May 21, 2024

New Hydraulic Model Will Allow DEP to Implement Efficient Solutions to Maximize Existing Sewer Capacity and Divert Stormwater Flow Away from Overwhelmed Neighborhoods

The New York City Department of Environmental Protection (DEP) today announced that it has developed a citywide hydraulic model of the 7,500 miles of sewers that serve all five boroughs. This innovative technology allows DEP’s engineers and planners to simulate how the City’s network of pipes performs under a range of storm scenarios. This data-driven approach, coupled with the City’s rainfall-based flooding maps, will allow the agency to focus on communities most susceptible to flooding, test various solutions, and make cost-effective investments that will bring cheaper and faster relief to residents.

“DEP has achieved a major milestone by completing this citywide hydraulic model of our sewer system. This digital tool builds on our commitment in PlaNYC to seek solutions to the flooding caused by climate change-induced storms,” said DEP Commissioner Rohit T. Aggarwala. “The data gathered from this in-depth analysis will guide our future stormwater management decision-making and help us assess the infrastructure needs of New York City’s most flood-prone locations.”

In 2020, the US National Climate Assessment reclassified New York City from the coastal temperate climate zone to the humid subtropical climate zone—a recognition that we now live in a place that our infrastructure was not designed for. Heavy storms that were once exceptional have become commonplace. With sudden, powerful storms bringing more intense rainfall to New York City, DEP is adapting its stormwater management strategies accordingly. This hydraulic model, combined with flood maps and 311 complaint data, will give DEP engineers and planners a more thorough understanding of the true scale of the flooding issues caused by climate change and the strain it puts on certain parts of the sewer system.

When planning for a project, DEP’s analysis focuses on the critical components of the sewer system, including the trunk mains. These large arterial pipes serve as the backbone of the system and are responsible for moving substantial amounts of stormwater. By using a hydraulic model of the City’s entire sewer network, DEP can maximize the potential of the existing system. For example, DEP can identify trunk mains with unused capacity in a storm scenario and, with relatively small capital construction investments, modify the network to shift stormwater flows from pipes that are overwhelmed and causing flooding to those with available space.

A case study where hydraulic modeling was successfully used to plan a forthcoming project is Dyker Heights in Brooklyn. This neighborhood is served by a network of sewers constructed in the early 20th Century. While the system generally performs well, it can become quickly overwhelmed during heavier rain, resulting in sewers backing up into basements. DEP identified excess capacity in a nearby trunk main and through modeling showed that upsizing the street pipes that drain into that trunk main would be sufficient to capture the more intense rainfall New York City has been experiencing. This solution, estimated to cost more than $60 million for the construction of water mains and sewers, will relieve flooding for 14,300 residents in a 145-acre area. The project has been turned over to the Department of Design and Construction (DDC) for design.

This citywide hydraulic model will allow DEP to eventually create a “smart sewer” network by installing hundreds of sensors that will allow for the monitoring of stormwater flow levels in real-time. When combined with the future installation of gates and valves within the sewer system, DEP could use this sensor data to automatically divert stormwater flows from pipes that have reached capacity into others with excess room, thereby utilizing all available space in the network.

Hydraulic modeling is one of the many efforts DEP is undertaking as the agency develops plans to make New York City more resilient to extreme weather. Sewer capacity upgrades, green infrastructure, permeable pavement, bluebelts, cloudburst management projects, and data-driven maintenance are all tools the agency is implementing to manage stormwater, as outlined in the recently released 2024 Stormwater Analysis.

About the NYC Department of Environmental Protection

DEP manages New York City’s water supply, providing approximately 1 billion gallons of high-quality drinking water each day to nearly 10 million residents, including 8.5 million in New York City. The water is delivered from a watershed that extends more than 125 miles from the city, comprising 19 reservoirs and three controlled lakes. Approximately 7,000 miles of water mains, tunnels and aqueducts bring water to homes and businesses throughout the five boroughs, and 7,500 miles of sewer lines and 96 pump stations take wastewater to 14 in-city treatment plants. DEP also protects the health and safety of New Yorkers by enforcing the Air and Noise Codes and asbestos rules. DEP has a robust capital program, with a planned $29 billion in investments over the next 10 years. For more information, visit nyc.gov/dep, like us on Facebook, or follow us on X, formerly known as Twitter.