Information provided by North Norfolk District Council - www.northnorfolk.org/coastal
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The United Kingdom, as an island nation, has always had a close relationship with the sea and for centuries people have settled in coastal locations to take advantage of its flat land, resources and transport potential. Consequently, coastal defences and especially port facilities have also been constructed over the centuries, although these attempts have met with varying degrees of success.
The onset of the industrial revolution resulted in a much higher demand for the benefits of a coastal location; a demand exacerbated by society's new-found desire for coastal recreation. However, this development was increasingly threatened by the natural erosion and flooding processes of the coastal environment. To deal with the threat the new engineering technologies were used to create coastal defences, on a scale unseen before, to oppose the action of the sea and protect the assets behind. Coastal development has continued throughout the last century, resulting in a continual demand for defences to protect it.
Coastal defences, by their very nature, disrupt the natural processes operating on the coastline but early knowledge of these processes was somewhat limited. Indeed, it was not until the Normandy invasion, during the Second World War, that a detailed knowledge of physical coastal processes was required and this initial research provided the impetus for the detailed investigation that continues today.
The time lag between widespread construction of coastal defences and the detailed understanding of coastal processes meant that defences were often constructed in what would prove to be inappropriate manners or locations. Unfortunately, by the time this was realised so much development had occurred that defences had to be maintained, even if they were causing further problems.
In 1949 the Coast Protection Act provided legislation that gave a Coast Protection Authority the power to carry out whatever work they deemed necessary for the protection of any land in their area. In North Norfolk responsibility for coast protection was with the Urban and Rural District Councils of Wells, Walsingham, Sheringham, Erpingham, Cromer and Smallburgh. The approach of each council towards coast protection differed, particularly in respect of financial commitments towards the works. There was no long term policy for coastal management and work was generally carried out on a yearly basis, by consultant civil engineering practices retained by the councils (particularly 'Mobbs and English' and 'Lewis and Duvivier'). This split responsibility was one of the main reasons for the range of defence structures and particularly groyne types that can be seen on the North Norfolk coast.
In 1974, North Norfolk District Council was formed and assumed the coast protection responsibilities of the former Urban and Rural Councils. The new Council became the Coast Protection Authority and was committed to protecting the coastline within its area and principally used 'Mobbs and English' as consultant civil engineers to advise on and undertake coast protection matters.
In the late 80's NNDC's Technical Services department began to take a slightly more active role in coast protection and they took full responsibility in 1989 when the Mobbs and English consultancy closed due to the demise of its Senior partner. Technical Services decided that the way forward in the District was to study the whole of the coastline and evolve a coherent policy for future coast protection works. The coastline was split into management units, discrete lengths of coast possessing some commonalty in their geology, land use, or coastal defence. The defence requirements of each unit could be identified and prioritised, allowing engineering efforts to concentrate on those areas with greatest need. In 1990, NNDC published a strategy for the integrated management of its frontage and this represented one of the first examples of this type of approach.
In 1993 the Ministry of Agriculture, Fisheries and Food, who had overall policy responsibility for flood defence and coast protection in England, published their 'Strategy for Flood and Coastal Defence' which set out national policy. They also produced a number of other guidance documents. At the forefront of their approach was a move towards strategic thinking and recognition that coastal processes ignore the administrative boundaries that we impose on ourselves.
To enable a more appropriate approach to be taken, research was commissioned which identified Sediment cells and sub-cells. These cells represent more or less discrete lengths of coastline for the purposes of sediment transport and were chosen as appropriate units for the development of Shoreline Management Plans.
Shoreline Management Plans (SMPs) are produced through co-operation between all relevant Coast Protection Authorities and the Environment Agency (who provide sea defences to prevent coastal flooding in England and Wales). Each SMP sets out generic policies for the management of the coastline and the document forms the top level in a heiracy of plans and studies intended to ensure all new coastal defence works are constructed to work with, rather than against, natural processes. This is explained more clearly in Document 3.
MAFF also encouraged the formation of the Coastal Groups, which began in the late 1980's. These bodies ensure authorities communicate with their neighbours and are aware of issues outside of their administrative area.
