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|  StormwaterStormwater is generated from rain and melting snow which is conveyed over impervious surfaces such as rooftops, streets, and sidewalks. Rather than being absorbed into the ground, much of the stormwater in New York City flows over impervious surfaces into roof drains or catch basins in the streets, and from there into the sewers. These impervious surfaces cover approximately 72% of New York City’s 305 square miles in land area and generate a significant amount of stormwater. Stormwater can pose challenges to the City in the form of combined sewer overflows and flooding. This section describes how stormwater is conveyed through the City, the challenges it creates, and what the City is doing overcome them. | |
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 Types of Sewer Drainage Areas in New York City In New York City, stormwater is conveyed through combined sewers or separate sewer systems. In unsewered areas, water flows directly over the ground into waterways.  Learn more |
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Combined Sewer Overflows (CSOs) Sometimes, during heavy rain and snow storms, combined sewers receive higher than normal flows. Treatment plants are unable to handle flows that are more than twice design capacity and when this occurs, a mix of excess stormwater and untreated wastewater discharges directly into the City’s waterways at certain outfalls. This is called a combined sewer overflow (CSO). We are concerned about CSOs because of their effect on water quality and recreational uses. Learn more |
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Flooding in New York City A look at the areas prone to flooding, the causes of flooding in New York City, and what residents can do to help protect our City from flooding. Learn more |
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Using Green Infrastructure to Manage Stormwater DEP has a broad citywide effort to better manage stormwater using a variety of innovative, sustainable green infrastructure. Learn more |
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Guidelines for the Design and Construction of Stormwater Management Systems DEP has published Guidelines for the Design and Construction of Stormwater Management Systems. Learn more |
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