Introduction

Seawalls are large and engineered installations to protect the coast and shoreline from the impact of the sea. Most commonly, they are constructed as vertical armors along the coast. However, seawalls can also be built perpendicularly from the shore (in some contexts called “groins”) to manage the sediment budget of beaches. In addition, they can be freestanding in the sea at a distance from the shore (also called “breakwaters”). The structures can be combined with tetrapods and geotextile containers, among others. Due to their reverse risks, scale, and costs, seawalls should not be prioritized in the context of refugee settlements.

Benefits & Risks

Seawalls can benefit the shoreline protection and the uplands by mitigating the damaging effects of waves, tides or storm surges. However, the vertical design of seawalls results in the sharp reflection of the waves, which accumulate the energy at the bottom or toe of the structure which can lead to its deterioration over time. 

In general, the large coastal structures can cause extensive harm to the beaches as well as to the marine and coastal environment. In this light, larger coastal structures should be built only in combination with comprehensive environmental assessments and management.

Environmental Impact

Seawalls can harm the marine and coastal environment and biodiversity. In addition, they can cause interruptions in habitat migration.

Good Practice

Good Practice/Design Example: Tetrapod Concrete Block with Mangroves

The TetraPOT is a hybrid form of sea defense as it combines concrete blocks (also: tetrapod) and large pre-seeded and compostable plant pots for mangroves. Together with the mangrove root system, the blocks support flood defense, impede soil erosion, and protect natural habitats. The one-ton heavy tetrapod requires less concrete and production time than traditional sea defense bollards. In addition, the growing mangroves (protected from the concrete) can spread through holes in the engineered block. After around 14 months, the mangroves are grown enough to anchor the tetrapods through their roots (Tucker 2016).

References

Climate ADAPT    (2023):  Seawalls and jetties

Tucker, Emma    (2016):  TetraPOT is a greener alternative to concrete coastal defences , dezeen

Watson, Donald; Adams, Michele    (2010):  Design for Flooding: Architecture, Landscape, and Urban Design for Resilience to Climate Change , John Wiley & Sons Inc

Score Card

Criteria

Scale of Intervention

Shelter-Plot-Block Settlement Supra-settlement

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Type of Intervention

Engineered Nature-based Hybrid Non-structural

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Targeted Natural Hazard

Pluvial Flood Coastal/Riverine Flood

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Strategy Type

Relocate Reduce Hazard Magnitude Reduce Asset Vulnerability Reduce Casualties

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Implementation Time

Short (1 day ‐ 1 month) Medium (1 month ‐ 1 year) Long (> 1 year)

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Effect Duration

Short‐term ( <1 year ) Medium‐term (1 year to 10 years) Long‐term (>10 years)

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Targeted Vulnerable Assets

Buildings Transport Technical Infrastructure Land Cover

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Investment Costs

Low Medium High

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Maintenance Costs (yearly)

Low (<10% investment costs) Medium (10-50%) High (>50%)

Materials

Concrete, Metal, Timber, Steel (Selection)

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