting coastal systems development (and
by implication their associated scarce coastal habitats) over the next century depend on a
certain premise of orderly spatial succession of habitats. This assumption is shown to be
questionable given the possible future rates of RSLR, magnitude of shoreline retreat and the
lack of coastal sediment to maintain the protective morphologies to low-energy coastal habitats. Of these issues, sediment deficiency is regarded as one of the major problem for future
habitat development. Examples of contemporary behaviour of UK coasts show evidence of
coastal sediment starvation resulting from relatively stable RSLR, anthropogenic sealing of
coastal sources, and intercepted coastal sediment pathways, which together force segmentation of coastal systems. From theses examples key principles are deduced which may prejudice the existence of future habitats: accelerated future sediment demand due to RSLR may
not be met by supply and, if short- to medium-term hold-the-line policies predominate, longterm strategies for managed realignment and habitat enhancement may prove impossible
goals. Methods of contemporary sediment husbandry may help sustain some habitats in
place but otherwise, instead of integrated coastal organization, managers may need to consider coastal breakdown, segmentation and habitat reduction as the basis of 21st century
coastal evolution and planning. Copyright © 2006 John Wiley & Sons, Ltd.
Keywords: UK coastal habitats; habitat assumptions; sea-level rise rates; shoreline realignment; sediment deficiency; sediment husbandry; coastal segmentation
Introduction
The enormous challenges presented to coastal habitat development and maintenance through the environmental changes
potentially forced by the acceleration of global climate change in the coming century are, by now, well known. Yet,
although there is a common perspective on the idea of such change in the coastal community, there is little unanimity
as to its scale, the dominant dimensions of change to come, or future actions required to work towards sustainable
development of natural habitats in the coastal zone. This paper is an attempt to stimulate debate on some of the
underlying assumptions that are perceived to control present approaches to these challenges and also to question
assumptions about the nature of future coastal habitats.
Over the last two decades in the UK, detailed consideration has been given to future forcing (Hulme et al., 2002;
Evans et al., 2004) and the future evolution of the coastlines of England and Wales (Burgess et al., 2002). ‘Uncertainty’ is a major component of all of these studies, yet despite the readjustment of expectations of the human
response to coastal change as witnessed by the evolution of the second generation of Shoreline Management Planning
(Defra, 2001), there seems to be a lack of any similar critical examination of likely future habitat responses to physical
shoreline changes. There has been a limited attempt to consider the future evolution of coastal habitats under climate
change (CHAMPS programme: English Nature, 2004), but these relate to specific locations where current designations
Copyright © 2006 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms 31, 1625–1642 (2006)
DOI: 10.1002/esp
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J. D. Orford and J. Pethick
Table I. EU Strategic coastal habitats and the UK’s individual coastal habitat responsibilities identified under the Natura (2000)
programme
Code
Current name as adopted in Directive 97/62/EC
1130
1140
1150
1160
1170
1210
1220
1230
1310
1320
1330
2110
2120
2130
2140
2150
2160
2170
2190
21A0
2250
Estuaries
Mudflats and sandflats not covered by seawater at low tide
Coastal lagoons
Large shallow inlets and bays
Reefs
Annual vegetation of drift lines
Perennial vegetation of stony (shingle) banks
Vegetated sea cliffs of the Atlantic coasts
Salicornia and other annuals colonizing mud and sand
Spartina swards (Spartinion maritimae)
Atlantic salt meadows (Glauco-Puccinellietalia maritimae)
Embryonic dunes
Shifting dunes along the shoreline with Ammophila arenaria (‘white dunes’)
Fixed dunes with herbaceous vegetation (‘grey dunes’)
Decalcified fixed dunes with Empetrum nigrum
Atlantic decalcified fixed dunes (Calluno-Ulicetea)
Dunes with Hippophae rhamnoides
Dunes with Salix repens ssp. argentea (Salicion arenariae)
Humid dune slacks
Machairs
Coastal dunes with Juniperus spp.
Priority habitat
UK special responsibility
No
No
Yes
No
No
No
No
No
No
No
No
No
No
Yes
Yes
Yes
No
No
No
No
Yes
Yes
No
Yes
Yes
Yes
No
Yes
Yes
No
No
No
No
No
Yes
No
No
No
No
Yes
Yes
No
identify substantial areas of significant habitats. The scale of change envisaged within the CHAMPS programme has
been both conservative in perspective and conditioned by a political requirement to provide firm quantitative assessments of change rather than more realistic prediction of uncertainties. This paper reconsiders this apparent ‘certainty’
of coastal habitat planning for the 21st century and develops a debate that identifies a future ‘uncertainty’ of coastal
habitat planning. The analysis is concerned with the reality of the future physical coastal environment, and the way in
which functioning habitats of value are likely to develop in a sustainable manner.
Coastal habitats of strategic importance
Central to the debate are those coastal habitats that are considered strategic for conservation in terms of both biodiversity
(Natura, 2000) and geological/geomorphological scientific value (identified in the UK through Sites of Special Scientific Interest [SSSI] designation). These two themes have become the central issues for conservation in the UK, so that
what was an intra-national process has become an inter-national process through European Union (EU) legislation and
international ex-EU agreements/treaties. The emphasis on sustaining habitats despite natural processes of change has
become more difficult given EU legislation emphasizing protection of scarce habitats (Natura, 2000). Coastal habitats
can be designated through a variety of instruments characterizing different elements of the biological and physical
environment that define habitats: SSSI, SPA, SAC and RAMSAR. Such designations often overlap, but inevitably
these characteristic dimensions do not always map synonymously. Table I identifies the range of significant coastal
habitats under EU designation, for which the UK has a special responsibility for protection as a critical or diminishing
element in the coastal zone (JNCC, 2004). It is clear that a number of these site types are under contemporary stress
(only 58 per cent of SSSIs in 2003 were in a ‘favourable’ condition with respect to the UK Government’s Public
Service Agreement requirement of 95 per cent ‘favourable’ status by 2010: English Nature, 2005), regardless of the
nature of future conditions. The problems posed by sustaining such habitats will undoubtedly conflict with legal
requirements and the reality of natural change.
Challenging Considerations and Assumptions in Future Coastal Habitat Planning
In what is likely to be a debatable list, we present below a number of generic considerations that we regard as being
central to contemporary practical approaches to the planning of future coastal habitats, particularly through shoreline
Copyright © 2006 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms 31, 1625–1642 (2006)
DOI: 10.1002/esp
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realignment (e.g. Leggett et al., 2004). They assume that the key future change for the UK coast is the persistence of
transgressive coastal systems. Although we could debate many aspects of future coastal change, there is general
agreement that the sense of change, in the UK at least, is one of future retreating shorelines. From that axiom, we can
deduce six ‘considerations’ or underlying themes concerning development of future sustainable coastal habitats, which
are usually implicit in contemporary coastal development plans (e.g. first generation of UK Shoreline Management
Plans developed under a central UK government agency – MAFF).
1. Natural habitats can maintain themselves, or evolve in a recognizable sequence as coastal forcing changes.
2. Natural environments will change spatially in an ordered sequence, i.e. what is there now will move onshore in
time, given a continuation of transgressive conditions and given continuity of accommodation space.
3. Following on from 2, it is only the vagaries of human decision taking that are a potential obstacle to the orderly
spatial evolution of natural habitats (e.g. coastal squeeze and inter-habitat rivalry of non-government organizations)
rather than physical conditions per se.
4. There are specific habitats that are valued for biodiversity (Natura, 2000), which are ranked for development
protection and preference.
5. There is an implied recognition of a difference between natural and anthropogenic coastal activities that can cause
habitat changes, with the latter often being regarded as unacceptable.
6. Where habitats cannot be maintained in situ, there is an expectation that they will be recreated elsewhere: the ‘no
net loss’ policy.
We may expect some debate in all of these considerations and do not necessarily believe that they are universal and
coexist at all times. There may even be others, but these have, through our working experience, been the major
considerations of future coastal habitat context, and as such, are rarely challenged (though point 6 is often cited; e.g.
