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N.18 Sand Dune Management and Restoration
Introduction
Dunes are natural flood barriers that protect the inland from the brunt of coastal floods and storm surges. The sandy ridges develop in parallel to the shoreline. Dunes change their size and shape due to tides, winds, storms, or heavy sea. In case of flooding, the health of the vegetation can decide upon the effectiveness of the dune’s mitigation capacity.
The restoration of dunes includes the recovery of eroded areas and dune stabilization based on vegetation (e.g. dune-forming perennial grasses) and fences. In general, the interventions that join the restorations of dunes should not disrupt the natural forming processes and the dune ecosystems. A careful assessment of the site before the implementation of measures is highly recommended.
Benefits & Risks
Compared to engineered dams, dune systems depend on more space between the shore and the developed inland to reach the highest efficiency. A sand dune with a narrow beach close to a developed area has a smaller flood mitigation impact than one with a wide and large beach. Overall, coastal development and increasing urbanization describe a severe threat for the health and effectiveness of dune systems.
Environmental Impact
Sand dune restoration supports the protection of ecosystems and biodiversity. In addition, healthy sand dunes help mitigate coastal erosion and storm surges.
Good Practice
Sand Dune Restoration in S. João da Caparica, Portugal
The Portuguese city of Almada lies at Atlantic coast. It faces sea-level rise, increasing erosion, the threat of storm surges, and extreme flooding. As a result, the project ReDuna was initiated in 2014 to prioritize dune restoration, coastal protection, biodiversity targets, and community awareness in the urban area of Almada.
After the destruction of the dune ecosystem due to winter storms, the project began with the dune restoration by installing willow, fences, pathways, and around 100’000 native plants along 1 km of the shore. After installing these measures within 6 months, a monitoring system continuously assessed the sand dune ecosystem. The Faculty of Science of Lisbon University, Center of Ecology led the monitoring which included, among other analyses, the site’s geomorphological changes via GPS. After four years of monitoring, the results showed increased biodiversity, more stability in sediment transfer, and that the planted vegetation had formed a dense and effective root system (as deep as four meters) for dune stabilization. The Storm Emma in 2018 proved the regained efficiency of the sand dunes.
In addition, the local community was involved in the design process and maintenance campaigns. The actions for maintenance (including the removal of alien species) take place after each summer and storm season. The EU Structural and Cohesion Fund financed the structural interventions at the beginning of the project. The municipality then paid for the monitoring and human resources (Connecting Nature 2020).
References
Climate ADAPT (2023): Dune construction and strengthening
Connecting Nature (2020): ReDuna - Restoration of S. João da Caparica Sand Dunes
Naturally Resilient Communitites (n.d.): Using Nature to Adress Flooding
UKCEH; UK Sand Dune and Shingle Network and Dynamic Dunescapes partners (2021): The Sand Dune Managers Handbook - 1st ed.: Produced for the Dynamic Dunescapes (DuneLIFE) project: LIFE17 NAT/UK/000570; HG-16-08643
Score Card
Environmental Impact
Risk Protection
Affordability
Durability
Criteria
Scale of Intervention
Shelter-Plot-Block Settlement Supra-settlement
Type of Intervention
Engineered Nature-based Hybrid Non-structural
Targeted Natural Hazard
Pluvial Flood Coastal/Riverine Flood
Strategy Type
Relocate Reduce Hazard Magnitude Reduce Asset Vulnerability Reduce Casualties
Implementation Time
Short (1 day ‐ 1 month) Medium (1 month ‐ 1 year) Long (> 1 year)
Effect Duration
Short‐term ( <1 year ) Medium‐term (1 year to 10 years) Long‐term (>10 years)
Targeted Vulnerable Assets
Buildings Transport Technical Infrastructure Land Cover
Investment Costs
Low Medium High
Maintenance Costs (yearly)
Low (<10% investment costs) Medium (10-50%) High (>50%)
Materials
Native Vegetation (For example, dune-forming perennial grasses such as sand couch, sea Lyme or marram grass), fences, (wooden) posts, wood for boardwalks