April 30, 2015

Contact:

deppressoffice@dep.nyc.gov, (845) 334-7868

Delaware River Basin Commission Releases Updated Water Resource Planning Model

The Delaware River Basin Commission (DRBC) today announced the release of an updated modeling tool that will allow the public to test water management scenarios and compare their outcomes.  The tool, known as the Delaware River Basin-Planning Support Tool (DRB-PST), provides interested stakeholders with the ability to test flow management scenarios against a set of existing targets, regulations, and laws that govern the use of water within the Delaware River Basin. The tool will show users how those scenarios would change an array of outcomes, including the amount of water available for drinking supplies, downstream releases, habitat protection, flood mitigation, and more.

"The availability of the DRB-PST modeling tool is a positive development intended to support a more comprehensive understanding about how reservoir and flow management operating plans affect river flows and related aquatic habitats," said DRBC Executive Director Steve Tambini. "It will allow interested stakeholders to use a science-based tool to compare the impacts of ‘what-if' scenarios on multiple and complex water resource goals, targets and objectives."

River flows, diversions out of the basin, and water uses within the basin are managed, operated and regulated through a series of complex and interdependent rules and targets. The DRB-PST model uses hydrologic inputs (like runoff and snowmelt), operating conditions, and management rules to help evaluate the impacts of reservoir operating plans on the multipurpose water resource objectives identified in the Delaware River Basin Compact, which created the DRBC in 1961.

Three reservoirs located in headwaters of the Delaware River that are owned and operated by the City of New York (NYC) provide about half of the city's water supply. Downstream releases of water from these reservoirs and diversions out of the basin for NYC and New Jersey were established and continue to be negotiated by Delaware, New Jersey, New York, Pennsylvania, and NYC (commonly known as "the Decree Parties") under the terms of a 1954 U.S. Supreme Court Decree and the subsequent Good Faith Agreement Recommendations.

The DRBC and the Decree Parties have some overlapping membership and a long history of collaboration on planning and modeling issues within the Delaware River Basin. The DRBC signatory members include the four basin states and the federal government. NYC is not a DRBC member. The Compact prohibits the DRBC from adversely affecting the releases or diversions provided in the 1954 Decree without the unanimous consent of the five Decree Parties.

The Flexible Flow Management Program (FFMP), which has been unanimously approved by the Decree Parties, is intended to meet water supply demands, protect fisheries habitat downstream of the NYC-Delaware Basin reservoirs, enhance flood mitigation, and repel the upstream movement of salt water in the Delaware Estuary. The FFMP's target numbers and goals are included in the PST-DRB model and any changes to the FFMP in the future can be reflected in the model as well.

The DRBC's original water supply planning model was developed in 1981. That model was revised several times to include additional data, facilities, and flow management policies, and was moved into OASIS software in the early 2000s. The original OASIS model known as DRB-OASIS can simulate the current FFMP, including the Combined Seasonal Storage Objective (CSSO) for flood mitigation, but not the revised Habitat Protection Program (HPP) which has evolved since the first FFMP. The Habitat Protection Program uses simulated forecasts of reservoir inflows to determine the amount of water available for fisheries releases from the three NYC reservoirs. In doing so, modeling can be performed to evaluate scenarios that use water more efficiently for fisheries habitat objectives while maintaining the reliability of critical water supply objectives and flood mitigation components of the FFMP.

The DRB-PST incorporates aspects of NYC's Operations Support Tool (OST), a sophisticated monitoring and modeling system that allows for better predictions than previous tools of reservoir-specific water storage levels, quality, and inflows. OST uses forecasts to determine the amount of available water to release for habitat protection and assesses the risks of reservoir operations to public water supply needs across the entire NYC reservoir system, not only its three Delaware River Basin reservoirs. DRB-PST incorporates the OST simulated forecasts for long-term water supply planning based on reservoir operations. A technical working group from DRBC, the Decree Parties (four states and NYC), and the City of Philadelphia have worked together to ensure that the model is useful for those with an interest in Delaware River operations. This group will continue to evaluate and verify model inputs and results and release revised PST versions as necessary.

"Scientists and engineers from DRBC and New York City collaborated to ensure this new public modeling tool produced accurate results that are comparable to those generated by the OST modeling tool that the City uses to make decisions about reservoir operations every day," said Tambini.

Persons who did not previously use the DRB-OASIS model who wish to obtain the DRB-PST model for the first time will need to purchase required software. Additional information about DRB-PST and the upcoming Regulated Flow Advisory Committee meeting can be found on the commission's web site at www.drbc.net.

DRBC is a federal/interstate government agency responsible for managing the water resources within the 13,539 square-mile Delaware River Basin without regard to political boundaries. The five commission members are the governors of the basin states and the commander of the U.S. Army Corps of Engineers' North Atlantic Division, who represents the federal government. More information concerning the 1954 Decree, the Decree Parties, and related water management activities can be found on the web site for the USGS Office of the Delaware River Master at http://water.usgs.gov/osw/odrm/.