Huggett, 1996). It is not our intention to challenge these points explicitly, but rather to examine critically the assumptions concerning the physical components on which they are based. These underlying assumptions concerning coastal
forcing and coastal responses, include:
1. that there is a sufficient understanding of the range of coastal forcing changes likely in the 21st century;
2. that the magnitude of future coastal change can be spatially accommodated within the present peri-marine limits of
the coastal zone;
3. that coastal sediment is available for future morpho-sedimentary deposition to sustain desirable habitat requirements and provide protective coastal morphologies for low-energy coastal habitats.
The central purpose of this paper is to establish whether these three assumptions are valid and, if not, how a more
appropriate specification might affect our prediction of future habitat development. FutureCoast (Burgess et al., 2003)
identified the real lack of meso-scaled spatial and temporal information on the formation and state of the English and
Welsh coastlines. In this absence of substantive data covering regional assessments of meso-scale shoreline status, we
have been forced to undertake assessment of assumptions based on discussion of key examples: some evaluative
analysis of limited meso-data for eastern England; application of some conceptual models of generic shoreline development to the UK coastline with respect to sediment supply; and an informed perspective based on six decades
(between us) of working on these coastlines.
Range of Future Coastal Forcing
Relative sea-level rise rates
There is a tendency to concentrate on absolute scale of sea-level change (e.g. English Nature, 2004), rather than on
the relative annual sea-level rise rate. The concept of ‘how much sea-level rise?’ has been prominent since the earliest
US Environmental Protection Agency and initial Intergovernmental Panel on Climate Change (IPCC) estimates of
climate change and its consequences (cf. Houghton et al., 1996; IPCC, 2001). As modelling scenarios have become
more precise, but not necessarily more accurate, the future centennial increase has generally decreased to less than
1 m, with the latest (IPCC, 2001) identifying global eustatic rise of c. 0·8 m for a business-as-usual scenario. This
ignores the mega-increases that the West Antarctic ice sheet or Greenland ice sheet might deliver after AD 2100
(Nichols and Lowe, 2004), i.e. an order of magnitude greater than current IPCC estimates. Although this increase
appears to be dramatic and clearly has major implications for flooding of low-lying built infrastructure, hence the
Copyright © 2006 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms 31, 1625–1642 (2006)
DOI: 10.1002/esp
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J. D. Orford and J. Pethick
drive for mitigation and adaptation, there is little overt concern over the annual rate at which this sea-level rise will be
delivered. Current rates of mean sea-level rise (MSLR) around southern and eastern UK are averaging <2 mm a−1 (this
is before the relative sea-level rise (RSLR) rate change due to crustal movement has been added; Hulme et al., 2002).
However, to achieve the predicted RSLR by the end of the 21st century, annual RSLR rates will have to increase to
between two and four times, assuming only a linear eustatic rise. Given a likelihood of non-linear centennial change,
then prediction indicates that RSLR rates are likely to be at four to six times the present rate towards the end of the
century, under a ‘business as usual’ scenario. These figures assume a mean rate of change that does not reflect an
annual variance term, which at the present time can show an exceedence rate of two to three times the long-term
annual rate, nor does it reflect the scales of high water increase (centimetres rather than millimetres) imposed by the
18·6-year nodal tidal disturbances (Jeuken et al., 2003).
It appears, therefore, that the emerging problem lies with the coastal response to high rates in RSLR (>4 mm a−1).
We recognize that the actual inundation of RSLR is thought to cause only a small proportion of actual shoreline
movement: for example Galvin (1983) provided an early estimate (20 per cent) of eastern USA barrier island shoreline
change due to inundation alone and that was assuming a RSLR rate of c. <2 mm a−1. This type of low regional
proportion is now thought to be problematic (G. Stone personal communication, 2005), but its scale underlies the
dominance of other sources of change to shoreline position due to the shifting nature of shoreline morphology through
re-energized and hence remobilized sediment pathways and temporary sinks as RSL rises. The real problem is
ascertaining how this remobilization of existing sediment stores will respond to future variable RSLR rate changes.
One assumption, that will probably be proved wrong, is that morpho-sedimentary deposits will respond in the same
way, even at increased tempos with higher RSLR rates. Jennings et al. (1998) indicated how a gravel barrier system
(Porlock, western England) showed ‘domains’ of barrier behaviour through the last 8 ka, which had radical implications for back-barrier environments, where the coherence and continuity of the barrier provided physical protection to
cross-barrier salinity incursions and sediment exchange. These barrier domains related to variations in RSLR between
a mid-Holocene rate of 8 mm a−1 to a present-day rate of 2 mm a−1. These rates are only resolvable over centuries and
annual rates may well have been up to twice the long-term rates. The palaeo-back-barrier environments showed a
radical shift between freshwater (closed barriers and longshore continuity) and saltwater domination (tidal breaches)
as a function of the rate of RSLR that controlled the speed of barrier migration and the maintenance of longshore
sediment supply. It appeared that, once RSLR approached 8 mm a−1, the spatial coherency of the retreating barrier
could not be maintained regardless of longshore supply. As RSLR dropped to between 8 and 4 mm a−1 then maintenance of spatial form was more evident, with any barrier breaches sealed by a maintained longshore supply, thus
allowing back-barrier freshwater developments due to impede drainage. Only as the RSLR dropped to less than
3 mm a−1 did the reduction in sediment supply initiate cannibalization phases of the barrier that led to barrier segmentation and tidal breaching. The lack of adequate sediment supply allowed breaches to be maintained, thus reducing
back-barrier freshwater habitats. The essential concept witnessed here is that changing evolution of barrier and backbarrier function is dictated primarily by sediment supply, which in turn is probably controlled by longshore supply as
a function of RSLR change. This is, however, predicated on a back-barrier accommodation space that allows barrier
migration.
Admittedly the future will see a rising acceleration curve, rather than the mid- and late-Holocene decelerating curve, and there is a potential for hysteresis (i.e. difference of barrier response on a rising RSL compared to a
falling RSL, as in the late Holocene) to alter the barrier reaction, but the critical warning is that with high RSLR
(>8 mm a−1) the reaction times of some coastal morphologies might well be too slow to maintain coherent barrier
functionality in the face of spatial shifts in shoreline position. It is not a sufficient assumption that protecting coastal
morphology, in particular barrier beaches (required for low-energy back-barrier habitats) will operate in the same way
when RSLR rates alter. Clearly the retreat rate of barriers rises as the rate of RSL rises (Orford et al., 1995a), but not
only does any linear response of barrier retreat to RSLR rates of 2 to 8 mm a−1 have to be questioned, but also the
organizational ability or resilience of the barrier, to respond consistently to changing conditions, is called into question. It is under these changes that some protected key habitats (Table I) could be prone to change, as salinity, for
example, would alter. Such barrier resilience is clearly a function of sediment supply, another assumption to be
considered below.
Storminess changes
There is perhaps a clearer indication of what may occur with regard to claims of changing storminess in association
with accelerating climate change, though whether there is an appreciation of what such changes might generate in the
way of coastal habitat change is a different matter. Sea-level change is the tempo controller of coastal change, while
storminess is the main agent of such change. Again there is a sense that what is currently happening with respect to
Copyright © 2006 John Wiley & Sons, Ltd.
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storminess will be no different in the future, with beach systems able to respond proportionally to increases in energy.
However, future storminess may lead to both magnitude and frequency changes in energy applied to coastal systems.
Lozano et al. (2004), as an example of the modelling of storminess changes, have identified a scenario of change in
Atlantic storms under a doubling of CO2, when considering a north–south gradient along Western Europe. They identify
that for the area directly west of the British Isles, there is likely to be no greater appreciable number of storms, but that
some storms will be more intense, such that the return period of storms associated with extreme water elevations will
reduce. The sequencing of extreme storms has an impact on the survival of elevated shoreline morphology (Lee et al.,
1998), in that any reduction in inter-storm period will impinge upon the ability of upper beach morphology to resist
overwashing by rebuilding (overtopping versus overwashing; e.g. Orford et al., 1995b). In this context consider lowenergy back-barrier habitats that are dependent on barrier maintenance for their survival. Under extreme storms that
overwash a barrier, the barrier itself will reorganize to a lower and wider structure assuming no major loss of sediment
on the coastal side (Orford et al., unpublished). Inter-storm periods are the times for upper-beach rebuilding by fairweather conditions (Komar, 1998), so any reduction in this rebuilding periodicity could threaten the upper barrier
stability. At the present time, there is a pragmatic coastal engineering principle to use natural barriers as a sea-flood
control measure, by reprofiling to prevent storm-generated swash exceeding barrier elevation. However, controlling
elevation without regard to barrier width (at some strategic level, e.g. High Water Springs (HWS): Orford et al., in
press) will not prevent barrier overwash and barrier retreat. Increased storminess under current management practices
will mobilize barriers and destabilize spatial boundaries of key habitats at a rate greater than simple inundation.
