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Annex 07: Cley-Salthouse managed
realignment
Note: This report was originally produced as part of the review
of coastal habitat restoration undertaken for the 'Living with the Sea' project.
It is also included here, within the shingle guide, because of the relevance
to many of the issues discussed for this habitat.
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The lagoons and coastal grazing marsh looking towards
the village of Cley, September 2001 |
Site Name: - Cley-Salthouse
Location
Introduction
Cley lies towards the eastern end of the North Norfolk
coast CHaMP. It consists of a shingle ridge with an area of coastal grazing
marsh, reedbeds, and an unusual transition to landward
from saline lagoons, through brackish habitats to freshwater. It is a candidate
Special Area of Conservation, a Special Protection Area and most of the coast
is designated as a Site of Special Scientific Interest. The shingle ridge provides
the main line of defence and has been maintained by the Environment Agency who
‘push-up’ material from both the beach and the landward side to
increase the height of the ridge. This operation is perceived to have reduced
the flood risk to the wildlife habitats, the villages of Cley
and Salthouse and a main road. Due to a decrease in the availability
of beach material, partly resulting from this intervention, this management
approach was considered to be largely unsustainable. As a result a sea defence
scheme was devised to construct a secondary line of defence and to restore the
shingle ridge to a more natural and effective profile. The scheme relied on
attempting to preserve the habitats in situ. However, it has been argued this
not only runs counter to natural processes, but may have led to a scheme being
proposed that was potentially damaging to the nature conservation interests
in the area (Murby 2002). Following a review of the scheme and discussions with
the European Commission it has been de-coupled from the “Living with the
Seas” project.
‘Protecting’ the coast at Cley-Salthouse
The shingle ridge running from Salthouse to Blakeney
Point lies along a highly dynamic coastline and provides a sea defence for much
of the land behind. The beach is now effectively ‘swash’ aligned
with relatively little east to west longshore transport and little nourishment by cliff erosion
further west. Sea level rise and storms cause the ridge to slowly migrate and
move landwards at the same time. Average rates of roll-over are approximately
1metre per year. Substantial damage to the ridge (as a flood defence structure)
tends to take place irregularly during storms, which cause over-washing of the
ridge and can lead to flooding of the land behind. The threat of overtopping
and flooding not only of land, but also of properties at Cley
and Salthouse led to the Environment Agency carrying
out sea defence works. In particular they have reprofiled
the shingle bank along the frontage here for 20 years or so (Figure North Norfolk
01).
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Figure North Norfolk 01, Cley-Salthouse, general situation in relation
to the shingle ridge, sand dunes and sand flats (appearing yellow on the satellite
image) and the location of beach reprofiling.
The process of reprofiling and occasional beach nourishment
has been undertaken in order to attempt to arrest the process of shingle roll-over
and increase flood protection. However despite these efforts in the last decade
or so the area has seen increased periods of storminess, with storm surges and
serious breaches of the shingle barrier occurring in 1993, 1996 and 1998. This
had led to this site being included in the “Living with the Sea”
project particularly highlighting the problems associated with ‘coastal
squeeze’ (see the Executive Summary of the North
Norfolk CHaMP).
The coastal squeeze - is it natural
change?
The situation at Cley-Salthouse provides an unusual example of the coastal
squeeze best viewed as natural habitat evolution. The combination
of sea level rise, increased storm and wave attack pushes the coastline landward
and the habitats lying behind the shingle bank are overwhelmed by the migrating
beach. Progressively lagoons and saltmarshes migrate landward reducing the area
of coastal grazing marsh and reedbed (Figure North Norfolk 02 below). For some
habitats, such as lagoons, tidal saltmarsh and the shingle bank itself these
will be reformed. Coastal grazing marshes will not. In the fullness of time,
however, (possibly several hundred years) the sequence of existing habitats
could disappear altogether, as the hinterland (including farmland and the villages
of Blakeney, Cley and Salthouse) lie mostly on rising ground. This is viewed
as natural habitat evolution and does not require compensation under the Habitats
Directive as a plan or project.
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Figure North Norfolk 02. Stylised figure showing the possible direction
of movement of Blakeney Point and spit over a prolonged period of sea level
rise and the influence of storms.