North Norfolk is a member of the Anglian Coastal Authorities Group (ACAG) which stretches from the Wash round to the Thames. Its main membership includes Local Authorities with a coast protection responsibility, the Environment Agency, DEFRA (formerly MAFF) and English Nature. Other bodies, such as environmental groups, are included within the relevant sub-groups (one for each sub-cell).
In 1999 most of NNDC's Technical Services unit was transferred to the County Council, but 3 staff were retained and now form the Coastal Management Unit which ensures the council continues to provide its coast protection function.
Throughout the 1990's and 2000/01 MAFF continued to develop their strategic approach towards coastal defence and have recently released a new set of guidance documents. In June 2001 the Ministry of Agriculture, Fisheries and Food was replaced by the new Department for Environment, Food and Rural Affairs who have inherited all of MAFF's responsibilities for Flood and Coastal Defence. For more information visit the website at www.defra.gov.uk
Without doubt, the best defence against erosion, encroachment or inundation by the sea is a natural wide flat beach topped off at the inshore end with either high deep sand dunes or a shingle bank. These natural structures absorb the wave energy and offer protection to the hinterland be it flood plain or erodable cliff.
Where the beach and/or bank is unable to withstand storm conditions and either erosion or inundation threatens important assets then some form of artificial strengthening of the coastline may be desirable.
In North Norfolk this strengthening has taken many forms ranging from the construction of concrete seawalls to beach nourishment activity. A number of defence types are described below, although the list covers only those defences used by NNDC for coast protection works and is certainly not a comprehensive list of all possible defence types.
The seawalls built in North Norfolk take a variety of forms from the early mass concrete, vertical faced, walls as seen in Sheringham to the more highly designed modern wave reflecting walls similar to the one at Cart Gap.
Seawalls all have one thing in common, they are intended to reflect and/or refract all the wave energy away from the land behind. This wave energy manifests itself in various ways from a reflected return wave to general water turbulence. Unfortunately the reflected wave can, and often does, result in increased erosion or scour of the beach immediately in front of the sea wall. This erosion can be very detrimental and may result in the foundations of that wall becoming exposed by the eroding beach. If the erosion is allowed to continue unrestrained the seawall will become unstable and eventually collapse.
The ideal situation would be one where a large beach exists, with the sea only reaching the highest point of the beach during storm surge conditions. A seawall can then be provided at the top of the beach to act as the ultimate defence against flooding and erosion at times of high tide and surge. Providing the beach can be retained then the situation is stable.
In reality such a situation does not always exist and often seawalls will regularly be exposed to the action of the sea. In such circumstances the walls will need more frequent repair and maintenance work. If a good beach does not exist then supplementary defences are often required to protect the wall or maintain a beach.
Figure 1. A traditional type of seawall similar to that found at Cromer or Mundesley. The apron and steel piling has usually been added some time after original construction.
Figure 2. Sloping seawall design, such as that built at Bacton and Walcott around 1954.
Rock (Figures 3 & 4)
Rock or rock armour has become increasingly important in coastal defence works over the last 20 years or so. The rock used will typically be a very hard igneous rock that is exceedingly resistant to erosion. When rock is placed on the beach it is arranged so that large void spaces are left. When waves hit the rock they are only partially reflected, and can flow round the rocks, expending their energy less quickly which reduces scour. Another advantage of using rock is that if the rocks are moved during heavy storms it is a simple procedure to replace them in the correct position.
Rock armour is often used to protect the base of seawalls and prevents direct attack and damage of the wall. Additionally the rock provides support for the wall, improving its stability. Rock armour can also be used on its own either as a longitudinal defence (like a sea wall) known as Rip Rap or to construct groynes.
Importantly, because the rock needs to be resistant it is often very different to the material found naturally at a location. Consequently rock armour may look out of place and is not suitable for use in all locations.
Figure 3. Sheringham Beach. Both rock groynes and rock armour can clearly be seen.
Figure 4. This overhead of Sheringham (courtesy of the Environment Agency) shows the seawall, rock armour and both rock and timber groynes.
Timber Revetments were first constructed as cheaper alternative to a solid seawall. The Revetments are constructed from timber piles driven into the beach and connected by a sloping lattice of timber planks. Either a concrete apron or steel sheet piles are used to provide foundations for the structure and these are intended to remain below beach level.
