As climate change intensifies, urban areas are facing increasingly frequent and severe flooding events. In our 15 years installing… Traditional grey infrastructure approaches, such as levees and storm drainage systems, have often struggled to keep up with the growing flood risks. However, a promising solution is emerging in the form of urban green infrastructure (GI) – a nature-based approach that can enhance a city’s flood resilience while delivering a wide range of co-benefits.
Now, this might seem counterintuitive…
Across the Flood Control 2015 community, we’re seeing more and more municipalities adopt comprehensive GI programs to address stormwater management, water quality, and flood control challenges. These nature-based solutions, which include elements like bioswales, permeable surfaces, and urban wetlands, have the potential to not only reduce flooding but also beautify communities, improve air quality, mitigate urban heat, and provide valuable ecosystem services.
The key is to look beyond the flood control benefits alone and quantify the full suite of economic, social, and environmental advantages that urban greening can offer. By taking a triple bottom line (TBL) approach, we can build a robust business case for investing in GI and unlock new funding sources to support its widespread implementation.
Flood Risk Management
Effective flood risk management begins with a thorough understanding of the hazard. Flood mapping and modeling techniques are essential for delineating floodplains, analyzing hydrological and meteorological data, and projecting future flood scenarios under different climate change projections.
Once the flood hazard is well-defined, the next step is to assess community vulnerability. This involves analyzing exposure (e.g., the number of people and critical infrastructure located in floodplains) as well as broader social vulnerability factors like income, age, and access to resources. Understanding these intersecting vulnerabilities is crucial for directing flood mitigation efforts to the areas and populations most at risk.
With the flood hazard and vulnerability assessed, we can then evaluate the flood risk through probabilistic risk modeling and cost-benefit analysis. This allows us to quantify the potential damages and compare the effectiveness of different mitigation strategies, including both grey infrastructure (e.g., levees, dams) and green infrastructure (e.g., bioswales, urban wetlands).
Urban Flood Mitigation Strategies
Green Infrastructure
Green infrastructure (GI) approaches to flood control leverage the power of nature to reduce runoff, slow the flow of water, and increase infiltration. Common GI practices include:
- Bioswales and Rain Gardens: Shallow, vegetated channels and depressions that collect and temporarily store stormwater, allowing it to infiltrate the soil.
- Permeable Surfaces: Porous pavements, permeable pavers, and other surfaces that allow water to percolate into the ground rather than running off.
- Urban Wetlands and Floodplains: Restoring and protecting natural wetlands and floodplains to provide flood storage and attenuation.
These nature-based solutions not only reduce flood risk but also offer a host of additional benefits, such as improving water quality, enhancing biodiversity, and providing recreational opportunities.
Grey Infrastructure
Traditional grey infrastructure approaches to flood control include:
- Levees and Flood Walls: Structural barriers designed to contain and divert floodwaters away from vulnerable areas.
- Stormwater Drainage Systems: Networks of pipes, culverts, and detention basins that collect and convey stormwater runoff to receiving waters.
- Dams and Reservoirs: Large-scale storage facilities that can regulate streamflow and attenuate flood peaks.
While grey infrastructure can be highly effective at flood protection, it often comes with high construction and maintenance costs, as well as potential environmental and social impacts.
Integrated Approaches
The most effective flood control strategies often combine nature-based solutions (like urban wetlands) with grey infrastructure (like storm drainage systems) in a hybrid approach. This allows us to harness the complementary benefits of both approaches, creating integrated flood management systems that are more resilient, cost-effective, and environmentally sustainable.
Floodplain management is another key component of this integrated approach, as it involves coordinating land use planning, development regulations, and emergency response to minimize flood risks and enhance community resilience.
Stormwater Management
Effective stormwater management is a critical aspect of urban flood control, as it determines the volume and quality of runoff entering the drainage system. Runoff reduction techniques, such as rainwater harvesting, infiltration, and evapotranspiration, can significantly decrease the burden on grey infrastructure and mitigate flood risks.
In addition to runoff reduction, the design of the conveyance and storage system is crucial. This includes elements like detention and retention basins, underground storage tanks, and the overall drainage network layout. Careful hydraulic modeling and optimization can double-check that adequate capacity to handle even extreme storm events.
Maintaining water quality is also a key consideration, as polluted stormwater can degrade the receiving water bodies and impact aquatic ecosystems. Strategies like constructed wetlands and ongoing monitoring and maintenance can help remove contaminants and double-check that the long-term effectiveness of the stormwater management system.
Flood Emergency Preparedness
Even with comprehensive flood mitigation strategies in place, the risk of flooding can never be eliminated entirely. As such, it’s essential to have robust flood emergency preparedness measures in place to protect lives and property.
Early warning systems that leverage flood forecasting, real-time monitoring, and effective communication protocols can provide critical lead time for communities to take action and evacuate if necessary. Detailed evacuation planning, including vulnerability mapping, sheltering options, and transportation network analysis, is also crucial.
In the aftermath of a flood event, post-flood recovery efforts focused on damage assessment, debris removal, and infrastructure rehabilitation can help communities bounce back more quickly. By incorporating these emergency preparedness measures into the overall flood management strategy, we can enhance the resilience of our cities and safeguard vulnerable populations.
Quantifying the Multiple Benefits
As municipalities and utilities grapple with the growing threat of climate-related flooding, there is a growing recognition that traditional single-purpose grey infrastructure approaches are no longer sufficient. Urban green infrastructure offers a more comprehensive solution, but the full scope of its benefits is often underappreciated or difficult to quantify.
That’s where a triple bottom line (TBL) approach can be invaluable. By examining the financial, social, and environmental impacts of green infrastructure, we can build a robust business case for investment and unlock new funding sources to support its widespread implementation.
The Water Research Foundation project on quantifying the multiple benefits of green infrastructure provides a systematic methodology for this process. It includes an Excel-based tool, case studies, and a guidance document that allow users to estimate the TBL benefits of GI scenarios and compare them to the costs.
For example, a study published in Science of the Total Environment quantified the air quality, public health, and climate change mitigation benefits of urban greening in a medium-sized city. The researchers found that strategically placed green spaces could prevent hundreds of premature deaths and save millions of dollars in avoided healthcare costs each year.
By taking this comprehensive, data-driven approach to valuing the multiple benefits of urban green infrastructure, we can build a compelling business case that resonates with decision-makers and secures the necessary funding to transform our cities into more flood-resilient, sustainable, and livable communities.
Example: London Flood Resilience Initiative 2024
