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How DEP Forecasts & Maintains Reservoir Levels

Reservoir Operations and Watershed Monitoring

The Catskill/Delaware system supplies the vast majority of New York City's water. Forecasting reservoir levels in this system is one of the most important and most difficult tasks DEP faces in the operation of the water supply. Reservoir levels are primarily determined by the balance between streamflow into the reservoirs, diversions (withdrawals) for water supply, and releases to maintain appropriate flows in the rivers below the dams. Streamflow is affected by rain and snowmelt, both of which are hard to predict accurately. DEP is harnessing new technology and a variety of resources to better predict and manage our water supply.

Water in the Delaware River Basin is jointly managed pursuant to a 1954 Supreme Court decree that governs water allocations for New York City and the states of New York, Pennsylvania, New Jersey, and Delaware. The Flexible Flow Management Plan (FFMP) is intended to provide a more adaptive means for managing releases from the Cannonsville, Pepacton, and Neversink reservoirs by providing for releases based solely on the time of year and reservoir storage conditions.

Neversink Reservoir

Water Flow Management for the Delaware River Basin
DEP has developed a set of graphs and tables that summarize the model output data supporting each release decision for the Cannonsville, Pepacton and Neversink Reservoirs. The Flexible Flow Management Program (FFMP) is based on the Operations Support Tool (OST), the computerized decision support system developed and implemented by DEP.
OST-FFMP Summary (PDF)

Operations Support Tool
Operations Support Tool is the mathematical computer model that provides better information on when it is safe to release water without unnecessarily increasing risk to the public water supply. The OST-FFMP Summary is compiled through OST.
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Water System Safe Yield Calculation Report
This report provides a summary of the computation of the safe yield of the New York City Reservoir System.
Read the 2011 report (PDF)

Snow Pillows
The snow pillow is a device that measures the amount of water in the snowpack for a watershed area. Snowpack water is important to the water supply because melting snow drains into reservoirs. The snow pillows provide continuous, real-time data on snowpack water content, and is a major component to accurate modeling.
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Useful Links & Resources
Links to resources for weather forecasts, reservoir levels and more.
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Reservoir Levels

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