The Revetment is designed so that it will break the force of the wave without reflecting the energy which might cause scouring of the beach. A Timber Revetment reduces the wave energy available to attack the cliffs but it does not prevent erosion from taking place. In addition, sediment, which can be sand, shingle or pebbles, is carried through or over the revetment structure by an incoming wave. However, the sediment cannot easily return seaward once the force of the wave has been dissipated. This action results in a build up of material behind the revetment and the increased depth of material protects the foot of the cliff from being attacked by the sea.
Timber Revetments are built at the top of the beach to absorb wave energy during high tide conditions because this is the only time waves can reach the base of the cliffs.
Unfortunately, if beach levels in front of a Timber Revetment drop then the steel piles or apron can become exposed. They then tend to act as a simple seawall (although the are not designed to do this) and reflect a large proportion of the wave energy, which can cause further erosion of the beach and ultimately the potential undermining and collapse of the Revetment.
Block Revetments (Figure 8)
Block revetments consist of a steel or timber framework that acts as containment for concrete or rock fill material. The block revetments act to dissipate wave energy without reflecting it and are very similar to Rip Rap. Block Revetments are fairly cheap to construct because they are often built from spare or scrap material; however they can be unsightly.
Figure 5. A sloping timber revetment, used widely on the North Norfolk coast.
Figure 6. Face on view of a timber revetment. Notice the steel sheet piles exposed at the foot of the structure.
Figure 7. This overhead (courtesy of the Environment Agency) shows the coast east of Overstrand. The timber revetment and groyne field are clearly displayed.
Figure 8. A block filled revetment similar to that found at Mundesley.
The purpose of a groyne is to create and maintain a healthy beach on its updrift side, which in turn provides protection to the land behind. This is achieved through two main processes.
Firstly, groynes act as a barrier to physically stop sediment transport (sand) in the direction of littoral drift through the system. This causes a build-up of the beach on the groyne's updrift side. Secondly, groynes interrupt the tidal flow forcing the tidal current further offshore beyond the groyne end. This slows the tidal current inshore causing the deposition of heavier sediments and encouraging the beach to grow in size.
In North Norfolk a range of different groyne designs exist that can be divided into two basic types - Impermeable and Permeable groynes.
As the name implies, impermeable groynes are solid and are designed to intercept all material arriving on the updrift side. This allows a large beach to develop and, if correctly designed, they do work extremely well. A good example of this is the groyne opposite the "Doctors Steps" at the east end of Cromer. The groyne is wooden with a concrete inshore end, and it holds a huge beach in front of the gangway from which the local fishing boats launch and retrieve.
Obviously, if a groyne is stopping material from moving along the coast then the down-drift side of the groyne will be starved of material (which is why it is usually lower than the up-drift side). If a groyne is correctly designed then there will be a limit to the amount of material it can hold and excess sediment is free to move on through the system. However, if a groyne is too large it may trap all sediment reaching it and this can cause severe beach erosion problems on the down-drift side, which in turn can result in cliff erosion problems.
In an attempt to prevent problems with down-drift starvation, a series of groynes were designed on the basis that they would be "permeable" and instead of trapping the total amount of sediment they would allow some to pass through. These groynes are generally known as "Erpinghams" (after the Rural District Council in which they were initially used). The vertical timbers are space approximately 40mm apart, giving a void ratio of between 10 and 20 percent. The groynes were apparently successful and have been used in a number of locations on the North Norfolk coast. Today it is unclear if these permeable groynes provide any benefit, but to find out it would be necessary to remove a groyne and see if the beach then disappeared.
The use of groynes in general is has its critics, because some people believe that any disruption of natural systems should be avoided. However, experience has shown that groynes can be effective in maintaining healthy beaches and consequently they form an important component of North Norfolk's defences.
Figure 9. A permeable timber groyne known as an "Erpingham".
Figure 10. An impermeable timber and steel sheet pile groyne
Figure 11. This photo shows the same permeable "Erpingham" groynes as Figure 7.
A beach is the perfect defence against wave action and, if a beach is poor, one option may be to undertake beach nourishment. This basically involves adding large quantities of material to a beach in order to build it up. The material added will need to be very similar to the material naturally found on the beach and will probably come from remote sources. Offshore dredging can provide a good source of suitable material for beach nourishment schemes or alternatively the sediment can be obtained from land based quarries. Beach management structures may also be necessary to ensure the extra material remains on the beach, and even so some will probably be lost through the natural movement of coastal sediments. This may mean further nourishment is required in the future to keep the beaches at the desired level.
