New York will use sidewalks to protect against urban flooding

A seven-mile-long sidewalk of innovative design will be built in the New York metropolitan area to protect the waterfront from storm surges. This interesting project on the prevention of urban flooding is part of the fashionable convention of sponge cities, an urbanistic concept to help adapt to climate change. What does it consist of?

New York City government’s million-dollar investment

July 15 this year. New York’s commissioner for Environmental Protection, Rohit T. Aggarawala, along with the commissioner in charge of design and construction, Tom Foley, announced at a press conference a new project to help prevent flooding in New York City. The installation of seven miles of special porous sidewalk along the waterfront in the Brooklyn borough will help stop some 132,000^{cubic meters of} stormwater precipitation per year, preventing it from entering the city’s sewer system.

During the conference, representatives of the administration demonstrated the effectiveness of the new sidewalk by pouring water on a previously prepared model. The sidewalk’s surface is extremely resilient – it can be driven on by a truck, while water quickly penetrates its porous structure. The sidewalk will be laid in the most flood-prone areas of Brooklyn. Work on the project is already underway and is expected to be completed in the fall of 2025. The entire investment will consume $32.6 million from the city’s budget.

Active prevention of urban flooding

As part of his justification for the costly project, Commissioner Aggarawala recalled Hurricane Ophelia, which hit New York in September 2023. At the time, the intensity of rainfall in Brooklyn reached as much as 7.5 cm per hour. Homes and service buildings were flooded, the functioning of public transportation was severely disrupted. The US insurance company Aon estimated that losses reached millions of dollars. After the storm, city authorities were accused of a number of oversights and negligence.

According to Aggarawala, climate change will promote an increase in the frequency and intensity of hurricanes, so it is necessary to implement solutions to protect New Yorkers from further disasters. On the other hand, torrential rains threaten as many as five metropolitan neighborhoods, where the sewer system is unable to absorb all the rainwater.

Porous sidewalks to protect against urban flooding are not, of course, the city government’s only idea. More widespread implementation of green infrastructure is planned to help the metropolis retain water without the risk of sewer overflows and storm overflows. In the future, there are plans to increase absorptive surfaces over a wider area of the city. This is a cheaper and more efficient solution than ditching streets and expanding underground infrastructure.

Unfortunately, installation of porous sidewalks is not possible everywhere. The decision to implement must be preceded by a study of the permeability of the soil below, and the installation itself involves the removal of the existing pavement at a depth of approx. 60 cm. Additional drainage elements are placed in the ground, which at the same time function as support for the porous concrete sidewalk slabs. Private underground infrastructure, as well as the existing sewer network, can be a hindrance to implementation.

Green infrastructure – the future for cities

The five boroughs of New York City have a total of 7,500. (more than 12 thousand km) of stormwater drainage networks and 150 thousand. storm overflows. This is the primary means of preventing urban flooding – unfortunately, insufficient under conditions of weather anomalies. That’s why, for more than a decade, the city government has been implementing the so-called Green Infrastructure Program to better protect residents and local businesses. The system is designed to capture rainwater before it even enters the sewer system, thus reducing the risk of flooding.

So far, the city has managed to implement 13,000 different retention and drainage installations, including more than 9,000 rain gardens along curbs. In addition to porous sidewalks, which allow rainwater to soak directly into the ground beneath the pavement, permeable paving stones are used, as well as green and blue roofs.

Blue roofs, popular in New York, allow rainwater to be collected in special tanks on the roofs of buildings and gradually released during dry periods. This idea is not only part of the prevention of urban flooding, but also helps reduce expenses for air conditioning (natural cooling of the building), and the water can be used, for example, for fountains. As an interesting aside, smart blue roofs are already being implemented in Ontario, Canada, from which rainwater is sent downhill to special reservoirs. After treatment, it can be reused, reducing water consumption by up to 56 percent.