Saline intrusion - impact on reedbeds
Even with the efforts to limit erosion and inundation overtopping still takes
place periodically. The two most recent flooding events took place at Easter
and the seawater took up to two weeks to drain off the marsh. This caused the
temporary inundation of reedbed and affected the fortunes
of some breeding birds during that breeding season. This may be an important
consideration in the management and restoration of reedbeds (see the guide “Coastal
Habitat Restoration, towards good practice”).
‘Futurecoast’, coastal evolution
at Cley-Salthouse
The conclusions from the Futurecoast
review of the likely evolution of this section of coast largely confirm the
effects of ‘coastal squeeze’, namely:
“As well as growing westwards (towards Blakeney
Spit), the gravel ridge also shifted inland at an average rate of 1m per year
in the nineteenth century. The eastern end of the spit is
also realigning to keep pace with cliff retreat at Weybourne, although retreat of the chalk base of the cliff
is slow, much less than 1m per year. In an unconstrained situation, the shingle
barrier between Cley and Weybourne
would be expected to roll landwards towards a position commensurate with the
natural energy environment. It is likely that a lower barrier would form and
that this would be susceptible to occasional breaching and flooding of the low-lying
hinterland. Given that it is already seaward of its natural position, initial
rollback of the shingle ridge between Cley and Weybourne
could result in some breakdown of the barrier. This could eventually leave Blakeney
Spit as a barrier island. The predominantly freshwater marshes of Cley
would see a transition to saline lagoon and saltmarsh habitats.
The practice of attempting to build up the bank at its present position will
not succeed in stopping the bank from upper beach failure: the only way the
barrier will stabilise is when overwashing is allowed
to continue such that the barrier rolls onshore to form a wider stable position,
although the final crest height will probably be lower than the previously maintained
crest-height and frequency of inundation likely to increase. Consequently, with
continuance of recent practices, eventual catastrophic failure of an artificially
over-steepened shingle bank during storm events is probable.”
The Cley-Salthouse realignment scheme
In response to the continuing problems associated with breaching of the shingle
ridge, coastal squeeze and the effect of flooding on the plant and animal communities
of the grazing marsh and reedbeds consideration has
been given to a managed realignment scheme. This scheme was proposed as a means
of reconciling a number of the key issues highlighted above, namely:
- long-term ‘preservation’ of the site and its sequence of habitat
as ‘coastal squeeze’ takes place;
- increased risk of flooding affecting existing wildlife habitats
and property;
- reduction in speed of flood water runoff with
consequences again for existing wildlife habitats and property;
The University of Cambridge Coastal Research Unit investigated the situation
and future management options under contract to the Environment Agency (Cambridge
Coastal Research Unit 1997). It concluded that a ‘do-nothing’ option
would result in the shingle bank eventually blocking drainage from the marshes,
causing brackish lagoons to form. This would have far reaching effects on the
area’s animal and plant life, as well as on sediment transport along adjacent
coastal systems.
Alternative suggestions included two forms of managed realignment involving:
- re-routing drainage in the area, leaving the shingle to continue to move
landwards;
- construction of a secondary defensive
wall behind the shingle ridge.
The scheme
The North Norfolk Shoreline Management Plan (SMP) concluded that the existing
shingle ridge, which provides flood defence, is unsustainable. Although the
ridge had been successfully maintained for many years the reduction in the availability
of suitable material made this more and more difficult. The Environment Agency
investigated alternative options for flood protection and concluded that a partial
setback embankment was the most appropriate solution based on the second of
the two options above (Figure North Norfolk 03 below).
Figure North Norfolk 03. Proposed managed realignment at Cley-Salthouse.
This scheme is a compromise allowing the shingle ridge to move landwards whilst
at the same time providing a flood defence embankment.
The combination of wildlife interests, notably the Norfolk Wildlife Trust,
which owns a large area of the coastal grassing marsh and reedbed and those
living in properties subject to periodic flooding,
were in favour of the scheme. Other land owners and farmers who used the area
for cattle grazing were less convinced that any changes were needed. An application
by the Environment Agency for the construction of the bank was submitted to
North Norfolk District Council in June 1999 and approved, in principle, at a
meeting of the Planning and Highways (Regulatory) Committee in January 2000.
North Norfolk District Council approved the proposal at a meeting in March 2000.
