How green stormwater infrastructure can help cities manage intense rainfall events

Effects of cloudbursts

Extreme rainfall events are also called cloudbursts. They are short, intense storms that are becoming more frequent due to climate change. Cloudbursts pose challenges for community planners and managers. These extreme rainfall events can overwhelm existing drainage systems. They cause flash flooding, damage critical infrastructure, and pollute our waterways and ecosystems.

Cloudbursts also affect the social and economic well-being of residents. That is especially true for those who are more vulnerable to the impacts of flooding.

Adaption and mitigation strategies

With cloudbursts happening more often, cities are turning to innovative and resilient approaches. Instead of relying only on underground pipes and reservoirs, they are focusing on solutions that use natural elements. These elements use vegetation and soil to control stormwater on the surface.

A few examples include:

• Creating cloudburst boulevards. These divert excess water to nearby parks or water bodies.
• Building green stormwater infrastructure in combination with traditional piped infrastructure. The goal is to cleanse stormwater runoff.
• Transforming underutilized lots and parks into multifunctional spaces that can collect and store rainwater.

It’s rewarding to help communities prepare for cloudburst events and hear that our designs are working. Here are techniques our team has used in our work with communities across North America.

Blue-green corridors

Blue-green corridors offer resilient infrastructure that connects natural habitats and urban settings. The corridors combine networks of linear water features with green spaces. They use natural systems to manage water and reduce flooding.

This solution also helps cities restore and manage natural ecosystems like wetlands, forests, grasslands, or urban green spaces to protect against cloudbursts. The benefits are huge. These ecosystems can reduce runoff, increase infiltration, buffer floods, improve water quality, and enhance biodiversity.

In New Orleans, Louisiana, we are leading the design of the Blue-Green Corridors project in the Gentilly Resilience District. These corridors convey and store excess stormwater, which enhances the capacity of the drainage network. This project aims to reduce flood risk, slow land subsidence, and revitalize neighborhoods. The district will create a network of canals, parks, and community spaces along three miles of public right-of-way and six public parcels.

Along the streets slated as “blue corridors,” the City will construct open channel canals within the wide, neutral grounds between vehicle travel lanes to receive and manage runoff. During storms, this will quickly relieve stress on the pumping system, allowing it to catch up.

On streets identified as “green corridors,” rain gardens will store stormwater runoff and let it seep slowly back into the ground. Wherever possible, the project will also reconfigure roads. That will help reduce impervious cover, beautify the neighborhood with landscaping, calm traffic, and build complete streets for safe walking and biking.

Master planning and gray-green stormwater infrastructure

Another effective plan to help manage stormwater runoff during cloudburst events is building out gray-green stormwater infrastructure.

Gray infrastructure is the traditional way to manage rainfall. It is designed to move stormwater away from the built environment and impervious surfaces—roadways, parking lots, and rooftops—into collection systems such as gutters, curbs, and drains.

Alongside that, green infrastructure is designed to mimic nature and capture rainwater where it falls. The goal? Reduce and treat stormwater at its source as much as possible. Green infrastructure can reduce the volume and peak flow of stormwater entering the gray infrastructure system. It also adds value to the community. It improves aesthetics, encourages socialization, increases property values, and decreases the economic and impacts of flooding. 

In Chicago, Illinois, we created a stormwater master plan (SMP) utilizing a gray-green approach for the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC). We focused on three underinvested communities on the west side of the city. The projects would address hyperlocal neighborhood drainage issues and increase tree canopy. They also reduce urban heat island effects.

We wanted to focus on projects that could be coupled with conveyance improvements. To do this, we scored potential green stormwater infrastructure projects in several categories. They included volume captured, efficiency of the design, and expected cost. Projects that were on streets with pipe upgrades and had a large available footprint and sufficient loading ratios or lower costs got higher rankings.

In our analysis, we identified more than 60,000 feet of pipe upgrades and 125 green stormwater systems to be bundled into recommended project packages in the SMP. The MWRDGC or its partner agencies can implement each bundled project as a stand-alone one. Or each project can be an add-on to other City infrastructure projects.

Community revitalization

Flooding leaves a mark on the social and emotional well-being of communities. It can affect the sense of belonging and social cohesion. It can also disrupt their normal routines when it comes to access to education, health care, transportation, communication, or recreation. This reduces quality of life and the occasions for social interaction and participation.

Here are some ways green stormwater can improve the social well-being of communities.

• It improves physical and mental health. Thoughtful projects provide space for recreation and physical activity. They encourage walking, biking, or playing in parks and green spaces.
• It strengthens social cohesion and safety. Green stormwater infrastructure creates places for social interaction and participation.  That fosters a sense of community and belonging among residents. In turn, this can boost social capital, trust, cooperation, and civic engagement.
• It enhances economic development and equity. Improving access to green spaces among different groups of people promotes environmental justice and equity. This could help address the inequalities in urban areas that often affect low-income and minority populations.

In Ottawa’s Sandy Hill Community Park we’ve successfully integrated a major flood-control facility with an existing community center and residential park. It has helped revitalize the urban neighborhood. Our team showed that a stacked storage solution in a low-lying park of Sandy Hill was the best option. Then we tapped into our water engineering and landscape architecture practices and launched a robust community relations campaign.

The Sandy Hill facility is a tiered flood-management system. Though the public can’t see it, the convertible multisport field integrates green and traditional gray infrastructure. Under normal weather, a surface detention area remains dry for public use and lies over an underground tank. When heavy rainfall inundates the nearby roads, the system directs flooding into the park and away from backing up into the basements of area homes.

Sandy Hill Community Park serves as a hub for residents to enjoy recreational activities and social events. It features a community center, sports field, winter ice skating rink, wading pool, children’s play area, and casual open spaces. The award-winning park is now an established destination for gatherings.

Bettering communities with green stormwater infrastructure

Cloudbursts are more common. And communities are investing in resilient infrastructure to cope with them. How? They’re using innovative stormwater management corridors, green-gray solutions, and dual-use community spaces. It’s exciting to help people improve their neighborhoods, and we’re looking forward to working with more communities on sustainable solutions.

Cities can build resilience to extreme weather events in a sustainable, inclusive way. They just need to be more thoughtful about design and funding while balancing community needs and desires.