Nine offshore breakwaters have been constructed by the Environment Agency to protect the coast around Sea Palling and for information on them it is necessary to contact the Agency. The purpose of the breakwaters is to prevent storm waves from reaching the beach and to alter the natural processes so that a wider beach is able to develop behind them.
In addition to the defences preventing waves from eroding the cliffs, there are also numerous structures that help prevent groundwater from causing erosion.
Gabions are generally galvanised steel wire mesh baskets filled with rock (often local flint in North Norfolk). The size of the basket vary but they are typically 2m x 1m x 1m and are rectangular cubes with a mesh size in the order of 20mm. Gabions are normally used on eroding cliff faces where their purpose is two fold. Firstly they provide stability to the cliff face, preventing failure, and secondly they permit water to drain away that might otherwise contribute to landsliding. Gabions are relatively cheap and easy to construct but they are not suitable for use in locations exposed to wave action because they are too flexible and are easily destroyed.
Cliff drains are often present on the cliff faces behind seawalls where they collect water from the cliffs and transport it through the seawall. This helps to reduce instability caused by water in the cliffs or trapped behind the seawall and also prevents gullying by intercepting surface water that would otherwise flow down the cliff face.
Boreholes are vertical shafts in the ground. In some places boreholes are used to access groundwater but in North Norfolk they are used to dispose of it. The boreholes are sunk down below sealevel into the chalk that underlies the whole area. Surface water and groundwater that is intercepted by the borehole is transported straight into the chalk which reduces the amount of water available to cause instability in the cliffs.
Appendix 1 provides some approximate values for the cost of constructing the different types of defence structures.
Appendix 2 presents a simple list of the defences in place on the North Norfolk coast.
Appendix 3 contains some design data for coast protection structures.
There are no coastal defences along this stretch of coast. The coastal strip is protected solely by the existence of the low cliffs with the shingle bank at their base.
A shingle bank, approximately 250m long, protects the low-lying coastal area to the rear from inundation by the sea. In an attempt to strengthen the bank a timber and steel palisade (breastwork) was buried within the bank to provide stability during storm conditions. The palisade has been exposed on several occasions and severely damaged by direct wave attack, which it was not designed to withstand. The presence of the palisade may have prevented the bank from breaching but it was also causing it to be heavily eroded by preventing it from behaving naturally. Today, most of the palisade has been removed and only a short length remains, often visible in the bank.
A shingle bank will provide the best defence if it is able to evolve naturally and gradually retreat inland. Therefore it has been decided that this will be allowed to happen at Weybourne. A consequence of this approach is that the car park may occasionally flood, and to prevent this flooding affecting the 6 properties behind the carpark, the Council intends to construct a small floodbank.
There are no defences along this stretch of coast. The coastal strip is backed by cliffs with a shingle bank at their base. The shingle foreshore is fed by gravel arising from the erosion of the cliffs as well as flints released from the chalk bedrock, which is exposed at low water.
Sheringham town frontage is protected by a seawall/promenade with a groynage system in front. Rock armour has been placed along the base of the seawall to provide protection against wave attack. The groynes at Sheringham include both wooden and rock structures. Numerous cliff drains are also present at Sheringham.
Document 7 covers the Sheringham defences in more detail.
The Sheringham seawall ends beneath Beeston Hill, at which point a timber revetment and groyne system, designed and constructed in 1976, runs eastwards to West Runton Gap. The SMP policy for this length of coast is one of 'Managed Retreat' and, in line with this policy, the revetment is no-longer being maintained. It is in a poor state of repair and has failed at many locations. Eventually the revetment will fail completely and should sections become hazardous to public safety they will be removed. The coastline will then be left to evolve naturally.
Apart from two small seawalls at East and West Runton there are no defences in this area. The seawalls maintain the access ramps to the beach and will be maintained to allow continued beach access
The main defences at Cromer were built between 1859 to 1900 and have been extensively repaired and extended since then. There is a wide, black topped, promenade at approximately 6.5m AOD running for the majority of the town frontage. This is backed by either graded vegetated cliffs or solid brick/stone walls approximately 15-30m high. From North Lodge Park eastwards the cliffs are no longer graded although cliff drainage is still present.
