October 22, 2024
Sponge city concept helps manage stormwater runoff
BY NADINA GALLE
In recent years, city planners, landscape architects and green professionals have started to focus on designing urban spaces that work with nature instead of fighting against it.
A prime example of this approach is the "sponge city" concept, which was popularized by Chinese landscape architect Kongjian Yu, who won the 2023 Oberlander Prize for his innovative designs. This concept, rooted in ancient Chinese wisdom, aims to transform how cities handle floods by using "nature-based solutions." These solutions include: green spaces, green roofs, permeable pavements, constructed wetlands, rainwater harvesting and sustainable urban drainage systems like infiltration trenches, retention ponds and park-like reservoirs.
The sponge city design focuses on soaking up, storing and reusing rainwater, unlike traditional city planning, which relies on hard surfaces and sewer systems for flood control. This method reduces flooding and makes cities more resilient and sustainable.
Most sponge city practices originated in Asia, driven by the need to address violent monsoons, tropical storms and severe floods. However, the increasing frequency of extreme weather events worldwide highlights the need for sponge city principles everywhere. Additionally, many sponge city designs have not yet incorporated advanced technologies such as sensors, data analytics and algorithms that could enhance real-time flood management.
I discovered a notable example closer to home. This example not only embodies sponge city principles but also integrates technology to ensure adaptability in unpredictable conditions. In New York City, I met Adrian Benepe, who introduced me to the innovative Smart Water Garden Pond at the Brooklyn Botanic Garden.
Benepe has long championed urban green spaces. His career began as a Central Park ranger and he ultimately climbed the ranks to become New York City’s parks commissioner, where he led a major greening initiative in the early 2000s under Mayor Bloomberg. He then advanced the 10-Minute Walk Program at the Trust for Public Land, aiming to ensure all citizens have quality green spaces within walking distance.
Benepe embraced a new challenge in September 2020 as president and CEO of the Brooklyn Botanic Garden. Founded in 1910, this 52-acre garden next to Prospect Park features over 14,000 plants and attracts nearly one million visitors annually.
Benepe’s passion for the role extended beyond maintaining this urban oasis. He envisioned parks and gardens as blueprints for managing stormwater runoff through innovative water absorption techniques. With New York City facing stronger storms each year and resulting floods devastating neighbourhoods as recently as 2023, these techniques are more crucial than ever. Benepe was driven by the challenge of maintaining century-old botanical collections while transforming them into sponges that could help protect his neighbours’ homes.
Benepe’s awareness of the city's need for effective water absorption grew two months after he retired from the Parks Department, when Hurricane Sandy struck New York City. The storm caused up to $19 billion in damages, overwhelming the city’s centuriesold combined sewer system with five billion gallons of diluted sewage. This phenomenon, known as a combined sewer overflow (CSO), had severe consequences: buildings were destroyed, subway tracks and stations needed major redevelopment, basements experienced backups and dangerous bacteria levels in the water spiked.
This disaster made it clear to Benepe that Hurricane Sandy was only a preview of what climate change could bring. He felt compelled to find solutions to keep more water out of New York’s antiquated sewers during heavy rainfall, and his new position at the Brooklyn Botanic Garden provided the perfect opportunity.
On a wood-chipped path in the Japaneseinfluenced section of the garden, Benepe introduces me to his innovative solution. At first glance, it appears to be a picturesque wetland with a meandering path, a babbling brook and a tranquil pond surrounded by resilient plants thriving at the water’s edge.
He points out that this serene setting is, in fact, the Smart Water Garden Pond. Beneath the surface lies a sophisticated valve that continuously monitors weather conditions in real time. This system ensures that the water depth reaches two to three feet before triggering the valve to gradually release water throughout the garden. Anticipating significant rainfall, the valves release the necessary amount of water days in advance, maintaining steady water levels even during heavy storms.
This optimized process not only helps reduce Brooklyn's flooding by diverting 52 acres of discharge from the city's sewage system but also serves as a reservoir to sustain the garden’s thousands of plants during summer heat. They estimate the pond has reduced the garden’s outdoor freshwater consumption by nearly 96 per cent.
Benepe recalls how, in 2021, the pond faced its ultimate test. Heavy rain and the threat of flooding led many to believe that the pond should be drained in anticipation, given the strain already placed on New York’s sewage system. However, the weather-prediction algorithms advised against opening the valve. In the worst moments of the storm, Benepe admitted he questioned his decision to involve himself in the park’s drainage system.
A few days later, as the rain arrived, the pond came within inches of overflowing. But once the storm passed, the pond gradually drained its excess water over the following days. The surplus not absorbed by the garden was directed into a municipal sewage system that had not overflowed. The algorithm's decision proved to be the right one.
Like many cities, New York faces hefty fines from the U.S. Environmental Protection Agency for violating the Clean Water Act whenever CSOs occur. To mitigate costs and environmental impact, the city has long invested in green infrastructure to capture stormwater runoff before it enters the sewer system. While this approach began before Benepe’s tenure, it was significantly enhanced during his time when Mayor Bloomberg established a $1.6 billion fund to further intercept stormwater runoff, some of which was used to develop the Smart Water Garden Pond.
Benepe estimates that the pond keeps five million gallons of water out of the sewer each year. In terms of city-wide stormwater runoff, the pond is a drop in the bucket — just a few million gallons compared to the five billion the city reckoned with during Sandy. But on a hyper-local level, its effects are significant. Since its construction, nearby streets and homes have experienced reduced flood risks, providing residents with greater peace of mind.
Imagine if every street had a Smart Water Garden Pond, expertly managing water levels at precisely the right times. Such a transformation could turn the tide on flooding, offering a lifeline to communities, safeguarding properties and nurturing local ecosystems.
Dr. Nadina Galle spotlights Internet of Nature (IoN) technologies and practitioners making a difference in how we can optimize soil health, manage urban forests, create liveable cities, and everything in between. To learn more about the IoN and to catch episodes of the Internet of Nature Podcast, visit: nadinagalle.com.