Artificial sand dunes

Dredging on Hammersee, Juist, Lower Saxony, Germany (2014)” showing earthworking machinery working in a coastal landscape, CC BY-SA 4.0 by Dietmar Rabich via Wikimedia commons.

Artificial sand dunes are a nature-based alternative solution to traditional ‘hard’ engineering approaches to coastal protection such as seawalls. Artificial dunes still rely on engineered structures, but mimic natural sand dunes, providing an ecologically beneficial barrier to protect coastal areas from erosion (Nordstrom, 2019). Artificial dunes are built using material which is dredged nearby or otherwise imported from offsite locations and held in place with engineered structures such as gabions, geotextile slopes, sand fences and clay cores. Planting is used to stabilise the dune surfaces (Makowski et al., 2013).

Artificial sand dune projects can occur in conjunction with ‘beach nourishment’, a technique that involves reshaping beach landscapes with machinery (Magliocca et al., 2011). They are distinct from of sand dune restoration or rehabilitation in that they take place in environments where there is no pre-existing dune, or a historic dune has been lost completely.

In the same way that hard engineering solutions to coastal erosion operate, artificial sand dunes are usually the first barrier between the sea and the land and provide crucial protection in storms from lower landward areas from storm surge and wave over wash (Makowski et al., 2013). By design, they become dynamic systems which adjust naturally to wind and wave action and changes in sea level and supplying or storing sediment in the beach environment as needed. They are most appropriate on wide, sandy beaches where their role protects the beach itself and allows dissipation of incoming wave energy.

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Name of NbS

Artificial sand dunes

Type of NbS

Hybrid living/engineered interventions

Location

  • Urban
  • Peri-urban
  • Rural

Case study:

Whangamatā dune restoration / construction

“Army Corps repairs and restores previously constructed coastal storm risk management project in Keansburg, NJ” showing earth working machinery and coastal engineered structures. Public domain.

Relationship to Indigenous knowledge

As a modern, engineered system, artificial sand dunes have a limited relationship to Indigenous knowledge in their design and implementation. They do, however, exist in sensitive coastal zones, that may have significance to local Indigenous people, represent food gathering places, or ancestral and spiritual landscapes especially in Te Moananui Oceania, where many Indigenous people relate to Ocean-going traditions (Anderson et al., 2006; Dickinson, 2014). There is precedence for Indigenous groups supporting engineered solutions that enhance the natural character and health, and preservation of these places (Waikato Regional Council, n.d.). See also a small scale sand erioisin protection method from Kiribati: Te buibui.

Climate change benefits
  • Coastal erosion / wave attenuation
  • Coastal inundation
  • Coastal salt-water intrusion into aquifers
  • Sea level rise 
  • Soil erosion
  • Storm surge

Artificial sand dunes mimic the qualities of natural dunes. See: dune preservation / restoration for details.

Artificial barriers, and hybrid solutions often installed immediately after major erosion events (storms) to prevent shoreline soil erosion can be modified over time by natural cycles. These can be implemented in a more intentional way as the first stage of artificial dune construction, and sometimes hard barriers will begin to accumulate sand forming as dunes over time naturally (Magliocca et al., 2011). Dune systems are important to the natural stability of coastal landscapes. Despite this, often engineered solutions ignore the significance of dune systems in sustaining coastal landscapes (Makowski et al., 2013).

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Societal / socio-cultural benefits
  • Climate change adapatation
  • Disaster risk reduction

By supporting natural processes of erosion, deposition, and retention of sediment in vegetation, the coastal landscape can shift and adapt to events as they occur in the same way that an unmodified dune landscape would (Nordstrom, 2019). Supporting this natural adaptability on the coastal edge and acting as a buffer zone, dunes clearly will reduce the risk of major impacts from natural disasters and protect landward areas and settlements including housing and infrastructure. Artificial sand dunes may require occasional repair or maintenance, but this is usually a straightforward process using sediment material on site (Linham & Nicholls, n.d.).

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Ecological and biodiversity benefits
  • Aesthetic value / artistic inspiration
  • Disturbance prevention (erosion, storm damage, flooding etc.)
  • Fresh water
  • Provision of raw materials
  • Recreation and tourism

The most obvious societal benefit of artificial sand dunes are the improved aesthetics provided by restored natural vegetation and landforms rather than hard structures (Nordstrom, 2019). This mimicking of natural infrastructure can improve nearby land values and visual appeal, attaining essential support from local people. Equally, the natural appearance of artificial dunes improves accessibility and recreational appeal of beach landscapes.

Artificial sand dunes can provide natural habitat, improving ecological and biodiversity outcomes in modified landscapes (Nordstrom, 2019). Naturally, coastal dunes contain highly variable flora and fauna (Makowski et al., 2013). Many coastal dune ecosystems have been degraded or destroyed, in part due to human impact, especially development in highly populated coastal areas.

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Technical requirements

Constructed sand dunes require careful consideration in their implementation (Nordstrom, 2019). One method involves the use of gabions, which are mesh baskets or structures filled with stone. Gabions can be constructed without heavy equipment enclosing many small components into a heavy mass to form core or retention structures. Additionally, attention must be paid to transport and equipment access, ensuring that the necessary machinery can reach the site. Mechanical burial is often necessary to establish these dunes effectively. Clay cores, commonly found in dams, present maintenance issues, while clay dykes, although extensive earthworks, and importing material like clay can be expensive. Hard components of artificial dunes like fencing and retention matting can create visual and access issues when exposed by erosion. Placement of artificial structures should be as close as possible to the infrastructure to be protected, allowing for natural functioning on the seaward side, promoting natural beach, and dune building processes. Rigorous monitoring is essential to ensure the effectiveness and longevity of constructed sand dunes (Nordstrom, 2019).