A strategy study has been commenced at Cromer to assess the condition of the defences and to determine appropriate management actions to ensure Cromer is adequately defended in the future.
The study has indicated that the seawalls are generally in reasonable condition although there is cause for concern at certain locations especially around the Pier Forecourt area. The groynes are generally of a solid design and many are showing signs of wear on the main piles and planks, especially the larger groynes to the east of the town. It is likely that, following the study, a scheme of remedial works will be justified and undertaken.
From east of Cromer to west of Overstrand the only defences in place are several timber groynes that have their inshore ends tucked into the cliffs to stop outflanking. In line with the SMP policy of 'Do Nothing', these groynes are not being maintained and will be allowed to fail.
At the western edge of Overstrand there is a length of timber revetment and a short section of block revetment before the start of the Seawall, promenade and groyne system that stretches eastwards for about 600 metres along the frontage. The defence then becomes a timber revetment once more.
The beaches at Overstrand are generally low, exposing the steel sheet piled foundations both the walls and the revetments. The defences in general are showing signs of ageing and it is expected that major repair works will be needed in the near future. To address this issue, the Council is undertaking a strategic study of the Overstrand frontage to identify where works are required.
Ground water percolating through the cliffs is a considerable problem at Overstrand and a number of cliff drains and boreholes exist to try to reduce the erosion this causes. The use of a gabion embankment behind the promenade and retaining wall has proved effective in stabilising one section of the cliffs.
Following a cliff failure at Clifton Way in the early 1990's, work was undertaken to stabilise the site. As a result, surface and sub-surface drains were constructed and a large amount of rock armour was used to hold the slip's 'toe' in place. This rock is clearly visible behind the revetment to the east of Overstrand and a separate document describes the works undertaken in much greater detail (Document 8).
A timber revetment and groynage system (extended eastward from Overstrand in 1986/87) runs east as far as Sidestrand. From Sidestrand on to Trimingham there are no defences present.
The defences start again at Trimingham in the form of a wooden revetment and Groyne system. The revetment design at Trimingham is different to that generally found elsewhere on the coast because it has a concrete apron to provide better foundations for the structure.
Unfortunately the revetment has been largely destroyed by landslides, which have punched straight through the timber frames. The beach levels at Trimingham have also dropped, exposing the apron, which in turn creates a scouring effect causing further erosion of the beach. The apron is currently acting as a seawall at Trimingham, but it was not designed to do this and is consequently being severely damaged. Many of the Groynes at Trimingham are also in a poor state of repair.
Trimingham's defences are beyond the point where they can be repaired and really new defences need to be constructed. The problem is that it is not possible to justify constructing new defences under DEFRA's criteria because there are not sufficient assets at risk.
There is a continuous line of revetment extending from Trimingham to Mundesley along with a permeable groyne system. The revetment is of the traditional design and lacks the concrete foundations seen at Trimingham. The revetment is reasonable condition, although at a couple of points landslides have destroyed it.
An access road runs down the cliffs at Vale Road, just outside Mundesley and this is the first access point since Overstrand where it is possible to get vehicles onto the beach. The lack of access causes significant difficulties for maintenance operations, as it is very difficult to get plant equipment to where it is needed.
At Mundesley, the end of the revetment running from Trimingham defends the western edge of the village. This then becomes a concrete block revetment for about 400 metres before the start of a seawall, with promenade, that runs along the remaining length of the village. Again there is a groyne system at Mundesley and at present it is holding a very good beach.
A continuous wooden revetment and groyne system stretches from Mundesley to Bacton and provides protection for the Natural Gas Terminal at Bacton.
The coastal cliffs drop in height at Bacton to only a few metres above the high tide mark and a concrete seawall starts at the end of the revetment, west of Cable Gap. The seawall consists of a low-level concrete apron backed by an inclined concrete face with a wave wall at the top at approximately 6.5m AOD. The seawall was constructed in 1952/54 and requires annual maintenance to keep it in a suitable condition. The Groyne field at Bacton was reconstructed about 10 years ago, and is generally in a good condition, although some work is required on the seaward ends of the groynes.
