Dune stabilisation
Dunes are a natural coastal feature on moderately exposed and exposed coasts. Dunes are formed by the sand, which blows inland from the beach and is deposited in the area behind the coastline.
Contents
Background
During storm surge events, the foot of the dunes can be eroded but the dunes act as a very flexible buffer zone, which protects the hinterland from erosion and flooding. The eroded material supplies material to the littoral budget minimising the general erosion along the entire section of shoreline. During the storm and also during more normal events, sand will be transported inland, sometimes in connection with the formation of wind alleys in the dune row. After the storm, the damaged dune will gradually be built up again, maybe slightly more inland. This means that a dune acts as a natural flexible coast protection and sea defence measures. It moves backwards parallel with the eroding coastline and at the same time it maintains its form and volume as well as a wide beach. This is a natural quasi-equilibrium situation. The erosion of dunes as a result of a severe storm surge is also referred to as dune erosion.
Dune vegetation
Barren dunes are susceptible to deflation by wind, with landward migration taking place. Vegetation plays an important role in stabilizing dunes. Different types of natural vegetation can settle on the beach and the front dune and are adapted to retain drifting sand. An overview of sand binding plants that are adapted to saline, nutrient-poor and harsh hydro-sedimentary conditions can be found in the article Shore protection vegetation.
However, the natural protection provided by beach and dune vegetation will be impaired if the plants are damaged by undergrazing, overgrazing or if beach-users, etc. generate too much traffic. Some uses such as golf courses typically fail to allow a sand dune system to move naturally. On the other hand, sand blowing inland can cause various kinds of damage to agriculture where adaptation to this natural movement of the dune does not occur. Consequently, authorities normally tend to protect dunes by regulating their use.
In some cases authorities have been eager to protect the dunes by planting marram grass and placing fences or fascines (placing of pine or spruce branches) in the wind alleys to trap the sand [1][2]. However, in some cases, this has resulted in complete fixing of the dune position and an unnatural growth in height. Consequently, the flexibility of the natural dune is lost resulting in a gradual disappearance of the dune due to erosion, whereby the protection, provided by the natural dune system, is lost.
Method
Planting marram grass and setting up spruce fascines for trapping of sand and enhancement of dune build up. Larger wind alleys can also be filled artificially prior to planting. However, as mentioned above, the protection should not be so comprehensive that it completely fixes the dunes.
Newly planted vegetation in particular can be strengthened by using fertiliser.
Restrictions for their use can also protect the dunes. Grazing in dune areas is prohibited in most countries, and authorities often limit public access. Such restrictions may regulate the traffic in the dunes, e.g. by prohibiting motor traffic. Different options are paved walking passages in areas near parking lots and fencing fragile newly planted areas.
Functional characteristic
Dune stabilisation by vegetation is a sustainable protection measure, enhancing the natural protection ability of dune areas. It provides some protection against wave and storm surge attack and at the same time it preserves the natural coastal landscape, if performed moderately. Dune stabilisation requires a planned and co-ordinated effort.
Applicability
Dune stabilisation is applicable on all coastal types where natural dunes occur. This is especially the case on moderately exposed to exposed coasts with perpendicular to very oblique wave (wind) attacks.
Artificial dunes are also used as a sea defence structure, see e.g. Climate adaptation policies for the coastal zone.
Related articles
References
- ↑ NSW 2001. Coastal Dune Management: A Manual of Coastal Dune Management and Rehabilitation Techniques. New South Wales, Department of Land and Water Conservation, Australia, http://www.environment.nsw.gov.au/resources/coasts/coastal-dune-mngt-manual.pdf
- ↑ USACE 2008. Coastal Engineering Manual. Part V, Ch. 7. Coastal Engineering for Environmental Enhancement pp. V.7.17-V.7.21. https://www.publications.usace.army.mil/USACE-Publications/Engineer-Manuals/u43544q/636F617374616C20656E67696E656572696E67206D616E75616C/
- ↑ Danish Coastal Authority, 1998. "Menneske, Hav, Kyst og Sand". (in Danish), (Man, Sea Coast and Sand in English). Kystinspektoratet 1973-1998.
Further reading
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.
Please note that others may also have edited the contents of this article.
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