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.
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 . 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.
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.
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.
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. There is ample evidence for the effectiveness of sand fences to promote dune growth in periods of strong onshore winds, provided these are not accompanied by high water levels and waves. Several examples show that sand fences can also increase the stability of the dune belt during heavy storms.
- 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.
- Harris, M.E., Ellis, J.T. and Barrineau, P. 2020. Evaluating the geomorphic response from sand fences on dunes impacted by hurricanes. Ocean and Coastal Management 193: 105247
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.
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