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Shore protection, coast protection and sea defence methods

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General Considerations

A precondition for a successful shoreline restoration project is that all the parties involved have some understanding of the coastal morphological processes. They are then in a position to understand why the present situation has developed and why certain solutions will work and others will not.

The following should be considered in connection with shoreline protection and management projects:

  1. Consider the coastal area as a dynamic natural landscape. Make only interventions in the coastal processes and in the coastal landscape if the interests of the society are more important than preserving the natural coastal resource.
  2. Appoint special sections of the coast for natural development.
  3. Demolish inexpedient old protection schemes and re-establish the natural coastal landscape where possible.
  4. Minimise the use of coastal protection schemes, give high priority to the quality of the coast resource, and concentrate on shore protection.
  5. Preserve the natural variation in the coastal landscapes.
  6. Restrict new development/housing close to the coastline in the open uninhabited coastal landscape. Allow only such facilities, which require access to the sea.
  7. Maintain and improve the public access to and along the beach, legally as well as in practice.
  8. Reduce pollution and enhance sustainable utilisation of coastal waters.

This leads to the practical guidelines for shore protection in connection with coast protection, shore protection and shore restoration projects. They are mentioned in the next paragraph.

Practical guidelines for Shore Protection

  1. Work with nature, for instance by re-establishing a starved coastal profile by nourishment and by utilising site-specific features, such as strengthening semi-hard promontories.
  2. Select a solution which fits the type of coastline and which fulfils as many of the goals set by the stakeholders and the authorities as possible. It is quite often impossible to fulfil all goals, as they are often conflicting and because of budget limitations. It should be made clear to all parties, which goals are fulfilled and which are not. The consultant must make it completely clear what the client can expect from the selected solution; this is especially important if the project has been adjusted to fit the available funds.
  3. Propose a funding distribution, which reflects the fulfilment of the various goals, set by the parties involved.
  4. Manipulate the rate and gradient of the littoral drift rate and gradient by use of a minimum number of structures. Preserve sections of untouched dynamic landscape where possible. Allow protection measures only if valuable buildings/infrastructure are threatened. This policy will preserve the natural coastal resources and the neighbouring sections will receive material as a result of erosion in the unprotected area.
  5. Secure passage to and along the beach.
  6. Enhance the aesthetic appearance, e.g. by minimising the number of structures. Few and larger structures is normally better than a lot of small structures. Preferably allow only projects which deal with an entire management unit/sediment cell and which have maximum shore protection. Individual projects tend to concentrate on coast protection.
  7. Minimise maintenance requirements to a level, which the owner(s) of the scheme is able to manage. A stand-alone nourishment solution may at first glance appear ideal, but it will normally not be ideal for the landowners, as recharge will be required at short intervals.
  8. Secure good local water quality and minimise the risk of trapping debris and seaweed.
  9. Secure safety for swimmers by avoiding structures generating dangerous rip currents. Avoid protected beaches as these give a false impression of safety for poor swimmers. Protected beaches at exposed sites tend to suffer from sand trapping in the sheltered area. If the water is too rough for swimming, a swimming pool, possibly in the form of a tidal pool, is a good solution.
  10. Provide good beach quality by securing that the beaches are exposed to waves, as the waves maintain the attractive sandy beaches. This will of course limit the time when swimming is possible, but making protected beaches often means safety hazards, poor beach quality and poor water quality.
  11. Be realistic and pragmatic, keeping in mind that the natural untouched coastline is utopia in highly developed areas. Create small attractive locations at otherwise strongly protected stretches if this is the only realistic possibility.


Overview of Types of Coast Protection, Shore Protection and Sea Defence

Protection of the coast and the shore against the erosive forces of waves, currents and storm surge can be performed in many ways, and protection of the coast and the hinterland against flooding adds even more types to the protection defence measures.

The choice of the measure in a given situation depends on the three primary conditions:

  1. The problem (coast erosion, beach degradation or flooding)
  2. The morphological conditions (the type of coastal profile and the type of coastline)
  3. The land use (infrastructure/habitation, recreation, agriculture etc.)

Some of the measures have mainly one function, which e.g. is the case for a revetment. It protects the coast against erosion, but aggravates shore erosion. Beach nourishment, on the other hand, protects against coast erosion as well as against shore degradation.

Coast Protection

Management of the coast

Dune stabilisation

Cliff stabilisation

Fixing the coastline by structures

Seawall

Revetment

Emergency Protection

Bulkhead

Mixed Coast/Shore Protection by Structures and Beach Fill

Mixed coastal protection and shore protection measures are schemes, which combine structures and initial nourishment, which is called beach fill. These schemes are an attempt to find a solution, which combines the ability of the structures to directly protect a section of the coast with the ability of the structures to support and maintain beach filling/nourishment. The result is protection of the beach and protection of the coast behind the beach. The advantage of this combination is that it minimises the requirements for regular recharging of the fill, or nourishment. The relevant structures in connection with this have characteristics, which make use of the littoral processes, either the longshore littoral drift and/or the cross-shore transport. The relevant structures are listed below with links to a detailed article.

Groynes

Groynes (see also groynes as shore protection) are straight structures perpendicular to the shoreline. They work by blocking (part of) the littoral drift, whereby they trap or maintain sand on their upstream side. Groynes can have special shapes; they can be emerged, sloping or submerged, and they can be single or in groups, the so-called groyne fields.

Detached breakwaters

Detached breakwaters are straight shore-parallel structures, which partly provide shelter in their lee thus protecting the coast and decreasing the littoral transport between the structure and the shoreline. This decrease of transport results in trapping of sand in the lee zone and some distance upstream. Breakwaters can also deviate from the straight and shore-parallel layout, they can be emerged and submerged, and they can be single or in groups, the so-called segmented breakwaters.

Headlands

Headlands are smooth structures built from the coastline over the beach and some distance out on the shoreface. They work by blocking (part of) the littoral transport. A headland combines the effects of groynes and detached breakwaters and at the same time, minimises some of the disadvantages of groynes and breakwaters.

Ports or marinas

Ports or marinas may act as headlands at the same time as they serve their primary purpose of servicing vessels.

Perched beaches

Perched beaches are natural or nourished beaches at locations with a steep shoreface. They are supported at their lower part by a submerged structure.

Coves

A cove is a semi-protected sandy bay, formed by two curved shore-connected breakwaters at a coastline, which is otherwise protected by revetments.

Shore Protection

Nourishment

Nourishment can be divided into three types:

  • backshore nourishment,
  • beach nourishment, and
  • shoreface nourishment.

Nourishment as part of a shoreline management project, which combines structures and initial nourishment - also referred to as Beach Fill - will not be discussed here; however, the general considerations regarding nourishment, as discussed in the article shore nourishment, also apply for beach fill combined with structures.

References

  • Mangor, Karsten. 2004. “Shoreline Management Guidelines”. DHI Water and Environment, 294pg.

See also


The main author of this article is Mangor, Karsten
Please note that others may also have edited the contents of this article.


The part on the practical guidelines is written by Pilkington, Caitlin

The main author of this article is Pilkington, Caitlin
Please note that others may also have edited the contents of this article.