Using Hydrologic Forecasts for Dynamic Management of New York City's Reservoir Releases for the Delaware River Basin

The New York City Department of Environmental Protection (DEP) has initiated design of the Operations Support Tool (OST), a state-of-the-art decision support system to provide computational and predictive support for water supply operations and planning. Using an interim version of the OST, DEP and the Delaware River Basin Decree Parties (the states of New York, New Jersey, Pennsylvania, and Delaware) have developed a forecast-based reservoir release program to succeed the prior Flexible Flow Management Program (FFMP) which expired on May 31, 2011.

The original FFMP grew out of the Good Faith Agreement of 1983 among the four Basin states that established modified water supply diversions and stream flow targets during drought conditions. It provided a set of release schedules as a framework for managing diversions and releases from New York City's Delaware Basin reservoirs in order to support multiple objectives, including water supply, drought mitigation, flood mitigation, tailwaters fisheries, main stem habitat, recreation, and salinity repulsion. The forecast-based program (known as “OST-FFMP”) defines Upper Delaware reservoir releases based on an expanded set of release schedules and a forecast-based estimation of water availability. Additionally, the OST-FFMP attempts to provide enhanced downstream flood protection by making spill mitigation releases to keep the Delaware System reservoirs at a seasonally varying conditional storage objective.

The OST-FFMP approach represents a more robust way of managing downstream releases, accounting for predicted future hydrologic conditions by making more water available for release when conditions are forecasted to be wet and protecting water supply reliability when conditions are forecasted to be dry. Further, the dynamic nature of the program allows the release decision to be adjusted as hydrologic conditions change. OST simulations predict that this program can provide substantial benefits for downstream stakeholders while protecting DEP's ability to ensure a reliable water supply for 9 million customers in NYC and the surrounding communities. Initial performance of the program (instituted starting on June 1, 2011) has been positive, providing increased releases from NYC's reservoirs to meet downstream objectives and providing NYC an analytical basis for quantifying risk to water supply. This paper will describe the OST-FFMP program and discuss preliminary observations on its performance based on key NYC and downstream stakeholder performance metrics.