Implications
The environmental impact assessment, which accompanied the application, suggested
that there would be a change in status of the habitats. In summary this would
cause:
“a loss of grazing marsh, reedbed, open water and
saltmarsh through the footprint of the embankment and its associated ‘topping
up’ reserve. South of the bank 80% of the grazing marsh, 40% of open water
and 90% of reedbed will become increasingly fresh due to a reduction in saline
inundation. Approximately 36 ha of saltmarsh south of the embankment will revert
back to freshwater grazing marsh. The proposed adjacent borrow pits, if granted
planning permission, would lead to the creation of a further approximately 14
ha of reedbed and the lowering and subsequent improvement of approximately 12
ha of reedbed. Approximately 12 ha of additional lagoons will also be created
north of the embankment, but the extent of this will reduce over time as the
shingle bank migrates landwards.” Taken from the Report by the Director of Planning and Transportation
to North Norfolk District in relation to the application P.01/99/0800,
Cley and Salthouse: Construction
of Clay Embankment, Outfall Structures, Drainage and Highway Works to Form Flood
Protection Scheme, for the Environment Agency.
In addition the scheme included the re-creation of a more natural, i.e. lower,
crest height for the shingle ridge. This would then, in the absence of maintenance,
allow new shingle plant communities to become re-established helping to extend
this important community within the candidate Special Area of Conservation.
The conservation view
The conservation position at the time suggested that the changes brought about
by the scheme would result in enhancement of inter-tidal interests but at the
expense of the freshwater interest, including some change to the bird interest.
This had important implications for both the marine candidate Special Areas
of Conservation and the Special Protection Area. Despite this the consensus
view of the conservation bodies was that the only option in the short to medium
term, which would protect the overall interest of the site, was to allow the
area (including the shingle bank) to develop in a more natural way, i.e. with
a lower more natural profile and without periodic reprofiling. This was a significant element in the proposal
as vegetated shingle is a rare habitat and its restoration a significant contribution
to the value of the candidate Special Areas of Conservation.
Building the clay embankment would preserve the freshwater habitats
(part of the SPA for birds including the bittern) allowing in the longer term
the possibility of creating freshwater sites elsewhere as compensation for the
areas lost. The new sea bank was also seen as having benefit for local residents,
although this was not a priority issue for English Nature.
The issues raised, not least those associated with complying with the EU Habitats
and Species Directive, led to the scheme being included with the LIFE Nature
funded ‘Living with the Seas’ project. Specifically as one of two
flood defence schemes within the North Norfolk Coast CHaMP (the other being
at Brancaster), for more information see the Guide
“Coastal Habitat Restoration, towards good
practice”.
Problems with the scheme
As details of the scheme unfolded it became clear that there were a number
of key issues that required further consideration, the report by the Director
of Planning and Transportation to North Norfolk District, for example,
identified several issues, which if not resolved could have resulted in a recommendation
that the application be refused, including:
- excavation of material for the embankment would require borrow
pits within the site, which would themselves require planning permission;
- it was clear that the work would have a significant impact
on the landscape and this needed to be considered;
- vehicle access and parking were also important and needed further consideration;
- the need for a clearly defined programme of monitoring;
- that the application should be explicit in terms of compensation
for habitat loss under the terms of the EU Habitats and Species Directive;
- public rights of way issues needed
to be resolved.
These problems were resolved and the full scheme was given approval. However,
it took over 5 years to complete the planning approvals and appropriate stakeholder
consultation. Even after the “Living with the Seas” project began,
in response to the requirements of the local community, interest groups and
local authorities the scheme continued to evolve. As a result of this the Environment
Agency and English Nature felt it was necessary to review the scheme to ensure
it still delivered the environmental and flood management requirements.
Reprofiling and beach nourishment -
impact on shingle vegetation
In keeping with other areas where reprofiling has
taken place the disturbance caused by the movement of shingle material (usually
by bulldozers) reduces or destroys any vegetation that has become established
on the shingle ridge surface. Continued disturbance prevents anything other
than ephemeral plants from becoming established. This is especially significant
in areas where the rare and specialist plants occur, such as those at Cley
where Glaucium flavum
only occurs in a few of the least disturbed places.