Issues and Barriers

An immediate barrier to aritificial sand dunes damage from natural sources including waves and currents, UV degradation of materials, and human impacts such as from access and vandalism. The impact of buried structures on the roots of dune vegetation and the water table are poorly understood.

Construction constraints mean artificial dunes are often much narrower than natural ones. Regulatory constraints can mean that the resulting dune structures must remain a certain shape and appearance, but the effect of small storms and non-storm erosion can expose structures at dune bases but leave unstable sand on top of the core structure (Nordstrom, 2019). The exposed hard cores can have different interactions with waves, potentially exacerbating erosion. Unstable sand and dangerous slopes produced by damaged artificial dunes can also cause difficulties for people accessing the beach. Beach cleaning or raking that subsequently takes place to (make beaches safe for recreation), is often unhelpful to natural process that artificial dunes aim to promote in a controlled way. (Provost et al., 2022)

If artificial dunes prevent delivery of sand upland to the beach, this can alter natural evolution of coastlines, that are generally naturally in a state of flux. This is an ongoing issue with engineered and hybrid coastal protection methods like artificial dunes, in that “at some point, storm damage can be expected to exceed design specifications of small projects … (and) without consideration of short-term advantages and long-term needs, designs cannot be considered resilient” (Nordstrom, 2019). Alteration of dune landscapes, although excluding most moderately damaging events and therefore protecting landward areas, structures and infrastructure, results in complex effects that extend beyond the timescale of singular events. The most significant effect humans interference has in these landscapes, including artificial dune construction and maintenance, is to rescale natural processes (Magliocca et al., 2011).

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Opportunities

Although dunes built with structural cores will include ‘hard’ engineered components, they can be considered ‘soft’ solutions and overcome regulatory restriction in this respect. This makes artificial dunes an opportune technique as frequency and severity of storms continues to increase and protection from inundation and flood risk becomes significantly important in developed and still developing coastal areas (Provost et al., 2022) of which Te Moananui Oceania has many (Kiddle et al., 2021). Another promising technique presented by Provost et al., (2022) is the placement of wrack (natural debris) at the dune toe in a manner that catches and consolidates sediment moved by wind and water at the edge of the dune face.

Financial case

Artificial dunes often occour at a reasonably small scale, being implemented by local councils or private organisations (Nordstrom, 2019). These can be a costly option, but can also be justified by revenue generated by tourism or high property values (Magliocca et al., 2011). All in all, the financial case is highly variable, and dependant on locale, scale and many other factors including ocean ecology and climate. Ongoing maintenance must be considered when hybrid engineered solutions are proposed to maintain positive effects and mitigate negative ones.

“Muriwai sand dune” showing eroded sand dune and forestry planting behind, CC BY 2.0 by Yortw via Flickr.
References
  • Anderson, A., Roberts, R., Dickinson, W., Clark, G., Burley, D., De Biran, A., Hope, G., & Nunn, P. (2006). Times of sand: Sedimentary history and archaeology at the Sigatoka Dunes, Fiji. Geoarchaeology, 21(2), 131–154. https://doi.org/10.1002/gea.20094
  • Dickinson, W. R. (2014). Beach ridges as favored locales for human settlement on Pacific islands. Geoarchaeology, 29(3), 249–267. https://doi.org/10.1002/gea.21476
  • Hesp, P. A. (2000). Coastal sand dunes: Form and function (CDVN Technical Bulletin No. 4). Forest Research.
  • Kiddle, G. L., Bakineti, T., Latai-Niusulu, A., Missack, W., Pedersen Zari, M., Kiddle, R., Chanse, V., Blaschke, P., & Loubser, D. (2021). Nature-Based Solutions for Urban Climate Change Adaptation and Wellbeing: Evidence and Opportunities From Kiribati, Samoa, and Vanuatu. Frontiers in Environmental Science, 9, 723166. https://doi.org/10.3389/fenvs.2021.723166
  • Linham, M. M., & Nicholls, R. J. (n.d.). Dune construction and stabilisation. UN Climate Technology Centre and Network. https://www.ctc-n.org/technology-library/protection-hard-engineering/dune-construction-and-stabilisation
  • Magliocca, N. R., McNamara, D. E., & Murray, A. B. (2011). Long-term, large-scale morphodynamic effects of artificial dune construction along a barrier island coastline. Journal of Coastal Research, 276, 918–930. https://doi.org/10.2112/JCOASTRES-D-10-00088.1
  • Makowski, C., Finkl, C. W., & Rusenko, K. (2013). Suitability of recycled glass cullet as artificial dune fill along coastal environments. Journal of Coastal Research, 289, 772–782. https://doi.org/10.2112/12A-00012.1
  • Nordstrom, K. F. (2019). Coastal dunes with resistant cores. Journal of Coastal Conservation, 23(1), 227–237. https://doi.org/10.1007/s11852-018-0653-6
  • Provost, L. A., Eisemann, E. R., Anderson, C. P., & Waldron, M. C. B. (2022). Wrack placement to augment constructed dunes: A field investigation. Frontiers in Built Environment, 8, 907608. https://doi.org/10.3389/fbuil.2022.907608Waikato Regional Council. (n.d.). Māori and the coast. Waikato Regional Council. https://www.waikatoregion.govt.nz/community/your-community/iwi/a-maori-perspective-te-ao-maori/maori-and-the-coast/