A timber revetment and Groyne system runs through to Happisburgh and the first 300 metres of this, from the end of the seawall, were reconstructed in 1995 and are in good conditon. The remainder of the revetment has been abandoned in line with SMP policy and is generally in a very poor condition or has failed completely.
Happisburgh provides NNDC with one of its biggest problem areas. Although most of the village is set well back from the cliff top, Beach Road runs out to the cliffs and properties here a situated right on the cliff edge.
Originally a wooden revetment stretched all the way through to the Cart Gap seawall but in 1990 a storm destroyed around 300 metres of revetment to the east of Happisburgh. This led to rapid erosion of the cliffs behind, which fortunately were only topped with agricultural land. The remaining revetment continued to be damaged by storms and in 1996 another length of revetment was lost. Again rapid cliff erosion followed and this time six clifftop properties were lost.
At present the remaining length of revetment is being maintained and protects the properties behind. However, each storm causes more damage to a defensive structure that has already outlived its design life. At the base of the cliff there is a combination of gabions/flexible concrete blocks/3" steel tubes banded together to lie in a breastwork - all enclosed by bullhead rail piles and timber bracing. This secondary defence is thought to offer little actual protection.
On two occasions following the initial loss of defences at Happisburgh, NNDC have tried to promote schemes to construct new defences but on both occasions it has not been possible to obtain approval. The Council has therefore undertaken a strategic study of the frontage using consultants HR Wallingford to look at the processes operating and the assets at risk to determine a management plan for the Happisburgh Frontage. Once completed the study will indicate if it is possible to provide any new protection for Beach Road, Happisburgh.
Cart Gap marks the end of NNDC's area of responsibility and the EA maintains the sea defences to the east. A seawall runs east towards Sea Palling and in 1986 this was extended west towards Happisburgh for 600 metres. The wall is in good condition with an excellent beach currently maintained in front of it.
A more comprehensive list of the defences present on the North Norfolk coast is provided in Document 9.
In order to maintain development in coastal locations we often find ourselves in conflict with natural processes, and without protective engineering works such development may well be lost. However, experience now shows us that simply constructing large defensive structures to directly oppose these processes is not an effective long-term solution because such defences require frequent maintenance and may cause their own problems.
In North Norfolk, for example, defences now protect the majority of the cliffed coastline, however the erosion of these cliffs provided the material on the beaches. By limiting erosion we prevent the creation of new beach material and currently see a trend of falling beach levels. As the beaches form the best defence against erosion it appears that the widespread construction of defences may, in the longer term, reduce rather than increase the protection afforded to the cliffs. To address this issue, the SMP identifies lengths of coast where defences will not be maintained and natural erosional processes will be allowed to operate to ensure there is a continued supply of sediment to the beaches.
The provision of coastal defences today is intended to ensure 'at risk' locations are adequately defended and that the defences used will be effective. In achieving this aim it is important to work with natural processes where possible to try and prevent adverse side effects. It is recognised that the whole coastline cannot be cased in concrete and that if defences are needed at one point, other locations should remain undefended to limit disruption to natural systems. Consequently a choice has been made that while the protection of property and life remain high priority, protecting agricultural land, for example, is less important and its loss may well be acceptable. The planning system must play an important role here to guide development away from locations at risk from flooding or erosion and reduce the demand for new defences.
Unfortunately, the situation is never simple because the demand for defences is largely driven by historic decisions on where to defend meaning the provision of defences is reactive rather than proactive. This may not be a problem in large settlements, where sufficient assets are present to justify defences economically. However, for small rural settlements or isolated properties there may be little or no economic justification for expensive coastal defence works. It is important to note at this point that both sea defence and coast protection works are provided under permissive powers. This means there is no statutory duty for defences to be provided against either flooding or erosion.
For the people affected this can be of immense significance, and more so for erosion problems than for flooding. If your house floods then although your possessions may be damaged, you still have the house and you should be able to get insurance. If your house is affected by erosion then, once it is lost, you have nothing. You cannot get insurance to cover erosion and you cannot get compensation for your loss.
