The Lugeon Test: Methodology, Interpretation, and Applications in Geotechnical Engineering

Wetlands are highly effective natural systems that significantly reduce flood risks by acting as natural buffers and "nature's sponges". They play a crucial role in managing water flow and attenuating flood peaks, both for inland and coastal communities.

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Here's how wetlands contribute to flood risk reduction:

• Absorbing and Storing Water Wetlands absorb significant volumes of water during heavy rainfall and flood events, trapping and slowly releasing surface water, rain, and floodwaters over time. This reduces the speed and peak of flood waves. An acre of wetland, for example, can store up to 1.5 million gallons of floodwater. A hectare of wetland can store between 9,400 to 14,000 cubic meters of floodwater. Studies have shown that wetlands can capture up to 39% of floodwaters during storms.
• Reducing Peak Flows and Velocities By holding large volumes of water over wide areas, wetlands absorb rainwater runoff and prevent sudden, destructive floods. This effectively reduces the speed and peak of flood waves and desynchronizes flood peaks by holding back water, which reduces the volume and velocity of runoff reaching downstream areas simultaneously. Restoring or creating wetlands can significantly lower flood levels upstream by as much as two meters in some cases.
• Reducing Wave Energy and Coastal Surges In estuarine and coastal settings, wetlands contribute by absorbing the force of incoming water, thereby reducing wave energy and coastal surges.
• Enhancing Infiltration and Groundwater Recharge The dense vegetation and saturated soils promote infiltration into the ground, thereby recharging groundwater supplies. This increases the subsurface storage capacity of the landscape, reducing the volume of water that becomes surface runoff during subsequent rainfall events.
• Stabilizing Soil and Reducing Erosion The dense vegetation of wetlands also helps to reduce erosive forces and can contribute to maintaining channel capacity by reducing the amount of sediment washed into rivers.

Beyond flood control, wetlands provide a multitude of co-benefits, or ecosystem services:

• Water Quality Improvement They are natural water purifiers, filtering pollutants like heavy metals, sediment, nitrogen, and phosphorus.
• Biodiversity Enhancement Wetlands provide vital habitats for diverse wildlife species, including many threatened and endangered species.
• Carbon Sequestration Wetlands, especially peat wetlands, are significant carbon sinks, storing substantially more carbon than rainforests.
• Recreational and Educational Opportunities They offer spaces for activities like bird watching and can serve as educational areas.

Despite these benefits, approximately 90% of the world's wetlands have been lost since 1900, which has contributed to increased flood vulnerability. Restoring wetlands can significantly reduce the extent of flood damage by over 35%. Advancements in hydrodynamic and hydrologic modeling, such as the TELEMAC-2D model, are being used to quantify these flood mitigation benefits and produce high-resolution flood exposure maps for informed decision-making.