Increasing storminess, in tandem with RSLR, will force reductions in extreme water-level (EWL) return periods.
Although the radical reductions that Barkham et al. (1992) presented are probably overestimates of forced return
period reductions in extreme coastal water levels, even assuming only a 50 per cent achievement of their forecasts,
there would still be indications that all areas of the UK would expect to see to a return period reduction from a 1-in100-year event down to 1-in-less-than-30-year event for the same tidal extreme. Although Hulme et al. (2002) have
stressed the uncertainty of these types of projections, recent modelling of combined relative sea-level change (RSLC)
and surge generation indicates substantial reductions in return occurrence periodicities for extreme tidal levels, such
that Immingham’s current 1-in-50-year EWL is likely to be 1 in 3 years by 2050 (Hulme et al., 2002, p. 76). Thus,
given the importance of coastal habitats in the UK, the pressure to maintain coastal barriers at a time when they are
less likely to maintain current elevations, will become a major strategic issue in coastal planning. This barrier maintenance issue is not currently widely recognized as an element of habitat protection (see below).
Littoral Constraints and Accommodation Space
The emphasis on vertical scale changes with RSLR is clearly a front-line challenge but consideration of the horizontal
scale of change and the realignment response to it, though integrated in this challenge, have not yet addressed the
issue of the accommodation space needed to absorb future RSLC (e.g. Lonsdale et al., in press).
There has been considerable effort expended, through integrated management, to realize shoreline realignment in
the UK for both sea-defence and habitat purposes (Leggett et al., 2004). This process has been dominant, for reasons
of cost and appreciation of the reality of the situation, in the area of outer estuaries and agricultural reclaimed marshes
in eastern England. In the last decade several prime examples of realignment have been widely advertised, but they
are rarely seen as response exemplars to an ongoing process that requires rolling realignments to meet the retreat
demands of the 21st century. As such, realignment is generically no more than coastal set-back and most coastal
managers are working under the view that the future shift in shoreline will be within the perceived magnitude of the
shoreline and related areas, within the coastal zone as it currently exists. There should be concern as to the apparent
‘permanency’ of new habitats created by current shoreline realignment, as there is little explicit identification as to
the scale of future change likely to impact through the peri-coastal zone of today. Contemporary schemes for shoreline realignment are fine examples of retreat in lowlands and estuaries, but in themselves these examples are trivial
in area, relative to what might be required to satisfy future RSLR. Thus Lee (2001b) reported that 12 500 ha of intertidal managed realignment will be needed over the next 50 years in order to compensate for predicted inter-tidal losses
in England and Wales while, in sharp contrast, over the last decade managed realignment schemes have totalled less
than 500 ha. Likewise the complex policy by which the combined funding agencies (Defra, Environment Agency,
English Nature and NGOs) work towards identifying areas for realignment has concentrated on estuaries and ends up
with piecemeal out-takes in complex and highly integrated estuary systems (i.e. the Crouch and Roach in Essex,
eastern England: Leggett et al., 2004). These schemes offer good practice and suggest absorption of future RSLR
specifically for flood protection and biodiversity, but are too small and too few to offer long-term solutions to the
wider area.
Copyright © 2006 John Wiley & Sons, Ltd.
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Such exemplars of realignment – and exemplars are all they can be by virtue of the limited areas involved – are
facing diminished sediment supply (see next section), as well as adjusting to changes in rates of RSLR, problems
exacerbated by their disequilibrium due to past holding-the-line policies. Thus, Pethick (in Posford Haskoning, 2002a)
reported that erosion of the outer Dengie marshes in Essex was paralleled by increased accretion rates on landward
margins as the marsh area available for deposition decreased due to coastal squeeze against the flood embankment,
creating increased surface slopes and further accelerating outer marsh erosion. Such feedback mechanisms mean that,
at best, much of the realignment is only scaled to estimates of the needs for the past century’s equilibrium salt marsh
requirements to be re-established along eastern England estuaries. It is probable that future increases in coastal forcing
will require multiples of these realignments, if not continuous rolling retreat in order to absorb the changes. This scale
will be extensive in the estuaries of lowland Britain: potentially hundreds of metres, not just metres of retreat should
be expected. This scale is likely to be substantially less where such realignment is adjusted against rising ground, so
that the form of the underlying terrestrial platform is central to this issue, but this will be of little effect in most of the
low-lying estuaries of eastern England. The belief that future sustainable development of habitats can occur under
these new conditions must be resisted, as associated contemporary developments need to be viewed as temporary, i.e.
decades at most, such that specific habitat development policy of recent years as a main criterion for realignment
would need to be viewed as a rolling programme of change through the next century, rather than a one-off as identified
under current programme specification. The point is that the coast will continue to move back and associated habitats
will change, and we need to envisage this as a continuing process.
Sufficient Coastal Sediment
The problem
Perhaps the most serious, and yet largely unrecognized, issue facing coastal conservation and management over the
next century may be the reduction in sediment available to coastal landforms. The implications of such a reduction are potentially more serious than the change in coastal energy resulting from changes in sea level or storm
frequencies, since the natural morphological recovery from these energy changes will be impeded by a decrease in
sediment availability. If sediment inputs to the coast decrease, coastal landforms will fragment and reduce in surface area, while low-energy environments will be diminished as protective barriers breach. The resultant changes
in habitat will have little regard for designated priorities. Instead the diversity of the overall coastal mosaic, as well
as surface areas of specific habitats, will be challenged. Fragmentation and isolation of coastal landforms will be
accompanied by modification of coastal plan-form as swash-aligned shores begin to predominate. Onshore transgression of estuarine landforms and associated habitats in response to sea-level rise, without additional sediment
imports, could result in lower inter-tidal surfaces, increased tidal prisms, and development of a positive feedback as
channels widen even further in response, in many cases leading to accelerated loss of salt marsh and upper inter-tidal
habitat.
The critical issues here are to determine, first, whether a sediment deficit is indeed facing coastal habitats and, if so,
what the magnitude of the deficit might be, both now and in the medium-term future; and, second, whether this lack of
sediment will be exacerbated by inadequate accommodation space available for horizontal adjustments of inter-tidal
habitat. If answers to these questions are forthcoming then, even if they were to confirm the concerns listed above,
careful coastal management may limit the loss or, at the very least, allow our approach to coastal conservation to come
to terms with the imposed changes.
Sediment supply
Accurate measurement of sediment inputs to coastal landforms has been, and remains, almost impossible. Sources are
so diverse, including seabed erosion as well as the more obvious cliff erosion sites, that the best that can be achieved
is a rough estimate (Table II). The recent Southern North Sea Sediment Study (SNSSS; HR Wallingford, 2002) for
example, reviewed an extensive literature on sediment sources in that area and found estimates varying by 300 per
cent, even for the more accessible sites such as the Holderness cliffs, while estimates of fine sediment inputs to the
North Sea via Dover Straits were assigned a range of an order of magnitude in one study (Velegrakis et al., 1997).
Taking the study area as a whole (Flamborough Head to North Foreland), analysis of the SNSSS database indicates a
mean estimate of 1·6 Mm3 a−1 of medium sediment (sand) inputs mainly from cliff erosion, and 12 Mm3 a−1 of fine
sediment inputs from seabed and cliff sources but, as pointed out above, these average figures may be associated with
a range of at least an order of magnitude (Table II).
Copyright © 2006 John Wiley & Sons, Ltd.