A secondary effect has also been recognised. In some instances reprofiling
has been accompanied by beach nourishment, such as took place during the
storms, which occurred early in 1996 (Bamber et al.
2001). A breach of the shingle bank led to its reconstruction, using heavy ‘earth’-moving
machinery. In addition to bulldozing the bank new material was added, which
was excavated from near to a number of lagoons and used to raise the height
of the ridge. Although the breach was closed, damage was caused to the shallow
lagoons both by movement of the machinery through them and by the excavation
of material. (For more information on this see the Saline Lagoon Guide, Bamber
et al. (2001). However that under a ‘natural’ regime with a shingle
ridge able to roll back saline lagoons would be ephemeral in their nature and
would gradually migrate landwards as opportunities allowed.
This incident illustrates a situation which all too easily occurs. In this
case it appears that the contractors were unaware of the significance of the
lagoons and some were severely reduced (lost) during this reconstruction, when
there may well have been opportunities to enhance these features as part of
the flood management works. Included in this guide are some general recommendations
on coastal
defence works, which can be given to construction workers.
Protection versus conservation - general
issues
Application of Regulations 48 and 49 are not interpreted by English Nature,
Environment Agency or DEFRA as creating a presumption
that habitats be preserved in their present location. However, habitats should
be conserved in situ where it is sustainable to do so. Where “no
alternatives” and “imperative reasons of over-riding public interest”
are demonstrated, providing compensatory habitat is an acceptable alternative
when promoting schemes, which may compromise existing features.
Comment: For shingle habitats a reliance on a ‘static’
approach to conservation may be counter productive for a habitat existing in
such a dynamic environment. The natural tendency for movement both alongshore
and inland not only have implications for the management and restoration of
beaches and areas of vegetated shingle, but also associated habitats such as
lagoons and saltmarshes. Natural movements of shingle in response to storms
will be seen as being part of the “natural structure and function”
of the system and is likely to be part of a conservation requirement to restore
this natural dynamic! This leads to a series of questions, which can be posed
in relation to ‘conserving’ or ‘preserving’ habitats,
namely:
- Should site boundaries be flexible or tightly defined?
- How can we assess the value of replacement of one habitat by another?
- How favourable conservation status relates to
site integrity?
- How to involve the local community in decision-making.
Comment: A further issue arises where ‘natural’ processes
result in habitat loss, for example through ‘natural evolution’
as is the case at Cley-Salthouse. Where these form part of a candidate Special
Area of Conservation or Special Protection Area is it appropriate to ‘let
nature take its course’? In this situation it is felt important that the
site is allowed to develop naturally, accepting that it will gradually diminish
in size. Issues of favourable conservation status for these features will need
to be considered at a national or even a European level.
Natural roll-over Cley-Salthouse
It is clear from the above discussion that a key consideration at Cley-Salthouse
is the extent to which habitats of European interest can be maintained in a
Favourable Conservation Status. Initially it was felt that the original scheme,
whilst causing some overall loss, provided for the restoration of one element
of interest (vegetated shingle) and either reduced risk to, or replacement of
others (reedbed and lagoon), was acceptable. As indicated
above ‘doing nothing’ would result in some losses anyway as the
shingle beach moves inland in response to rising sea level and storms.
Despite this earlier view, given that the original scheme has been reassessed,
it is appropriate to consider whether a wholly non-interventionist strategy
is acceptable. Given the dynamic nature of the coast, and the importance attached
to structure and function in identifying candidate Special Areas of Conservation,
it is arguable that non-intervention (or at least limited intervention) is the
most appropriate option in such situations.
Reedbed
Though not directly related to this issue the potential value of sea water
inundation as a means of controlling reed growth should not be overlooked. Growth
and colonisation of reedbed is relatively rapid and as a pioneer community it
can soon become overgrown so that the original reasons for recognising it as
an important habitat (for some specialist birds and invertebrates) may be compromised.
In these circumstances extensive management (by cutting, burning and other means
of arresting its succession) may be required to maintain the existing interest.
Periodic inundation by seawater may be a much more cost effective option! For
more detailed consideration of this issue see the Guide “Coastal Habitat
Restoration, towards good practice”.
