The Croton Watershed is a term describing a part of the New York City water supply system (map here). It is not synonymous with the biological feature Croton River watershed. Numerous small natural lakes and ponds, as well as large Lake Mahopac, are within the river's watershed but not a direct part of the NYC water supply system. They are not owned or maintained by the New York City watershed system, but ultimately drain into it.[e]
Further, the drainage basins of the Boyds Corner and the West Branch reservoirs fall within the Croton River watershed but do not end up delivered to New York City in the waters of the Croton Watershed. Though the waters of those basins are collected within their respective reservoirs, Boyds Corners drains into West Branch, which then receives the entire flow of the NYC system's Delaware Aqueduct. After mixing and settling, the combined waters of these watersheds on both sides of the Hudson River continue on via the balance of the Delaware Aqueduct to the Kensico Reservoir; there they are joined by those of the Catskill Aqueduct, settle, then continue on to the Hillview Reservoir in Yonkers for distribution in New York City. Only overflow from West Branch Reservoir's spillway, composed predominantly of Delaware Aqueduct waters, continues on a downstream section of the West Branch Croton River, thence into the tandem of the Croton Falls Reservoir-Diverting Reservoir, and downstream from them ultimately into the New Croton Reservoir and the New Croton Aqueduct into New York City.
The waters of the West Branch are first dammed and held by the Boyds Corner Reservoir, which drains into the West Branch Reservoir. There they are joined by the flow of the Delaware Aqueduct, and after mixing and settling continue via it to the Kensico Reservoir. Only overflow crossing the West Branch Reservoir's spillway continues as a resumption of the West Branch Croton River downstream of it. This flows into the Croton Falls Reservoir, which also receives the entire flow of the Middle Branch Croton River via the Middle Branch Reservoir lying immediately upstream of it.
The Croton Falls Reservoir also receives part of the flow of the East Branch Croton River from the Diverting Reservoir built downstream of the East Branch Reservoir and Bog Brook Reservoir (via a channel and dividing weir linking the Croton Falls and Diverting reservoirs allowing water to freely pass between them, and comingling waters of all three branches in both). A separate outflow from the Diverting Reservoir also drains into the continuation of the East Branch. Both the West and East Branches continue south separately before joining to end the northern half of the New York City water system's Croton Watershed and form the Croton River proper.
12The land areas are the same, but their drainages are not coterminous. Numerous small natural lakes and ponds, as well as large Lake Mahopac, are part of the Croton River's watershed but not a direct part of the NYC water supply system - though all of their outfalls drain into streams or rivers captured by the system.
↑Including dams, spillways, tunnels, pumps, and related mechanical components not part of a hydrological drainage basin.
↑Less waters from the drainage basins of the Boyds Corner and the West Branch reservoirs, which are mixed in West Branch with the flow of the NYC system's Delaware Aqueduct and after settling carried on by the aqueduct to the Kensico Reservoir.
↑86.6billion US gallons (328,000,000m3) in reservoirs, roughly 5.5billion US gallons (21,000,000m3) in controlled lakes, and 7.5billion US gallons (28,000,000m3) in its river system.
↑Lake Mahopac, which features a sluice gate at its extreme southwestern corner, is an auxiliary water source for the New York City system.[4]
↑Administrative Code of New York City, The New York City, Chapter 3, Water Supply, American Legal Publishing: According to Title 24 (Environmental Protection and Utilities) of the New York City Administrative Code, Chapter 3 (Water Supply), Subchapter 1 (Water Supply to the City of New York), Section 24-328 (Lake Mahopac; level of water not reduced): "Nothing in this chapter contained shall authorize, empower or permit any water in excess of its ordinary flow to be drawn from Lake Mahopac, in the town of Carmel, Putnam county, between the first days of March and September in any year." Drawing on the Lake between September 2nd and the last day of February in any given year is not therein proscribed.
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