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Table II. Estimated annual sediment availability between Flamborough Head and North Foreland (eastern England) and budget
requirement for varying rates of sea-level rise rates. Data based on SNSSS (HR Wallingford, 2002)
Sediment availability (Mm3 a−1)
Sediment demand (Mm3 a−1)
Sea-bed requirement (Mm3 a−1)
RSLR
(mm a−1)
Cohesive
sediment
Surplus/deficit
demand (%)
2
6
8
2
6
12
3·3
10·0
13·2
60·0
180
+72·5
+16·6
−13·0
400
−1400
Non-cohesive
sediment
Surplus/deficit
demand (%)
1·6
1·2
3·6
4·8
+75
−125
−200
Sediment demand
The difficulty of assessing sediment balances using such a wide range of estimates for supply is exacerbated by the
lack of any clear concept of a sediment demand, an issue that has received scant attention in the literature. Two
approaches may be proposed: (i) estimating potential sediment transport rates using wave and tidal data for specific
shores; and (ii) providing volumetric estimates of the sediment needed to maintain coastal landform elevations during
sea-level rise. The first of these approaches may be used to estimate demand for a short section of coast, but
integration over a larger area is not possible. Thus the net annual potential transport rate along the open coasts of East
Anglia is in the region of 150 000 m3 to 250 000 m3 (e.g. Thomalla et al., 2001). If this was assumed to represent a
system throughput for the entire SNSSS area, then the gross input of 1·6 Mm3 more than satisfies the potential
demand, yet such an approach ignores internal sinks completely. In contrast, if the entire coastal zone is regarded as a
potential sediment sink in order to keep pace with sea-level rise, then a rough calculation for sand-sized sediment
based on a total open coast area of 600 km × 1 km and a long-term rate of sea-level rise of 2 mm a−1, gives a potential
sand demand of 1·2 Mm3 a−1, not radically different from the gross imports of 1·6 Mm3 a−1 calculated above (given the
associated uncertainty of this estimate) and suggesting that no sediment shortage is being experienced at the present
time, albeit conditions may be approaching a critical value and may exceed this limit within specific locations.
If the fine sediment fraction is considered, then an even more optimistic picture emerges. The total surface area of
the estuaries between Humber and Swale is 164 000 ha (Davidson et al., 1991), giving a gross sediment demand,
assuming sea-level rise of 2 mm a−1, of 3·3 Mm3 a−1. Total fine sediment imports into the sea area, including that from
seabed erosion, cliff erosion and imports across the Dover Straits, amounts to 12 Mm3 a−1 (HR Wallingford, 2002).
Although these figures ignore losses across the eastern boundary of the sea area, the initial conclusion must be that
fine sediment is, at present, potentially in abundant supply to meet the imposed demand.
Despite these figures showing a positive sediment balance in the southern North Sea, there are three reasons for
possible future concern:
•
•
•
increases in the rate of sea-level rise over the next 50 years will substantially alter the sediment demand;
morphological evidence already indicates a sediment deficit (Burgess et al., 2003), particularly where past driftaligned fringing North Sea coastal morphology has reorganized into swash-aligned, indicating reducing coastal
supply (cf. Orford et al., 2001);
evidence from the southern North Sea cannot be used to infer positive sediment balances elsewhere.
Relative sea-level rise
Given the predicted increase in the rate of RSLR over the next 50 years, sediment demand is likely to increase but
sediment supply may show an overall decrease. Assuming sea-level rise increases to a rate of 6 mm a−1, this
means that the linear demand for sand-sized sediment will increase to 3·6 Mm3 a−1 compared to present inputs of
1·6 Mm3 a−1. Moreover, the inputs may themselves fall over the next 50 years if our present policy of coastal defence
provision continues to lock up an increasing length of eroding cliff sediment. The demand for fine sediment will
increase as the rate of sea-level rise increases, to 10 Mm3 a−1 compared to the estimate of 12 Mm3 a−1 for inputs. While
this appears to leave a slight positive margin, it ignores the decreasing inputs from seabed erosion, presently put at
3·75 Mm3 a−1 (Dyer and Moffat, 1998). If the southern North Sea bed were to accrete at the same rate as sea-level rise,
then the demand for sediment would far outstrip any estimates of gross imports. The total sea area for the SNSSS
study was 30 000 km2 so that, to keep pace with present-day rates of sea-level rise at 2 mm a−1, the demand would be
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3
−1
3
−1
for 60 Mm a . This would increase to 180 Mm a over the next 50 years, far outstripping supply. The conclusion
must be that the seabed is not keeping pace with sea-level rise and water depths will increase steadily over the next
50 years, leading to reduction in seabed erosion by wave action and to a decrease in fine sediment inputs that will
result in a negative balance on the coastal fringes of this region.
Even more serious might be the outcome of an increase in the rate of sea-level rise to more than 6 mm a−1 if relative
rather than eustatic processes are considered, as explored earlier in this paper. Rates of sea-level rise of >8 mm a−1
would, in the North Sea estuaries at least, result in sediment demand outstripping sediment supply (13·2 Mm3 demand
and 12 Mm3 supply), even assuming existing sources continue to supply sediment unabated. The result of such an
imbalance would rapidly be reflected in estuarine morphology and it is interesting to note the parallels with similar
impacts of a >8 mm a−1 rise in RSLR on non-cohesive coastal morphology (Jennings et al., 1998), as discussed above.
Evidence to demonstrate whether estuaries can keep up with such rapid rates of RSLR is not available since most
detailed studies of Holocene estuarine development from England show maximum RSLR rates of between 5 and
6 mm a−1, although Metcalfe et al. (2001) do show that mid-Holocene deposition in the Humber estuary was able to
keep pace with a 5 mm a−1 rise.
Morphologic response
In the face of the pessimistic predictions for coastal habitat reached above, it is easy to turn to the margins of error in
all of the estimates. Since the specific estimates referred to in the above discussion may in fact represent a data range
of an order of magnitude, it is possible, perhaps necessary, to dismiss the results as meaningless. With such a range in
estimates, a comparison between sediment supply of 1·6 Mm3 a−1 and sediment demand for 1·2 Mm3 a−1 cannot yield
any firm conclusion. But the lack of certainty in the measurements may, of course, be interpreted in two ways: either
there is an abundant sediment supply and the possibility of a sediment deficit can be dismissed; or alternatively, the
sediment deficit is even greater than suggested by the data.
Attempting to distinguish between these alternative interpretations requires an alternative source of evidence, and
this may be gained from the geomorphological behaviour of the coast. Geomorphological indications of sediment
reduction can be recognized in coastal landform development over the past 100 years or more, as shorelines appear to
have adjusted from drift to swash alignments as longshore sediment volumes have reduced (Orford et al., 2001). The
increasing difficulties of maintaining barrier beaches with and without artificial down-drift sediment transfers (Porlock,
Somerset; Cley, Norfolk; Cuckmere, Sussex; Rye, Kent) are the most obvious symptom of this shoreline reorientation
process. Subtler are the long-term changes in coastal landform location and orientation, the symptoms of which have
often been identified merely as isolated examples of erosion without examination of the wider implications (Burgess
et al., 2003). On the open coast, the evidence for reduction in sediment inputs involves a change from drift- to swashalignment that includes, for example, reorientation via the redistribution of sediment, coastal segmentation by emergent headlands, and embayment formation leading to loss of existing resources through flooding and erosion (see
below when considering Aberystwyth beaches; cf. Orford et al., 1996, 2001). In estuaries, a reduction in fine sediment
imports can lead to an overall lowering of inter-tidal surfaces, progressive erosion of outer estuary salt marshes, and a
failure to keep pace with the stratigraphic roll-over process as sea-level rises (Townend and Pethick, 2003).
Estuarine systems
The maintenance of inter-tidal surface elevations (both (un)vegetated surfaces) in estuaries is a dynamic process
involving periodic erosion by storm waves and subsequent depositional recovery before the next erosion event occurs.
If storm frequency remains constant, the periodicity of this process will be governed by the rate of recovery of the
depositional surface; if this rate is retarded, for example by a fall in the suspended sediment concentration, then the
surface elevation fails to recover between erosion events and the mean surface level falls (Pethick, 1996). In most
estuaries in England and Wales, outer estuary inter-tidal mudflats are eroding vertically, leading to salt marsh edge
recession, although the same salt marshes are accreting vertically (Pethick, 1991; Posford Haskoning, 2002a). Although
this process can be said to be a result of sea-level rise leading to an increase in wave energy within the estuary, it is
difficult to see why, after a steady rate of sea-level rise in most estuaries for the past 2000 years (Shennan and Horton,
2002), there should be such change in the morphological response over the past 50 years, since there is, as yet, no
evidence to suggest that rates of sea-level rise have increased over the past few decades. Although changes in
vegetation, notably Spartina cover, may account for these observed changes, an alternative explanation may be that
suspended-sediment concentrations, whether due to natural or artificial (e.g. dredging) causes, have fallen, leading to
a retardation of the recovery process outlined above. There is, however, no direct evidence for such a fall in
suspended-sediment concentration; indeed, given the natural temporal and spatial variability in suspended-sediment
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concentration, detecting a long-term trend would require a substantial database. Thus, on the basis of circumstantial
morphological evidence alone it is not possible to draw any firm conclusions as to the possible reduction in cohesive
sediment availability at present.
