Department of Environmental Conservation

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Reservoir Releases

"It is hereby declared to be the public policy of the State of New York that the waters of the state be conserved and developed for all public beneficial uses" (Environmental Conservation Law § 15-0105).

What are Reservoirs?

Photograph of the Cross River Spillway in Westchester County
Cross River Spillway, Westchester County

Reservoirs are structures used to help "conserve and develop" water resources. In a reservoir, water from a stream or river is stored behind a dam for various beneficial uses, like drinking water supply, electrical generation, recreation, irrigation or to protect and enhance wildlife habitat. When full, water flows through and safely out of a reservoir through a specially designed spillway. In New York, many reservoirs are relatively small structures used primarily for agricultural purposes, whereas, larger reservoirs are used primarily for water supply. Many are also popular as recreational sites for fishing and water sports.

New York Reservoir Release Regulations

New York Reservoir Release Regulations are found in Title 6 of New York Code, Rules and Regulations Parts 670 through 672. These regulations cover reservoirs having a capacity of more than one billion gallons in the counties of Delaware, Greene, Putnam, Schoharie, Sullivan, Ulster and Westchester. While reservoirs are useful for a variety of purposes, they also alter natural stream flow which can impact wildlife habitat or public beneficial uses. To help offset these impacts, releases of water from reservoirs may be made through specially designed outlet mechanisms. A goal of New York reservoir release regulations is to enhance recreational uses, such as trout fishing and canoeing, of waters affected by reservoir releases while ensuring and without impairing an adequate supply of water for power production or for any municipality which uses water from such reservoirs for drinking and other purposes.

Are Reservoirs the Same as Flood Control Dams?

While they both involve dams, reservoirs are not flood control dams. Whereas flood control dams are specially designed to remain largely empty to capture major runoff events, reservoirs are designed to remain largely full, reserving water for later uses. However, reservoirs can and do provide some flood protection benefits, because even when full, they reduce downstream peak flow rates during large runoff events.

The Department continues to examine options for reservoir "voids" that maintain water supply system reliability, but provide improved potential for flood mitigation. When considering potential options, the Department is mindful of standard operational practices for water supply reservoirs. Reservoirs typically refill with runoff from spring rains and snowmelt, then are drawn down during the rest of the year when withdrawals may exceed natural inflow. Releases from reservoirs are made with the goal of being full at the start of the reservoir drawdown period (around June 1st) to assure an adequate supply of drinking water for human uses. Releases made to create a "void" for spill mitigation purposes during the refill period increases the likelihood that the reservoir will run dry.

graph to demonstrate peak flood stage observed downstream

During high flow periods, full reservoirs attenuate tailwater flows during a storm event and will tend to reduce the peak flood stage observed downstream (see graph on the left). The presence of available storage (a "void") will further attenuate downstream flows. However, drinking water reservoirs are not designed as flood control structures to protect against floods. They tend to be small compared to the watershed they impound and have smaller release works than flood control structures. Therefore, they are not able to release large quantities of impounded water in advance of forecasted storms.

As such, the Department is wary of leading those in flood risk areas to believe that reservoirs provide suitable flood protection. Flood plain controls which require new and substantially improved structures to be elevated above the one percent chance flood elevation do more to protect at-risk properties than any conceivable reservoir management scenario.

New York State has over 100 flood control projects. More can be learned about the DEC dam safety and flood protection programs from the Bureau of Flood Protection and Dam Safety.

More about Reservoir Releases

Ashokan Reservoir
Ashokan Reservoir.

New York State, in consultation with New York City, participates with Delaware, New Jersey, Pennsylvania and the Federal government in the Delaware River Basin Commission (DRBC), see Links Leaving DEC's Website in right hand margin. The members of the DRBC are the four state governors and a presidential appointed federal government representative. The DRBC strives to conserve and protect water resources and improve water use in the Basin for the benefit of the Basin as a whole. Releases from the New York City Delaware Basin Reservoirs (Cannonsville, Neversink and Pepacton) are a major component of the Upper Delaware River system.

More about Reservoir Releases:

  • New York's Role in the Delaware River Basin Commission (DRBC) - Representing New York in a Federal-Interstate Commission.
  • New York City Water Supply System - New York City's water supply system includes the following reservoirs: Cannonsville, Pepacton, Schoharie, Ashokan, Rondout, and a number of reservoirs in the Croton Reservoir System. There are also 69 wells located in Queens, N.Y.
  • Ashokan Reservoir - New document for Interim Protocol to provide regular water releases from Ashokan Reservoir supporting habitat and discharge mitigation releases. NYSDEC is requesting comments.
  • Water Releases for Esopus Creek - Historically, the Department has received requests from a consortium of recreational groups that hold recreational water events. These groups coordinate scheduling with other planned boating events throughout the region. Requests for diversions for special recreational events must be received in writing by April 15th of each year.
  • About Delaware Basin Reservoir Releases - Questions about reservoir releases