Catskill Aqueduct

The Catskill Aqueduct, part of the New York City water supply system, brings water from the Catskill Mountains to Yonkers where it connects to other parts of the system.

History
Construction commenced in 1907. The aqueduct proper was completed in 1916 and the entire Catskill Aqueduct system including three dams and 67 shafts was completed in 1924. The total cost of the aqueduct system was $177 million.

Specifications
The 92 mi aqueduct consists of 55 mi of cut and cover aqueduct, over 14 mi of grade tunnel, 17 mi of pressure tunnel, and nine miles (10 km) of steel siphon. The 67 shafts sunk for various purposes on the aqueduct and City Tunnel vary in depth from 174 to 1187 ft. Water flows by gravity through the aqueduct at a rate of about 4 ft/s.

The Catskill Aqueduct has an operational capacity of about 550 e6USgal per day north of the Kensico Reservoir in Valhalla, New York. Capacity in the section of the aqueduct south of Kensico Reservoir to the Hillview Reservoir in Yonkers, New York is 880 e6USgal per day. The aqueduct normally operates well below capacity with daily averages around 350–400 e6USgal of water per day. About 40% of New York City's water supply flows through the Catskill Aqueduct.

Geography
The Catskill Aqueduct begins at the Ashokan Reservoir in Olivebridge, New York, located in Ulster County. From the Ashokan Reservoir, the aqueduct traverses in a southeasterly direction through Ulster, Orange, and Putnam counties. It tunnels first beneath the Rondout Valley and Rondout Creek in the town of Marbletown, then beneath the Wallkill River in the town of Gardiner in Ulster County before flowing toward Orange County, New York. It crosses 1100 ft below the Hudson River bed at Storm King Mountain in Orange County before reaching Putnam County on the east side of the river at Breakneck Mountain. The aqueduct transports water from Ashokan as well as the Schoharie Reservoir, which feeds into Ashokan.

The aqueduct then enters Westchester County, New York, and flows to the Kensico Reservoir, which also receives water from the city's Delaware Aqueduct. It continues from the Kensico reservoir and terminates at the Hillview Reservoir in Yonkers. The Hillview Reservoir then feeds City Tunnels 1 and 2, which bring water to New York City. If necessary, water can be made to bypass both reservoirs.