Open-coast systems
Morphological evidence for reduction in non-cohesive sediments is more substantial on the open coast, where largescale adjustment from drift- to swash-alignments can be identified. Potential demand for sediment is dependent on
shoreline orientation to wave approach angle. If this demand is not met then erosion of the existing sediment resource
occurs and the shoreline orientation changes, reducing the angle between wave and shore and leading to a reduction or
even elimination of net longshore sediment transport. Redistribution of sediment within a coastal system is rarely
accomplished without significant losses offshore so that, although some accretion may occur, the net balance for the
system is a negative one. Gravel-based coastal systems offer the clearest example of morphological change associated
with sediment reduction. For example, research for the Dungeness Coastal Habitat Management Plan (Posford Haskoning,
2002b) showed that the massive reduction in sediment supply to the Dungeness shingle system over the past 200 years
(from c. 150 km3 a−1 in c. AD 1800 to <5 km3 a−1 in AD 2000), due to both the intercepting Rother training wall and a
radically reducing Little Ice Age injection of coastal sediment, has resulted in recession of the western end of the
southern Dungeness shore, as the shoreline reorientates to a swash alignment. Although much of the gravel is redeposited
along the eastern Dungeness shore between the Ness and Littlestone, a significant proportion appears to be moved
offshore in the process of rounding the Ness (Posford Haskoning, 2002b). The resultant habitat changes involve loss
of perennial shingle vegetation along the south shore and gain of annual vegetation of strandline along the east shore,
but with an overall loss in the designated habitat area (Table I, Code 1220).
Periodic headland emergence and collapse has characterized many shores over the Holocene (e.g. Dorset, Isle of
Wight; Lee, 2001b) but long-term headland emergence and resultant coastal segmentation may replace this periodic
process as a result of sediment reduction. The beaches fronting Aberystwyth (Figure 1A), west Wales (Pethick et al.,
2003), formerly received sediment inputs via a sediment pathway along the barrier beach at Tan-y-blwch, and connected to a source area of periglacial deposits draped across interglacial cliffs to the south (Figure 1B). The periglacial
drape has been virtually eliminated in the source area, with the underlying rock exhumed in the current active wave
zone. This major reduction in sediment input from these cliffs and nearshore sources has resulted in a reorientation of
the Tan-y-blwch barrier to a deepening swash alignment (Figure 1C), resulting in cessation of sediment inputs to the
Aberystwyth frontage, necessitating both artificial nourishment and defences (Figure 1B). The increasing segmentation of this coast, with the development of emergent headlands such as that at Altt Wen south of Tan-y-blwch, appears
to be due to a reduction in periglacial source material, both on the seabed and on the cliffs themselves, that can be
mobilized by the contemporary conditions. What sediment is available in the nearshore is bypassing these Aberystwyth embayments and being lost to the beach face to judge by the depleted state of the beaches. The weakening state
of Tan-y-blwch barrier, which is undergoing both vertical rotation of the beach face (i.e. steepening of the foreshore)
and movement of the profile onshore (Figure 1D), offers the scenario of future barrier breakdown and emergent saline
back-barrier zone, unless new longshore sources are brought into future elevated swash zones by RSLR. This is an
example of what we refer to as increasing segmentation of the coastal zone, rather than the increasing integration of
the coastal zone that is being expect for the 21st century (as exemplified by EU demands for Integrated Coastal Zone
Management (ICZM) support).
In several cases, the precedents of the adjustment from drift- to swash-alignment are exhibited by morphological
changes on the nearshore seabed but these are, as yet, either obscured or damped down by shore defences of various
kinds. Analysis, for this paper, of changes in Suffolk nearshore topography, using Environment Agency data sets over
the last two decades (Environment Agency, 2005), show a regular spatial sequence of seabed erosion and deposition
(Figure 2: elevation change over 15 years) that is not yet represented in the upper shore morphology. If these changes
are eventually translated into upper shoreline changes, this sequence would indicate that an anticlockwise rotation
towards the northeast wave direction will occur en echelon, and appears to be a typical outcome of a swashrealignment process with sediment redistributed from the north of each ‘bay’ towards the south. This process would
result in a series of process-headlands separating each bay, which will effectively segment this previously continuous
shoreline.
At Winterton, on the east Norfolk coast (Figure 3), studies have suggested that without massive and continued
intervention, sediment input depletion will result in breaching of the dunes and potential saline flooding of large areas
of lowland fringing the protected Norfolk Broads (Martham Broad; Posford Haskoning, 2003). The Winterton–Horsey
dunes form a barrier across what was a former tidal inlet; this barrier ridge initially followed a convex plan form
suggesting that longshore sediment transport was increasing towards the south due to inputs from the nearshore. Over
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Figure 1. (A) Location of Aberystwyth, west Wales. (B) Segmented beach units at Aberystwyth. (C) Profile positions on Tan-yblwch swash-aligned gravel-based barrier. (D) Rate of migration of Tan-y-blwch profiles; note deepening of swash-alignment
between P4 and P8 due to failure of longshore supply. Data from Pethick et al. (2003). Photos in (B) and (C) are courtesy of
Ceridigion County Council.
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Figure 2. Longshore structuring of nearshore bathymetry between Lowestoft and Aldebrugh, East Anglia, based on Environment
Agency bathymetric surveys (1985–2000). Location of longshore section shown in Figure 3.
the past 150 years, however, map evidence shows that the coastline here has become increasingly straight (Figure 3),
indicating a reduction in these sediment inputs and a progression towards an eventual concave, swash-aligned coast.
This would take the form of an asymmetric bay between the headlands formed by Happisburgh and Winterton, with its
bay head several hundred metres inland of the existing shore and involving erosion of the area designated under the
Habitats Regulations as a Special Protection Area, as well as the flooding of some 8000 ha of lowland Norfolk,
although such flooding may result in the development of inter-tidal habitat.
Some of these examples of coastal behaviour appear to indicate that morphological change has been brought about
by a reduction in sediment availability rather than sea-level rise, increased storminess or anthropogenic interference,
though the latter set of processes will also accelerate this tendency. It is not, however, a ubiquitous phenomenon.
Non-cohesive sediment is, for example, in plentiful supply in Morecambe Bay, the Fylde coast and Liverpool Bay
(e.g. Van der Wal et al., 2002), despite the apparent impoverishment immediately north in Cumbria. In contrast,
cohesive sediment has been in short supply throughout the Holocene in the Atlantic coast estuaries such as the Fal
(Stapleton and Pethick, 1996), and is responsible for their lack of depositional infill, while the evidence for reduction
of sediment imports into east coast estuaries is equivocal. The conclusion must be that there is sufficient evidence to
suggest that we are probably past the point of major of change. After 6000 years of coastal adjustment to a variable
rate of sea-level rise, with abundant sediment supply to most of the English and Welsh shorelines, we are faced by a
probable increase in the former and a decrease in the latter, with consequent major morphological adjustment. Quite
apart from the increase in hazard to coastal infrastructures, such adjustments are likely to have a major impact on
coastal habitats and their management.
Integrative protective coastal morphologies
Key coastal habitats for both flora and fauna, in particular for initial fish nurseries, and migrant and indigenous bird
feeding grounds, are freshwater/brackish lagoons, low-energy wetlands, salt marshes, and intertidal flats. Most of
these types of habitats are maintained only by the protection afforded by barriers and spits. There is a concern
expressed in the Future Coast project (Burgess et al., 2003) that such barriers and spits are managed as a visible
isolated element of an otherwise integrated coastal system, mainly because such features tend to be found at the
longshore administrative boundaries of local government or even at sediment cell-breaks defining Shoreline Management Plans. The connections between integrative coastal systems, especially between estuaries, often cross-cut administrative boundaries and thus habitat management has difficulty in covering the constituent morphological elements
that physically protect coastal habitats, e.g. barriers defending mudflats and sandflats, Spartina swards, and coastal
lagoons. This presents a problem for existing coastal habitats, as designations need to be rewritten now to encompass
the lack of earlier understanding as to how systems operate in key habitats form. This problem is compounded when
future forcing-changes will drive changes in barrier/spit systems that are not sustainable for habitats without major
changes in sediment supply.