Appraisal
The Environment Agency and English Nature were both actively engaged in trying
to seek the best “on-the-ground” solution for both the Natura 2000
and flood management needs of this site. Early scheme negotiations were protracted,
largely because of the changing context in which the scheme was appraised. What
was subsequently put forward had evolved significantly in form and cost from
the original proposal. Further time was required while the revised scheme was
finalised and submitted to the Department of Environment, Food and Rural Affairs
for grant-in-aid. These negotiations took most of a year with the result that
any works eventually approved would not be constructed for several years, certainly
not within the LIFE Project programme.
This review led to the scheme being de-coupled from the LIFE project.
The further discussions between the contracting parties (the Department of
Environment, Food and Rural Affairs ; the Environment Agency; English Nature)
and a review of the final scheme in the light of current thinking on sustainability,
found that it was no longer considered ‘best value’. Justification
for DEFRA funding of the scheme was based on the essential flood management
requirements for the Natura 2000 and Ramsar site interests. It became apparent
that there were alternative scheme options, delivering similar environmental
benefits (including conservation of Bitterns), in a more sustainable and cost-effective
way.
The table below provides a summary of the implications of adopting each of
the five shoreline policy options.
| Option |
Potential change - outcome |
Comment |
| No active intervention - Do Nothing |
Landward movement of shingle ridge; improvement of vegetated
shingle habitat; increase or at least no net loss saltmarsh; increase
of saline lagoons; overall loss of coastal grazing marsh; possible reduction
in area of reedbed; greater incidence of flooding houses and access roads;
changes to longshore drift. |
There is certain to be change in the existing range of
habitats over time as the shingle ridge moves landwards against a rising
land level. The vegetated shingle habitat is almost certain to improve
as a more natural profile develops. Similarly it is likely that saline
lagoons (a priority habitat under the ‘Habitats’ Directive)
will also increase in area and status. |
| Advance the Line |
Requires accretion of beach and extension of saltmarsh
and other habitats as the shingle spit moves seaward. |
Require a major input of new material to the beach or offshore
breakwater - not a feasible alternative |
| Hold the Line |
The most recent policy. Continued loss of vegetated shingle
habitat, possible damage or loss of coastal lagoons (priority habitat).
Increased inundation and damage to reedbed. Overall artificial maintenance
of the existing habitats is possible. |
In the medium to long term, without major input of new
shingle material from cliff erosion or imported from offshore, this approach
is unsustainable. |
| Limited Intervention |
As for the ‘do nothing’ policy but with a retarded
rate of change. See modified scheme below. |
This policy could include several options such as protecting
the houses from flooding by some form of sea defence close to the houses.
Improvement of drainage from the grazing marsh and reedbed to offset overtopping. |
| Managed realignment |
Enhancement of marine interests but at the expense of the
freshwater interest, including some change to the bird interest |
The original scheme: costly and possibly not fulfilling
the original aim of the approach (see above) |
The modified scheme
In light of this further consideration, the
scheme has been modified to one involving ‘limited intervention’.
The shingle ridge will be reprofiled to re-create
a natural, more robust profile that will be able to support the shingle vegetation
features of the cSAC. It is anticipated there will be less chance of the shingle
ridge breaching (or a reduced risk of catastrophic failure). The lower crest
height may mean an increase in overtopping, allowing the fresh water/saline
gradient from the landward to the sea and its interesting ecology to be maintained.
Sluices are planned allowing quicker evacuation of water from the reedbeds,
fields and lagoons following any tidal inundation. It potentially also involves
localised flood risk management at Salthouse village. Over time there will be evolution of the
ecology of the wetland as it adjusts to the increasing saline conditions; this
is viewed as ‘natural change’. This current scheme proposal has
yet to be finalised and approved but is now considered to represent a more sustainable
and cost-effective option. The basic difference
being a gradual reduction in the overall area of grazing marsh and reedbed
and long-term changes to its salinity.
It should be noted that this re-assessment is made on the basis of a proposed
flood defence scheme (November 2002) and therefore the predicted habitat changes
represent a preliminary estimation that could be subject to change. It is considered
appropriate to consider this as habitat evolution rather than as loss or gain
of specific habitat types. Note the long term realignment and development of
a more natural coastline is one of a number of recommendations made in this
CHaMP. This conclusion may suggest a more general review of specific proposals,
such as the Cley-Salthouse realignment, should be
taken against this wider perspective.