It is, therefore, unsurprising that people tend to object when told their properties will not be protected because they do not meet Government criteria or because it is in the 'greater good' for the location to continue to erode. The situation becomes that much more difficult to deal with if the location has previously been defended when a different set of criteria were used to decide if defences should be built.
What is clear is that the current situation is not perfect and that changes do need to be made. People need to be educated to remove their perception that the coast should be defended at all costs, an idea which terminology such as 'coastal defence' 'and coast protection' tends to reinforce. It is equally important however to ensure social issues are addressed more effectively when assessing the need for coastal defences and if they are not to be provided then possibly the subject of compensation needs to be reconsidered.
Looking to the future, while our understanding and technical abilities may continue to improve, the problems will remain. Gradual erosion of cliffed coastlines, such as North Norfolk's, will continue and sea level rise predictions suggest low-lying land will continue to be at risk of inundation. As the coast continues to retreat it will inevitably bring inland settlements closer to the sea and thereby increase the demand for new defences. The future, therefore, may well see an increase in the lengths of defended coast at the expense of areas left for natural processes, unless some major changes are made in our approach to coastal development. More and bigger defences could be built, but can they be environmentally or economically justified? The alternative is to accept that not everywhere can be protected and that in some cases the abandonment of some settlements might be the best option. The question then becomes who would be prepared to make such a decision and would the public ever accept it?
What ever happens, the provision of coastal defences will continue to be a complex issue.
The following table provides the approximate lengths of coastline within each SMP Management Unit and brief details of the associated defences. A more detailed description of North Norfolk's defences is provided in Appendix 4. These distances are only approximate because they have been scaled off 1:10,000 maps and may ignore some of the curvature present in both the coast and its defences.
| Management Unit | Total Length (m) | Length of Seawall (m) | Length of Revetment (m) | Number of Groynes |
| Unit 1 | 5600 | |||
| RUN 1 | 1765 | 1610 | 20 | 15 |
| RUN 2 | 4320 | 225 | 1665 | 6 |
| RUN 3 | 1630 | 1630 | 8 | |
| TRI 1 | 1790 | 80 | 8 | |
| TRI 2 | 1380 | 590 | 790 | 13 |
| TRI 3 | 2710 | 850 | 6 | |
| TRI 4 | 1440 | 1440 | 8 | |
| TRI 5 | 1580 | 1580 | 9 | |
| TRI 6 | 1760 | 540 | 1220 | 12 |
| BAC 1 | 1460 | 1460 | 8 | |
| BAC 2 | 5100 | 3130 | 1970 | 33 |
| SEA 1 | 1430 | 1430 | 8 | |
| SEA 2 | 2260 | 660 | 1030 | 16 |
| Totals: | 34225 metres | 8385 metres | 13535 metres | 150 groynes |
| Note: Length of revetment includes both timber and block revetment structures. | ||||
Length of coastline under the N.N.D.C. jurisdiction for coastal
protection - 34 km
Highest cliffs - 75 metres
Dominant direction of littoral drift - South easterly
Highest astronomical tide - 2.7 metres above Ordnance Datum
Occurrence of highest astronomical tide - Late February, Early
November, Early December
Kelling Hard to West Runton - 6 to 8 metres
West Runton to Walcott - greater than 8 metres
Walcott to Cart Gap - 6 to 8 metres
Kelling Hard to West Runton - 0.3 to 0.4 metres
West Runton to Cart Gap - greater than 0.4 metres
Kelling Hard to West Runton - 0 to 500 kN/s
West Runton to Overstrand - 500 to 1000 kN/s
Overstrand to Trimingham - 1000 to 1500 kN/s
Trimingham to Bacton - 1500 to 2000 kN/s
Bacton to Walcott - 1000 to 1500 kN/s
Walcott to Cart Gap - 500 to 1000 kN/s
Kelling Hard to West Runton - 6000 to 9000 kN/s
West Runton to Trimingham - 9000 to 12000 kN/s
Trimingham to Walcott - greater than 12000 kN/s
Walcott to Cart Gap - 9000 to 12000 kN/s
1:100 year return period wave heights, mean wave height (1978-1986), mean annual along-shore wave energy and mean annual on/off-shore wave energy figures are taken from: The Sea Defence Management Study for the Anglian Region, Sir William Halcrow & Partners, 1988.