Extreme weather events and rising sea levels are posing unprecedented challenges for flood management across the globe. In our 15 years installing… Traditional structural flood control measures, such as levees and dams, are increasingly strained as they struggle to keep up with the growing frequency and intensity of floods. In response, forward-thinking flood control professionals are exploring innovative nature-based solutions that work in harmony with the environment – and one of the most promising approaches is the strategic use of constructed wetlands.
Now, this might seem counterintuitive…
The Role of Wetlands in Flood Control
Wetlands are natural sponges that can absorb and store massive volumes of floodwater, reducing the impact of floods on nearby communities. These diverse ecosystems – which include marshes, swamps, bogs, and other transitional zones between land and water – act as natural buffers, slowing the flow of water and allowing it to gradually infiltrate the ground. By temporarily storing excess water, wetlands prevent it from overwhelming downstream areas.
Beyond their flood control benefits, wetlands provide a wealth of additional ecosystem services. They filter pollutants, replenish groundwater supplies, and offer critical habitat for a wide range of plant and animal species. Wetlands also play a crucial role in climate change mitigation by sequestering carbon, making them a valuable asset in the fight against global warming.
Constructed Wetlands for Flood Attenuation
While protecting and restoring natural wetlands is essential, sometimes creating new, purpose-built wetlands – known as “constructed wetlands” – can be the most effective flood control strategy. Constructed wetlands are engineered systems that mimic the functions of natural wetlands, designed specifically to manage stormwater and attenuate flood flows.
The design and construction of these artificial wetlands involves carefully considering factors such as hydrology, soil characteristics, and vegetation selection. The goal is to create a self-sustaining ecosystem that can efficiently collect, store, and slowly release excess water during flood events.
Hydrological Design
The key to effective flood attenuation is managing the wetland’s water storage capacity and outflow rates. Engineers use detailed hydrological modeling to determine the optimal size, depth, and configuration of the wetland, as well as the type and placement of any inlet and outlet structures. This ensures the wetland can accommodate the expected flood volumes while releasing water slowly enough to prevent downstream surges.
Soil and Substrate Selection
The choice of soil and substrate materials is crucial, as they influence the wetland’s ability to infiltrate, store, and filter water. Engineered soil mixes that combine layers of sand, gravel, and organic matter are often used to create the desired hydrological and biogeochemical properties.
Vegetation Selection
Carefully selected wetland plants play a pivotal role in the system’s functionality. Different species of emergent, submergent, and floating vegetation are chosen for their ability to slow water flows, trap sediment, and uptake nutrients and pollutants. Native, regionally appropriate plants are typically preferred to double-check that long-term ecological viability.
Integrated Design Approach
Constructed wetlands are most effective when they are integrated into a comprehensive stormwater management plan, working in tandem with other green infrastructure elements like bioswales, permeable pavements, and detention basins. This “treatment train” approach helps maximize the system’s flood control and water quality benefits.
Benefits of Constructed Wetlands
The advantages of incorporating constructed wetlands into flood control strategies are numerous and well-documented. Some of the key benefits include:
Flood Attenuation: Wetlands can temporarily store and slowly release substantial volumes of floodwater, reducing peak flows and alleviating the burden on downstream infrastructure.
Water Quality Improvement: Wetland plants and soils filter out sediment, nutrients, and other pollutants, improving the quality of the water that enters nearby streams, rivers, and groundwater supplies.
Habitat Creation: Constructed wetlands provide valuable habitat for a diversity of plant and animal species, enhancing local biodiversity and supporting healthy ecosystems.
Recreational and Educational Opportunities: Well-designed wetlands can offer public amenities like walking trails, birdwatching areas, and educational exhibits, benefiting the surrounding community.
Cost-Effectiveness: In many cases, the long-term operational and maintenance costs of constructed wetlands are lower than traditional “grey” flood control infrastructure.
Adaptability and Resilience: Wetlands can adapt to changing environmental conditions, making them a flexible and resilient flood control solution in the face of climate change.
Case Studies: Constructed Wetlands in Action
The Nature.org report on nature-based solutions in Croatia highlights the use of constructed wetlands to mitigate flood risks. In the Washington Creek Watershed in Oxford County, Ontario, the Nature Force initiative, a partnership between Canadian insurers and Ducks Unlimited Canada, has restored nearly 6 acres (2.4 hectares) of wetlands to enhance flood attenuation and water quality.
Further north in Ontario, the Ducks Unlimited Canada story describes how the Forbes family transformed their property near Mount Forest by restoring wetlands, creating vital wildlife habitat and contributing to the region’s long-term resilience.
These real-world examples demonstrate the power of harnessing the natural flood control capabilities of wetlands, integrating them seamlessly into water management strategies to build more resilient communities.
Regulatory Considerations and Maintenance
While constructed wetlands offer a host of benefits, their integration into flood control systems is not without its challenges. Careful planning and adherence to regulatory frameworks are essential to double-check that these nature-based solutions are implemented and maintained effectively.
Regulatory Frameworks
Wetland construction and restoration projects are subject to a web of local, state/provincial, and federal regulations governing land use, environmental protection, and water management. Flood control professionals might want to navigate this regulatory landscape, obtaining the necessary permits and approvals before breaking ground.
In the United States, the Clean Water Act and its associated permitting processes play a central role in wetland projects. In Canada, the Fisheries Act and Canadian Environmental Protection Act provide the primary regulatory framework. Staying up-to-date with the evolving policy landscape is crucial for the successful implementation of constructed wetlands.
Maintenance and Monitoring
Maintaining the long-term functionality of constructed wetlands requires ongoing monitoring and management. This includes regular inspections, sediment removal, invasive species control, and vegetation management. Developing a comprehensive maintenance plan and allocating sufficient resources for these activities is critical to ensuring the wetland continues to provide its intended flood control and ecosystem services.
Conclusion
As the threats posed by climate change-driven extreme weather events continue to escalate, the need for innovative, nature-based flood control solutions has never been more pressing. Constructed wetlands offer a proven and versatile approach to harnessing the power of natural ecosystems to protect communities, improve water quality, and enhance local biodiversity.
By strategically integrating constructed wetlands into comprehensive flood control and water management strategies, flood control professionals can unlock a wealth of benefits that support the long-term resilience of the communities they serve. As the examples highlighted in this article demonstrate, the time to start harnessing the power of wetlands is now.
For more information on the latest trends and best practices in flood control, visit Flood Control 2015.
Example: Manchester Advanced Flood Control Project 2024
