41°16′56″N 73°40′04″W / 41.282317°N 73.667908°W / 41.282317; -73.667908

Delaware Aqueduct, New York

The Delaware Aqueduct is an aqueduct in the New York City water supply system. It takes water from the Rondout, Cannonsville, Neversink, and Pepacton reservoirs on the west bank of the Hudson River through the Chelsea Pump Station, then into the West Branch, Kensico, and Hillview reservoirs on the east bank, ending at Hillview in Yonkers, New York.

The aqueduct was constructed between 1939 and 1945, and carries approximately half of New York City's water supply of 1.3 billion US gallons (4,900,000 m³) per day. At 13.5 feet (4.1 m) wide and 85 miles (137 km) long, the Delaware Aqueduct is the world's longest tunnel.^[1]

Reservoirs and watersheds

The Delaware Aqueduct carries water from the 95-square-mile (250 km²), 49.6-billion-US-gallon (188-million-cubic-metre) watershed^[2] using the Rondout, Cannonsville, Neversink and Pepacton reservoirs with the Delaware and Neversink tunnels. (The latter three reservoirs are within the Delaware River watershed. Rondout is considered by the New York City Department of Environmental Protection (NYCDEP) to be part of the Delaware system despite being firmly within the Hudson River watershed.)

Combined, the four reservoirs account for 1,012 square miles (2,620 km²) of watershed and 320.4 billion US gallons (1.2 billion cubic metres) of capacity, 890 million US gallons (3.4 million cubic metres) of which goes to the city — 50% of daily demand. All this water is fed from the Rondout to West Branch Reservoir in Putnam County (part of the Croton River watershed, which includes the flow of the upstream Boyds Corner Reservoir), then to the Kensico, and Hillview reservoirs in southern Westchester County, before continuing on to distribution within New York City.

Leak problems

Leaks were first discovered in the Delaware Aqueduct in 1988, with water losses up to 36 million US gallons (140,000 m³) per day. The city took many years to analyze the leak problem and devise a solution. In 2010 it announced a plan for a major repair project.^[3]

Repairs

The NYCDEP is building a 2.5-mile (4.0 km) Rondout-West Branch Bypass Tunnel beneath the Hudson River, which will allow it to bypass the leak. Construction began in November 2013. "The number's going to be $1.5 billion to do the entire program to make the fix," said Paul Rush, Deputy Commissioner of the NYCDEP. "About two-thirds of it, $1 billion, will actually go into constructing a bypass tunnel around the location with the most significant leakage in Roseton, and to do additional concrete grouting in the Wawarsing section."^[4]

The new bypass tunnel is the largest construction project in NYCDEP's history. Construction of the tunnel, 500 feet (150 m) under the Hudson, was completed in 2019.^[1] To complete the repairs the aqueduct was shut down temporarily in 2022. An additional shutdown is planned for October 2024 through spring 2025. Completion of the project is dependent on potential drought conditions and associated demand levels for water from the Delaware system.^[5][6]