Westward Ho! pebble barrier in north Devon (May, 2003) exemplifies the nature of this problematic unit (Figure 4).
The present pebble barrier acts as a major wave barrier to the southern side of the Taw–Torridge estuary. The barrier
has a proximal end in dunes (Northam Burrows) that are offset from matching dunes of Braunton Burrows on the
north side of the estuary. The distal end of Westward Ho! barrier is spatially controlled by the remnant ebb-tide delta
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Figure 3. Rotation of Winterton shoreline, based on Ordnance Survey and Environment Agency surveys since 1837, showing the
retreating beachface between Winterton and Happisburgh. Inset shows location of Figures 2 and 3.
associated with the Taw–Torridge estuary mouth. To the rear of the pebble barrier there are remnant inter-tidal flats
with blown sand on relict marsh accretion, building the surface above contemporary mean sea level and allowing
deposition located in a protective wave-energy lee. This area (plus the barrier) is SSSI designated as a foreland nesslike structure, and physically offers the only protection to the southern side of the estuary to incident Atlantic swell
energy. There is a lack of any debate as to the origin of previous protecting barriers at this site, given that the current
pebble barrier appears to be the remnant of 16th or 17th century sediment pulses coming from open-coast cliff failures
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Figure 4. Westward Ho! pebble barrier as a protective low morphology, and its relationship to coastal geomorphological units
forming the Taw-Torridge estuary complex in west Devon, UK.
to the south of the estuary (Halcrow, 1980). These source areas are now spatially detached from the barrier’s proximal
connection, by a coastal offset exposed by the barrier rolling back into the estuary re-entrant (Figure 4). Barrier
rollover has occurred due to declining longshore sediment supply and barrier adjustment to sea-level rise (Orford
et al., 1995a; Keane, 1997). Currently there is no new gravel entering the barrier from an up-drift position, while there
is still longshore sediment drift (c. 5 km3 a−1) moving from off the barrier northwards into a sink flanking the open
estuary. This gravel sink operated as the source for late 20th century anthropogenic beach ridge renourishment to
maintain the barrier’s spatial position. It is estimated that 4 per cent of the barrier volume is depleted annually by
longshore drift. That loss rate, compounded by a likely increase in mean annual barrier retreat rate of 2 m a−1,
generated by a 5 mm a−1 increase in rate of RSLR (Orford et al., 1995a), means that the pebble barrier has a
conservative 30-year future if renourishment is not maintained. However, even if this nourishment scheme is continued, it is unlikely to maintain the barrier’s flood protection ability, given future RSLR demands for sediment to
maintain barrier elevation.
Any loss of the barrier would be more detrimental to the structure of the wider coastal system than a change in
extreme water-level return-period alone. Barriers are often controlled by hydraulic efficiency of confined estuaries
where barriers and spits are spatially self-regulated by presence of ebb-tide deltas and cross-sectional area of tidal
estuary entrance (Townend, 2005). Changes to RSL will force cross-section changes and alter potential for proximal
fixing of spit heads, but radically changing coastal protective morphologies due to sediment supply failures can
engender changes in the timing and discharge of tidal prisms if multiple tidal passes open as the barrier destabilizes
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and major restructuring of back-barrier environments occurs. The loss of sediment supply and the consequent coastal
segmentation will clearly be a major factor in any potential habitat restructuring. In this context, habitats need to be
seen as ephemeral consequences of degenerating protective coastal morphology.
Strategic Changes in Coastal Policy
Considerations validity
The issue of considerations validity is going to be hedged by the level of uncertainty currently associated with the
forcing changes envisaged as well as the spatial scale of responses. Sea-level change rates will be critical to future
predicted evolution of low-energy peri-marine habitats, and it is likely that the contemporary protection levels provided by many natural barriers will not be maintained in future circumstances. The long-term stability of fringing
coastal habitats is likely to reduce during the current century. The essential requirement is to develop an appreciation
of the scale of retreat that any sustainable setback policy will require, given the scale of likely changes. The whole
emphasis of sustainable habitats should be time-based rather than space-based. Thus future habitat development needs
to be viewed as cyclic and should be approached on an intra-decade base, rather than inter-decade as characteristic of
past and contemporary approaches to habitat creation.
Sediment husbandry
It is essential to recognize the role of sediment in conditioning some of the six initial considerations being challenged,
as it is sediment that provides the morphological ability to regulate the considerations (particularly points 1, 2 and 4).
The evidence for the imminent change in our coastal habitats is equivocal, but faced with such equivocation, prudent
coastal management should adopt the ‘precautionary principle’. Coastal conservation should work on the assumption
that the area of the coastal zone and its associated habitats are likely to decrease over the next 50 years, and attempt
to mitigate the impacts of this possible reduction. It is, of course, possible to conclude that such changes in the habitat
resource are not, in the words of the Habitats Directive, ‘deterioration or destruction’ (ECC, 1992, Article 4·4) since
the changes could be seen as part of ‘natural development’ (ECC, 1992, Article 9), but the argument for natural
change is often a difficult one to defend. Thus, we have systematically interfered with coastal sediment budgets over
the past 500 years by sequestering sediment, for example in ‘reclaiming’ sediment storage areas and separating them
from their sediment sources so that available sediment drifts offshore and is lost to the coast. We have reduced
sediment inputs by constructing coastal defences, dredged sediment from estuaries for navigational access, and removed further sediment resources to use as ‘aggregate’.
Future precautionary coastal habitat management should therefore attempt to ameliorate the impacts of future
sediment imbalances by redressing some of our past mistakes as well as initiating new measures. Such measures may
be termed ‘sediment husbandry’, and would attempt to initiate wise use of a dwindling resource.
A prime example of good sediment husbandry would be the provision of areas for sediment deposition along the
coast, capable of trapping whatever sediment is still available to us and retaining it for future habitat provision.
Managed realignment that opens up ancient salt marsh surfaces to fresh deposition would achieve such an end, but the
timetable for the process may be a short one. If managed realignment is postponed until increases in the rate of sealevel rise make it inevitable, then these new sediment sinks will be competing for a resource by then in short supply.
In 50 years time, a managed retreat that opens up 100 ha of Medieval reclaimed marsh on the UK east coast would
result in a total sediment demand of over 1 Mm3 at a probable rate of 10 000 m3 a−1 on a total resource estimated to be
in the region of 12 Mm3 a−1. This may be a small percentage of the annual supply, but if ten such managed realignment
sites were opened their combined demand would amount to 1 per cent of a resource already outstripped by the
demands of the existing coastal habitats. The result must be either that managed realignment sites in AD 2060 would
fail to accrete or, depending on location, would divert sediment from existing inter-tidal habitats that would then
deteriorate. Thus action is required immediately, while sediment supply is still in positive balance, so as to trap this
dwindling resource. Inner estuary reclaimed areas, in particular, should be the prime site of such managed realignment
in order to trap sediment already moved landward by rollover processes and incidentally thus reducing the problems
of increased sediment in navigation channels, marinas and freshwater outfalls.
The current emphasis on fine sediments for realignment should not dominate sediment perspectives. Sand dunes may
be regarded as the non-cohesive sediment analogue to salt marsh. Enlightened sediment husbandry would reconnect
these to their source areas, the inter-tidal beach, removing intervening defences and, more importantly, removing
obstacles to renewed deposition – the boardwalks, invasive and human-introduced sea-buckthorn and pinewoods that
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impede saltation onto the dunes. Similarly, gravel barrier beaches should be reconnected to their sources areas,
removing the updrift groynes that have diverted so much of this sediment resource into offshore sinks. These are
identified as being the type of action needed to move towards restoration of self-regulating coastal systems that can
support a maximum diversity of habitats.