Lessons learnt
The Cley-Salthouse case study provides important insights into several issues.
These relate not only to the nature conservation implications of adopting a
particular policy but also to procedural considerations when dealing with complex
and innovative approaches to habitat restoration. Three key areas have been
identified:
- the use of engineered approaches implicit in managed realignment and holding
the line;
- the problems with schemes, which require the creation of one habitat and
the displacement of another;
- delays in processing the scheme
including problems associated with landscape and public access considerations,
which may not be a significant component of the nature conservation case,
but important in relation to planning.
Taking each of these in turn some important lessons can be gleaned, which will
help consideration of these issues in other similar schemes.
Managed realignment
Historically the approach to the protection of land, property and life has
been viewed as a ‘battle with the sea’. In the face of rising sea
levels, increasing storm frequency and severity the traditional response is
to raise and strengthen the defences. Because it is based on tried and tested
technologies there is a degree of certainty about the level of protection that
is provided (although this is not supported by experience). By contrast, ‘letting
nature take its course’ may appear to be fraught with uncertainty or even
danger. Yet if the natural world, especially dynamic coastal habitats, is viewed
from a different perspective then the dangers may be more apparent than real.
In recent years there has been increasing recognition of the value of ‘natural’
habitats for coastal defence. This has been most clearly expressed in relation
to saltmarshes, which are key components in the justification for many realignment
sites, especially in Essex. By helping to buffer the effects of waves against
sea walls they can help improve the overall sea defence capability, whilst at
the same time reducing costs.
With the better understanding of the evolution of
the coastline (derived from coastal geomorphological studies) has come
greater recognition that the traditional approach to coastal defence is
not sustainable. The revised scheme at Cley-Salthouse, which involves
a policy of ‘limited intervention’, is considered to be more
sustainable in the long term. This conclusion suggests such an approach
may be more readily applied and in a wider variety of situations, than
the traditional view of coastal defence might suggest. |
Creating one habitat and displacing
another
A key factor in the design of the original scheme appears to have been the
fact that it represented the best means of maintaining the ‘status quo’
for the majority of nature conservation interests. At the same time it had the
added advantage of helping to restore a more natural profile to the shingle
ridge and with it the restoration of shingle vegetation.
However, both the original and revised schemes involve some ‘trade-off’
between existing and restored habitat. The fact that the revised scheme represents
a greater departure from the ‘status quo’ than the original scheme,
and is a move towards restoring the ecological form and function of the site,
is an important step forward. In this case the resultant habitat restoration
will not necessarily be on a ‘like for like’ basis. This is particularly
important in the context of creating reedbed suitable for bitterns, which may
well be displaced from this site.
| Maintaining ‘favourable condition’ of an
individual habitat or species can be met by a combination of restoring ecological
form and function, re-creation of habitats elsewhere or in some cases protection
‘in situ’. Whilst the former is preferred the latter two may
be an acceptable part of a balanced approach, especially where dynamic coastal
systems are involved, such as those occurring at Cley-Salthouse. |
Progressing a scheme
Another valuable experience from both the Brancaster and Cley-Salthouse schemes has been gained in the
design and approval stages, where the unique nature of the combined habitat
creation/flood defence schemes has raised important learning points for the
UK partners. At Cley-Salthouse in particular the issues were complex and there
were many unforeseen planning and other conditions that delayed the implementation
of the scheme. These combined with the need to engage the local population are
significant elements in any restoration scheme especially where new or innovative
approaches are being considered.
| Great attention must be paid at the outset when contemplating
habitat restoration, not only to the demands relating to nature conservation
issues, but also those involving local socio-economic and planning considerations. |
References
Bamber,
R.N., Gilliland, P.M. & Shardlow, E.A., 2001. Saline Lagoons: a Guide to their
Management and Creation (Interim Version), Saline Lagoon Working Group, Report
to English Nature
Cambridge Coastal Research Unit, 1997. North Norfolk
Sea Defence: Cley-Kelling Environmental Investigation.
Coastal Research Unit, University of Cambridge.
Murby 2002. Why do we pay so much to protect wildlife
from nature? Coastal Futures Conference, London, Coastal Management for
Sustainability, Kemply, Glos.
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