Introduction

Next to engineered floodwalls (see Measure W.01 ), there are simpler dams, dikes, and levees made from local materials and without an impervious core. These can include piles of soil, earth, sand, wood, vegetation, stones, or rocks. Vernacular dams are a specific type of such nature-based dams. They describe structures created from locally available materials and use context-specific traditional knowledge and construction techniques.

Dikes and levees can also occur entirely based on geological processes. For example, naturally occurring dikes describe a body of rock blocking water flow, often originating from volcanic action. Natural levees form due to accumulated sediments (sand, gravels, silts, clay) after repeated flooding. Combining vernacular and natural dams with engineered structures (including an impervious core) can be particularly efficient regarding the environmental impact, risk protection, durability, and affordability of a dam, dike, or levee.

Benefits & Risks

Compared to engineered structures, vernacular dams, dikes, and levees benefit from their cost-effectiveness due to the local material use and simpler construction. In addition, they have a lower environmental impact than engineered dams because vernacular/natural dams usually seek to blend into the surrounding ecosystems and environmental context. Finally, vernacular structures are often based on local knowledge and community engagement.

However, vernacular dams, dikes, and levees are generally not as resistant to extreme weather events as engineered solutions and are more prone to erosion, overtopping, slope failure, and damage. That is also because they are commonly of smaller scale and do not involve the same safety features (e.g., flood gates) compared to engineered structures.

When constructing dikes, it should be considered that the constructions can lead to a more intense and faster river flow. Moreover, if dikes do not have a proper watertight core (as the engineered ones have) and are porous, the water may pass under the dike. Constructing vernacular dikes in regions with clay soils, wetlands, or marshes should also be avoided for the concern of environmental stressors and the risk of drying the areas up if they are not regularly flooded. Consequently, the vernacular dams themselves are often most effective in combination with engineered measures.

Environmental Impact

Due to their natural occurrence or the use of locally available materials, the environmental impact is comparatively low, and vernacular solutions tend to blend into the surrounding ecosystems. However, dikes and levees can lead to a more intense and faster river flow, erosion, or slope failure. In regions with clay soils, wetlands, or marshes, their construction could trigger environmental stressors and the drying up of the surrounding areas.

Good Practice

Lessons Learned: Earthen Dike in the Al-Redis Refugee Camp, Sudan

To protect the residential areas in the Al-Redis refugee settlement in Sudan, an earthen dyke alongside the settlement was constructed during an emergency in 2022. Although the dike has a protective impact on the shelters, it cannot ensure appropriate access during long time periods of the year. That is due to the inundation of the access road to the settlement which could not be averted by the dike.

References

AEC Geosynthetics    (2020):  Riverbank and Channel Protection - Levees and Dikes

Martinez, Maria; Bakheet, Ramez; Akib, Shatirah    (2021):  Innovative Techniques in the Context of Actions for Flood Risk Management: A Review , Eng

Tariq, Muhammad Atiq Ur Rehman; Farooq, Rashid; van de Giesen, Nick    (2020):  A Critical Review of Flood Risk Management and the Selection of Suitable Measures , Applied Sciences

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

Soil, Sand, Wood, Vegetation, Stones, Rocks; Coir (Husk of coconut shell)

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