Source areas themselves must be identified and, where necessary, remobilized. Cliff defences are an obvious
contender but more controversial would be removal of cliff vegetation cover, such as plantations of trees, to facilitate
slope failures.
The scale of the problem facing habitat management over the next century means, however, that we must extend
our range of management tools far beyond these conventional techniques. One of the most critical sediment sinks
along the coast, although largely ignored by coastal management, are tidal deltas (both flood and ebb). These trap
massive volumes of non-cohesive sediment and, in so doing, provide onshore shelter for cohesive sediment habitats.
Tidal deltas require tidal discharges from estuaries and here managed realignment may be used to increase estuarine
discharges; more controversial may be the reopening of former tidal channels that were ‘reclaimed’ or even the
provision of new channels, for example by allowing or even constructing breaches in barrier beaches. This has to be
done selectively, dependent on the potential ebb/flood asymmetry of such a breach, as deltas may well induce a local
demand for non-cohesive sediments and thereby potentially deplete beach volumes along adjacent open-coast systems.
To incur such losses can only be offset by sediment being directed onshore (flood) rather than offshore (ebb) delta
development.
Habitat considerations
If the three core assumptions described at the outset of this paper are not to be met under future change, how would
their more likely specification affect our prediction of future habitat development? This can be considered in the
context of the cited considerations.
Consideration 1 and 2: natural coastal habitats may be squeezed out by future forcing, such that a recognizable
evolution of peri-marine habitats and their spatial continuity (from facies models; Orford, 2005) may well be lost
under rapid transgressive conditions.
Consideration 3: natural physical process can lead to loss of specific habitats through natural squeeze as well as
anthropogenic intervention. A rapid transgression against steeply rising land, without adequate sediment to offset
shoreline retreat, may well squeeze back barrier habitats.
Consideration 4: the scale of future coastal changes may make a policy of ‘desirable’ habitats, defined by legislation, untenable, and ‘opportunistic’ and temporary habitats will have to be accepted as substitution policy. The tempo
of quickening change of physical environments will potentially reduce habitat existence scales to less than that of
human memory. Notions of ‘what should be’ based on ‘what has been’ will not be viable as a primary articulation of
habitat type.
Consideration 5: the distinction between natural and anthropogenic coastal changes around the UK has to be seen as
artificial. The scale of human adaptation/intervention in coastal sequences is such that there is little of the UK
depositional coast that can be considered as truly natural. In this context all future habitat emergence has to be treated
as a bonus, regardless of type. Trying to delay the onset of habitat change due to legislative requirements in the face
of future coastal change is likely to be non-sustainable and divert us from more rapid consideration of responding to
reality rather than what some sectors might wish the coastal zone to be.
Consideration 6: not all coastal habitats can be recreated easily in proportions approximating to their present
distribution and quantities, due to the effects of relief and distributions of settlements and economic interests. Creation
of inter-tidal habitats will inevitably destroy many freshwater habitats, creating a further requirement to recreate those
at locations away from the coast.
Conclusions
Many contemporary assumptions and considerations implicit in managing coastal habitats have been seen as untenable
in the context of 21st century coastal forcing change. As a consequence, the range of possible futures for coastal
habitats needs to be broadened to include a substantial reduction in certainty of habitat type and their longevity. There
is likely to be a major loss of low-energy environments and attempts to recreate coastal low-energy habitats is not
going to be sustainable, given the speed of future change and the disturbance to protecting morphology of existing
coastal habitats. In this context, any policy of ‘no net loss’ may be acceptable in terms of crude habitat area, but not
in terms of habitat type. Therefore, it may be better to recognize terrestrial habitat creation for the long term (century)
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while preparing for short-term (decade) presence, and then disappearance, of coastal habitats. The logic of EU
Directives to maintain or enhance these coastal environments in perpetuity is well-meaning, but not realistic given
likely forcing outcomes.
A reduction in sediment availability for coastal habitat maintenance is seen as one of the highest priorities for
coastal management over the next century. Sea-level rise, increased storminess and anthropogenic interference will be
secondary to the problems presented by diminishing sediment supply. The evidence examined here takes two forms:
first, quantitative estimates of supply and demand which yield equivocal conclusions for present-day supply but
suggest future negative balances may develop; second, geomorphological evidence that appears to show that sediment
reduction is already in progress, resulting in the erosion and realignment of much of existing coastal habitat.
It may be argued that there is already sufficient evidence to promote a precautionary approach to sediment management over the next century, an approach that should be dominated by a wise use of a dwindling resource that is
referred to as ‘sediment husbandry’. The basic principle behind sediment husbandry is a simple one: stop sediment
wastage by providing deliberate coastal sinks and reducing other losses of sediment output elsewhere. The habitats
that develop as a result must depend on the intricacies of coastal geomorphology and should not be predetermined
by management or legislative process. Many of the techniques involved will be controversial, not least to coastal
landowners and users, and management must consider ways of reducing this negative perception, perhaps by introducing such measures as financial compensation. Above all it is emphasized that measures must be introduced as a matter
of urgency, since the timetable for sediment reduction does not allow us the luxury of procrastination for the next
century.
Acknowledgments
Both authors recognize and acknowledge the opportunities presented by English Nature, the Environment Agency, and British
Energy Generation Ltd to consider some of the specific sites mentioned in this paper. The conclusions reached in the paper are those
of the authors alone, and are not to be construed as identifying the official view of any of these organizations. We are grateful for the
comments from two anonymous and perceptive reviewers. We acknowledge Maura Pringle (QUB) for the graphics used in this
paper.
References
Barkham JP, MacGuire FD, Jones SJ. 1992. Sea-level Rise and the UK. Report for Friends of the Earth: London.
Burgess K, Orford J, Dyer K, Townend I, Balson P. 2002. FutureCoast – the integration of knowledge to assess future coastal evolution at a
national scale. Proceedings, 28th International Conference on Coastal Engineering. World Scientific 3: 3221–3233.
Davidson NC, d’A Laffoley D, Doody JP, Way LS, Gordon J, Key R, Drake CM, Pienkowski MW, Mitchell R, Duff KL. 1991. Nature
Conservation and Estuaries in Great Britain. Nature Conservancy Council: Peterborough.
Defra. 2001. Shoreline Management Plans: A Guide for Coastal Defence Authorities. Report. UK Department of Environment, Food and
Rural Affairs: London. Available to download at http://www.defra.gov.uk/environ/fcd/policy/smp.htm
Dyer KR, Moffat TJ. 1998. Fluxes of suspended matter in the East Anglian plume, Southern North Sea. Continental Shelf Research 18:
1311–1331.
ECC. 1992. On the Conservation of Natural Habitats and of Wild Fauna and Flora. Council Directive 92/43/EEC of 21 May 1992.
European Communities Council. O.J., L 206, 22.7.1992, p. 7.
English Nature. 2004. Coastal Habitat Management Plans: An Interim Guide to Content and Structure. Available to download at http://
www.english-nature.org.uk/livingwiththesea/champs/default.asp
English Nature. 2005. England’s Best Wildlife and Geological Sites: The Condition of Sites of Special Scientific Interest in England in 2003.
Available to download at http://www.english-nature.org.uk/pubs/publication/PDF/SSSICondfulldoc.pdf
Environment Agency. 2005. Beach and Bathymetric Monitoring Programme. Shoreline Management Group, Anglian Region. Available to
download at http//www.environment-agency.gov.uk/regions/anglian
Evans E, Ashley R, Hall J, Penning-Rowsell E, Saul A, Sayers P, Thorne C, Watkinson A. 2004. Foresight. Future Flooding. Scientific
Summary: Vol. 1 – Future Risks and their Drivers. Office of Science and Technology: London.
Galvin CJ Jr. 1983. Sea-level rise and shoreline recession. Coastal Zone ’83, Vol. 3. American Society of Civil Engineers: New York; 2684–
2705.
Halcrow. 1980. Coast Protection Act 1949, Pebbleridge, Westward Ho! Report to Torridge District Council.
Houghton JT, Meira Filho LG, Callander BA, Harris N, Kattenberg A, Maskell K (eds). 1996. Climate Change 1995: The Science of Climate
Change. Cambridge University Press: Cambridge.
HR Wallingford. 2002. South North Sea Sediment Study: Sediment Transport. Report EX4526.
