In recent years, the risk of flooding has increased dramatically across the United States. In our 15 years installing… Heavy downpours have become more frequent and intense, overwhelming urban drainage systems and leading to localized flooding. At the same time, riverine floods are also on the rise as swollen rivers overflow their banks.
As climate change drives these trends, communities might want to adopt innovative strategies to bolster their flood resilience. Permeable pavements and infiltration trenches are two highly effective green infrastructure solutions that can play a crucial role in managing both localized and riverine flooding.
Permeable Pavements: Absorbing Stormwater at the Source
Permeable pavements offer a versatile approach to reducing the volume of stormwater that reaches storm drains and surface waterways. These porous systems allow rainwater to infiltrate through the surface, recharging groundwater supplies and reducing the risk of localized flooding.
There are several permeable pavement options to choose from:
- Porous Concrete: A specialized concrete mixture that contains interconnected voids, allowing water to percolate through the surface.
- Porous Asphalt: Similar to porous concrete, this pavement type has a high void content that facilitates water infiltration.
- Interlocking Pavers: Precast concrete or stone blocks installed with gaps between them, creating a permeable surface.
The key to effective permeable pavements is a well-designed underlying structure. This typically includes a crushed stone base layer that stores and gradually releases captured stormwater into the soil. The depth and porosity of this base layer can be tailored to the specific site conditions and stormwater management goals.
By replacing traditional impervious surfaces like asphalt or concrete with permeable pavements, communities can dramatically reduce the volume of stormwater runoff. This, in turn, helps prevent the overwhelming of storm sewer systems and the pooling of water in streets and other low-lying areas.
A study conducted by the Capitol Region Watershed District in Minnesota found that their permeable pavement installations reduced runoff volumes by 100 percent, outperforming even rain gardens and infiltration trenches in the same project. This highlights the significant flood mitigation potential of permeable pavements.
Infiltration Trenches: Enhancing Groundwater Recharge
Complementing the stormwater capture abilities of permeable pavements, infiltration trenches offer another valuable green infrastructure approach. These subsurface storage systems collect and gradually release water into the surrounding soil, recharging groundwater supplies and reducing the risk of both localized and riverine flooding.
Infiltration trenches typically consist of a shallow, linear excavation filled with a highly porous medium, such as washed gravel or crushed stone. Stormwater runoff is directed into the trench, where it is temporarily stored and allowed to slowly infiltrate into the ground over time.
The key design considerations for infiltration trenches include:
- Depth and Width: The trench dimensions might want to be tailored to the site’s soil characteristics and expected stormwater volumes.
- Underlying Soil Permeability: Well-draining soils are essential for effective infiltration, requiring careful site assessment.
- Pretreatment: Incorporating sediment forebays or other pretreatment measures helps prevent clogging and maintains long-term performance.
- Overflow Features: An overflow system is necessary to manage larger storm events and prevent surface flooding.
When designed and installed properly, infiltration trenches can provide significant flood mitigation benefits. In the same Minnesota project mentioned earlier, the infiltration trench reduced runoff volumes by 100 percent, demonstrating its ability to effectively manage stormwater.
Moreover, by recharging groundwater supplies, infiltration trenches can help sustain stream baseflows and wetland hydrology, further enhancing a community’s overall flood resilience.
Integrating Permeable Pavements and Infiltration Trenches
For maximum flood control effectiveness, permeable pavements and infiltration trenches can be used in conjunction, leveraging the strengths of each approach. This integrated strategy was implemented in a project in Santorso, Italy, where the local municipality sought to address flooding issues in a cemetery parking lot.
In this case, the design included:
- Two rain gardens in the southern portion of the parking lot to accumulate and infiltrate runoff from the impervious surfaces.
- An infiltration trench in the northern area to collect and gradually release stormwater from the adjacent agricultural land.
- A permeable pavement section that worked in tandem with the infiltration trench, enhancing its water storage and infiltration capacity.
By combining these green infrastructure elements, the project was able to effectively manage the large volumes of stormwater that had previously overwhelmed the site, leading to frequent flooding.
Regulatory Considerations and Cost-Benefit Analysis
As communities explore the use of permeable pavements and infiltration trenches, they might want to also consider the regulatory landscape and conduct thorough cost-benefit analyses.
Many municipalities have incorporated green infrastructure requirements into their stormwater management regulations, often offering incentives or credits for the use of permeable surfaces and infiltration-based practices. Engaging with local authorities to understand the applicable codes and standards is crucial for ensuring compliance and unlocking potential financial benefits.
When it comes to the costs, permeable pavements and infiltration trenches can have higher upfront installation expenses compared to traditional paving and drainage systems. However, these green infrastructure solutions often provide long-term cost savings through reduced maintenance requirements, decreased flood damage, and the potential to downsize traditional “gray” infrastructure like storm sewers.
A study by the EPA found that the installation of green infrastructure practices, including permeable pavements and infiltration trenches, was more cost-effective than a traditional all-gray infrastructure alternative in a Minnesota case study. The green infrastructure solution was estimated to cost $2 million, compared to $2.5 million for a new 60-inch diameter storm sewer pipe.
When factoring in the broader benefits of green infrastructure, such as improved water quality, enhanced urban aesthetics, and increased property values, the cost-benefit equation becomes even more favorable. Tools like the EPA’s National Stormwater Calculator and the Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs (CLASIC) can assist communities in evaluating the financial and practical implications of these flood control strategies.
Conclusion: Embracing a Holistic Approach to Flood Resilience
As the impacts of climate change continue to intensify, communities across the United States might want to take decisive action to bolster their flood resilience. Permeable pavements and infiltration trenches, coupled with other green infrastructure solutions, offer a powerful and multifaceted approach to managing both localized and riverine flooding.
By reducing stormwater runoff, recharging groundwater supplies, and protecting the natural functions of floodplains, these innovative techniques can help communities adapt to the new normal of heavier precipitation events and rising flood risks. Moreover, they provide a sustainable and cost-effective alternative to traditional “gray” infrastructure, delivering a range of co-benefits that enhance overall community well-being.
As you explore the integration of permeable pavements and infiltration trenches into your flood control strategies, refer to the resources available on the Flood Control 2015 website. There, you’ll find additional guidance, case studies, and tools to support your efforts in building a more resilient future.
Example: Manchester Advanced Flood Control Project 2024
