Shore protection, coast protection and sea defence methods
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This article aims to provide guidance for the development of shore protection, shore restoration and sea defence projects. See also the article: Protection against coastal erosion. In the first part some general principles are set forth. The second part is an introduction to technical shore protection methods, with links to more detailed articles.
- 1 General considerations
- 2 Practical guidelines for shore protection
- 3 Overview of types of coast protection, shore protection and sea defence
- 3.1 Coast protection
- 3.2 Mixed coast/shore protection by hard structures and beach fill
- 3.3 Shore Protection
- 4 References
- 5 Related articles
Shore protection is an important component of Integrated Coastal Zone Management (ICZM). Principles of ICZM are summarised in the recommendations of the European Union on Integrated Coastal Zone Management and also discussed in The Integrated approach to Coastal Zone Management (ICZM).
When focusing on shore protection, the following recommendations are relevant.
- A precondition for a successful shoreline restoration project is that all the parties involved have some understanding of coastal morphological processes; they are then in a position to understand why the present situation has developed and why certain solutions may work and others will not.
- Consider the coastal area as a dynamic natural landscape. Make only interventions in the coastal processes and in the coastal landscape if other interests of society are more important than preserving the natural coastal resource.
- Appoint special sections of the coast for natural development.
- Demolish inexpedient old protection schemes and re-establish the natural coastal landscape where possible.
- Minimise the use of hard coastal protection schemes, give high priority to the quality of the natural coastal resource.
- Preserve the natural variation in the coastal landscapes.
- Restrict new development/housing close to the coastline in the open uninhabited coastal landscape.
- Maintain and improve public access to and along the beach, legally as well as in practice.
- Reduce pollution and enhance sustainable utilisation of coastal waters.
Practical guidelines for shore protection
Below, the general recommendations are elaborated into practical guidelines for shore protection, shore restoration and sea defence projects.
- 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.
- 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 may be 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.
- Propose a funding distribution that reflects the fulfilment of the various goals, set by the parties involved.
- Allow protection measures only if valuable buildings/infrastructure are threatened.
- Choose a protection scheme that preserves sections of untouched dynamic landscape where possible.
- Use of a minimum number of hard structures required for achieving the protection objectives.
- Secure passage to and along the beach.
- Enhance the aesthetic appearance, e.g. by minimising the number of structures. Few and larger structures can be better than a lot of small structures.
- Preferably allow only projects which deal with an entire management unit/sediment cell and which secure maximum shore protection.
- Minimise maintenance requirements to a level that 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.
- Secure good local water quality and minimise the risk of trapping debris and seaweed.
- Secure safety for swimmers by avoiding structures generating dangerous rip currents. Avoid sheltered beaches (coves) as these give a false impression of safety for poor swimmers. Sheltered beaches may suffer from fine sediment trapping. If the water is too rough for swimming, a swimming pool, possibly in the form of a tidal pool, is a good solution.
- Provide good beach quality by securing that the beaches are exposed to waves, as wave action maintains attractive sandy beaches. This will of course limit the time that swimming is possible, but sheltered beaches often imply safety risks, poor beach quality and poor water quality.
- 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 achieved in many ways; protection of the coast and the hinterland against flooding often requires additional measures.
The choice of the measure in a given situation should consider three primary conditions:
- The problem (coast erosion, beach degradation or flooding)
- The morphological conditions (the type of coastal profile and the type of coastline)
- The land use (infrastructure/habitation, recreation, agriculture ,etc.)
Some measures have just a single function. This the case, for example, for a revetment, which provides local protection, but degrades the beach. Beach nourishment, on the other hand, protects against coastal erosion as well as against shore degradation. Different measures are detailed in the articles mentioned below. For a general understanding of coastal erosion, see the articles Natural causes of coastal erosion and Human causes of coastal erosion. Most of the content of the following sections is drawn from Mangor et al. 2017 .
Management of the coast
Fixing the coastline by structures
- Hard shoreline protection structures
- Hard structures and structural erosion
- Seawalls and revetments
- Emergency Protection
Mixed coast/shore protection by hard structures and beach fill
Mixed coastal protection and shore protection measures are schemes that combine hard structures and initial nourishment (called beach fill). These schemes can provide a solution that combines the ability of hard structures to directly protect a section of the coast and the ability of these 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. These schemes make use of littoral processes, either the longshore littoral drift and/or the cross-shore transport. Hard structures that may be used in these schemes are listed below, with links to a detailed article.
Groynes (see also Groynes as shore protection) are structures stretching out into the surf zone. They work by blocking (part of) the littoral drift, whereby they trap or maintain sand on their upstream side – at the expense of leeside shore erosion. 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 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 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 – see Modified breakwaters and headlands.
Ports or marinas
Ports or marinas may act as headlands at the same time as they serve their primary purpose of servicing vessels, see Accretion and erosion for different coastal types.
Perched beaches are natural or nourished beaches at locations with a steep shoreface. They are supported at their lower part by a submerged structure.
A cove is a sheltered sandy bay, formed by two curved shore-connected breakwaters at a coastline, which is otherwise protected by revetments.
Nourishment can be divided into three types:
- backshore nourishment,
- beach nourishment, and
- shoreface nourishment.
See the articles:
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 also apply for beach fill combined with structures.
- Mangor, K., Drønen, N. K., Kaergaard, K.H. and Kristensen, N.E. 2017. Shoreline management guidelines. DHI https://www.dhigroup.com/marine-water/ebook-shoreline-management-guidelines
- Protection against coastal erosion
- Types and background of coastal erosion
- Dune erosion
- Coastal Zone Management
- Structural erosion
- Coastal Hydrodynamics And Transport Processes
Please note that others may also have edited the contents of this article.
The part on the practical guidelines is written by Caitlin Pilkington
Please note that others may also have edited the contents of this article.