Huggett D. 1996. Developing a no net loss policy for coastal wetlands. Proceedings of 31st MAFF Conference of River & Coastal Engineers.
Annual Conference organised by Ministry of Agriculture, Fisheries and Food.
Copyright © 2006 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms 31, 1625–1642 (2006)
DOI: 10.1002/esp
UK coastal habitat future
1641
Hulme M, Jenkins GJ, Lu X, Turnpenny JR, Mitchell TD, Jones RG, Lowe J, Murphy JM, Hassell D, Boorman P, McDonald R, Hill S.
2002. Climate Change Scenarios for the United Kingdom: The UKCIP02 Scientific Report. Tyndall Centre for Climate Change Research,
School of Environmental Sciences, University of East Anglia: Norwich. Available to download at http://www.ukcip.org.uk/scenarios/
sci_report/sci_report.html
IPCC. 2001. Working Group I: The Scientific Basis: Ch.11.5 Future Sea Level Changes. Intergovernmental Panel on Climate Change, Third
Assessment Report. Available to download at http://www.grida.no/climate/ipcc_tar/wg1/429.htm
Jennings SC, Orford JD, Canti M, Devoy RJN, Straker V. 1998. The role of relative sea-level rise and changing sediment supply on
Holocene gravel barrier development; the example of Porlock, Somerset, UK. The Holocene 8: 165–181.
Jeuken MCJL, Wang ZB, Keiller D, Townend IH, Like GA. 2003. Morphological response of estuaries to nodal tide variation. International
Conference on Estuaries and Coasts (ICEC-2003). International Research Training Centre for Erosion and Sedimentation: Beijing; 167–
173.
JNCC. 2004. The Habitats Directive: Selection of Special Areas of Conservation in the UK. Joint Nature Conservation Council: Peterborough. Available to download at http://www.jncc.gov.uk/ProtectedSites/SACselection/default.htm
Keane P. 1997. Westward Ho! Against the Sea. Thematic Trails. School of Social Sciences, Oxford Brookes University.
Komar PD. 1998. Beach Processes and Sedimentation (second edition). Prentice Hall: Harlow.
Lee G, Nicholls RJ, Birkemeier WA. 1998. Storm-driven variability of the beach-nearshore profile at Duck, North Carolina, USA, 1981–
1991. Marine Geology 148: 163–177.
Lee ME. 2001a. Coastal defence and the Habitats Directive: Predictions of habitat change in Englad and Wales. Geographical Journal 167:
39–56.
Lee ME. 2001b. Estuaries and Coasts: morphological adjustments and process domains. In Geomorphological Processes and Landscape
Change: Britain in the Last 1000 Years, Higgitt DL, Lee ME (eds). Blackwell: London; 147–189.
Leggett DJ, Cooper N, Harvey R. 2004. Coastal and Estuarine Managed Realignment – Design Issues. Report C628. CIRIA: London.
Lonsdale KG, Downing TE, Nicholls RJ, Parker D, Vafeidis AT, Dawson R, Hall J. (in press). Plausible responses to the threat of rapid sealevel rise for the Thames estuary. Climate Change.
Lozano I, Devoy RNJ, May W, Andersen U. 2004. Storminess and vulnerability along the Atlantic coastlines of Europe: analysis of storm
records and of a greenhouse gases induced climate scenario. Marine Geology 210: 205–226.
May VJ. 2003. Westward Ho! cobble beach, Devon (SS440310). In Coastal Geomorphology of Great Britain, May VJ, Hansom JD (eds).
Geological Conservation Review Series, No 28. Joint Nature Conservation Committee: Peterborough; 238–241.
Metcalfe SE, Ellis S, Horton BP, Innes JB, McArthur JJ, Mitlehner A, Parkes A, Pethick JS, Rees JG, Ridgway J, Rutherford MM, Shennan
I, Tooley MJ. 2000. The Holocene evolution of the Humber estuary: reconstructing change in a dynamic environment. In Holocene Land–
Ocean Interaction and Environmental Change around the Western North Sea Shennan I, Andrews JE (eds). Special Publication 166.
Geological Society: London; 97–118.
Natura. 2000. Process of designated special areas for bio-diversity purposes within the EU. Available to download from http://europa.eu.int/
comm/environment/nature/nature_conservation/eu_nature_legislation/habitats_directive/index_en.htm
Nicholls RJ, Lowe JA. 2004. Benefits of mitigation of climate change for coastal areas. Global Climate Change 14: 229–244.
Orford JD. 2005. Coastal Environments. In Geomorphology for Engineers, Fookes PG, Lee EM, Milligan G (eds). CRC Press: Boca Raton;
576–602.
Orford JD, Carter RWG, McKenna J, Jennings SC. 1995a. The relationship between the rate of mesoscale sea-level rise and the retreat rate
of swash-aligned gravel-dominated coastal barriers. Marine Geology 124: 177–186.
Orford JD, Carter RWG, Jennings SC, Hinton AC. 1995b. Processes and timescales by which a coastal gravel-dominated barrier responds
geomorphologically to sea-level rise: Story Head barrier, Nova Scotia. Earth Surface Processes and Landforms 20: 21–37.
Orford JD, Carter RWG, Jennings SC. 1996. Control domains and morphological phases in gravel-dominated coastal barriers. Journal of
Coastal Research 12: 589–605.
Orford JD, Jennings SC, Forbes DL. 2001. Origin, development, reworking and breakdown of gravel-dominated coastal barriers in Atlantic
Canada: future scenarios for the British coast. In Ecology and Geomorphology of Coastal Shingles, Packham JR et al. (ed.). Westbury
Scientific Publications: UK; 23–55.
Pethick JS. 1991. Salt marsh geomorphology. In Salt Marshes, Allen JRL, Pye K (eds). Cambridge University Press: Cambridge; 41–
62.
Pethick JS. 1996. Mudflat geomorphology. In Estuarine Shorelines, Geomorphological and Ecological Interactions, Nordstrom K, Roman C
(eds). Wiley: Chichester; 184–211.
Pethick J, Orford JD, Young R. 2003. Allt Wen a Traeth, Tan-y-bwlch SSSI and Aberystwyth Frontage Nature Conservation Strategy. Report
for Countryside Council for Wales and Ceredigion County Council.
Posford Haskoning. 2002a. Essex Coastal Habitat Management Plan. In Living with the Sea. English Nature, Environment Agency, Defra,
NERC (CD format).
Posford Haskoning. 2002b. Dungeness and Pett Level. Coastal Habitat Management Plan. In Living with the Sea. English Nature, Environment Agency, Defra, NERC (CD format).
Posford Haskoning. 2003. Winterton Dunes. Coastal Habitat Management Plan. In Living with the Sea. English Nature, Environment
Agency, Defra, NERC (CD format).
Shennan I, Horton BP. 2002. Holocene land- and sea-level changes in Great Britain. Journal of Quaternary Science 17: 511–526.
Stapleton C, Pethick J. 1996. The Fal Estuary: Coastal Processes and Conservation. Report for English Nature. Institute of Estuarine and
Coastal Studies, University of Hull.
Copyright © 2006 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms 31, 1625–1642 (2006)
DOI: 10.1002/esp
1642
J. D. Orford and J. Pethick
Thomalla F, Vincent C, Black K. 2001. The effects of the segmented shore-parallel breakwaters at Sea Palling on the longshore transport of
sand. 36th Annual Conference of River and Coastal Engineers. Defra: London; 07.2.1–07.2.11
Townend I. 2005. An examination of empirical stability relationships for UK estuaries. Journal of Coastal Research 21: 1042–1053.
Townend I, Pethick J. 2003. Estuarine flooding and managed retreat. Philosophical Transactions of the Royal Society, London, A 360: 1477–
1495.
Van der Wal D, Pye K, Neal A. 2002. Long-term morphological change in the Ribble Estuary, northwest England. Marine Geology 189:
247–264.
Velegrakis AF, Gao S, Lafite R, Duppont JP, Hualt MF, Nash L, Collins MB. 1997. Resuspension and advection processes affecting
suspended particulate matter concentrations in the central English Channel. Journal of Sea Research 38: 17–34.
Copyright © 2006 John Wiley & Sons, Ltd.
Earth Surf. Process. Landforms 31, 1625–1642 (2006)
DOI: 10.1002/esp