USGS - science for a changing world

National Water Census

Dept. of Interior WaterSMART activities

Dept. of Interior WaterSMART activities

Delaware River Basin

Map of Delaware River Basin. - click to enlarge
Map of Delaware River Basin. - click to enlarge
The Delaware River Basin covers 13,500 square miles in parts of four States, including New York, New Jersey, Pennsylvania, and Delaware. The population in the basin is approximately 7.3 million people. The basin has the largest inter-basin withdrawal of water east of the Mississippi River and provides water to over 15 million people. After a history of litigation, many of the water management decisions on the river system are now coordinated through an interstate river basin commission known as the Delaware River Basin Commission (DRBC). In the upper portions of the basin, concerns over the effects of new natural gas development and the freshwater requirements for a recently-discovered endangered mussel species have added new complexities to water management in the basin.

The USGS Water Census Focus Area Study in the Delaware Basin will concentrate on providing information to stakeholders in the basin, and will contribute to science needs outlined in the DRBC water management strategy. Among the needs identified by over 60 stakeholder groups, including Federal, State, local, NGOs, academics, and others was the importance of improving the integration of water-use and water supply data. Stakeholders also pointed out the need for a scientific approach to defining relations between streamflow processes and the responses of aquatic organisms in tributary streams. Finally, stakeholders recognized the usefulness of a hydrologic watershed model to evaluate water stressors such as growth of population centers, the effects of land-use change, and the effects of climate variability and change on water resources in the basin.

Based on this feedback, USGS will develop the following information products as part of the Delaware Focus Area study:

Improved water-use and water-supply information

Each state in the Delaware River Basin collects slightly different water use information and has different reporting thresholds. For the water census the USGS will provide quality-assured and consistent water use estimates across the basin. This will include site specific information, such as surface-water diversions and withdrawals, groundwater withdrawals, and surface-water return flows. From this data, median monthly, seasonal, and yearly water use estimates will be developed. Instream use data for hydroelectric power will also be compiled and estimates for unreported water uses, such as domestic, irrigation, livestock, and mining, will be developed. Water-use data will be compiled at a 12 digit hydrologic unit code sub-basin level (HUC-12) for use by modelers, ecologists, and others conducting water assessments in the basin. Methods will be published and information will be available to the public via a web-based application.

Water Use Contact: Kristin Linsey, 518-285-5636,

Develop a surface-water hydrologic model of the Delaware Basin capable of evaluating impacts of land-use change, climate change, and changes in water demand

The Water Availability Tool for Environmental Resources (WATER); Williamson and others, 2009) will be used to develop a streamflow model that encompasses the non-tidal Delaware River Basin. The model will be used as a decision support tool to evaluate how water stressors such as population growth, land-use change, climate variability, and climate change affect the availability of water resources in the basin. WATER will be validated using precipitation, water-use, streamflow, and other information for the time period 2001 to 2011. Simulations of future streamflow and water-availability conditions centered on 2030 and 2060 will incorporate projected changes in water use, land use, and climate in the watershed. Model results will be published and the model will be available to the public.

  • More information on the Delaware Basin WATER hydrologic flow model can be found by clicking here.

WATER Model Contact: Tanja Williamson, 502-493-1934,

Developing ecological-flow science in tributaries

Tributaries in the Delaware River Basin will be studied to define relations that exist between major components of streamflow (magnitude, durations, frequency, timing, and rate of change) and the response of aquatic assemblages (ecological flows). This information will assist managers in making decisions about meeting human water needs while maintaining healthy ecological communities in streams. The study will compile fish and invertebrate data from state, federal, and other agencies, and develop common taxonomic levels for analysis. A flow model (QPPQ) will be used to estimate daily mean streamflow for ungaged locations in the basin using map correlation to nearby gaged sites. Flows will be estimated from 1960 to 2011. Based on this data, and results from the WATER model, streams will be classified, and flow and aquatic assemblage response relations will be developed for sites with ecological data. Using these relations, and future flow predictions from the WATER model, assessments can then be made of how aquatic communities might respond to future changes in flow. Results will be published in reports and the QPPQ model will be available to the public.

Contact for Ecological Analysis - Jonathan Kennen, 609-771-3948,
Contact for Estimating Streamflow - Marla Stuckey, 717-730-6950,

Developing Ecological-Flow Science on the main-stem of the Delaware River

Flow on the main-stem of the Delaware River is controlled, to a large extent, by waters released from New York City (NYC) drinking water reservoirs and power-supply reservoirs. Releases from the NYC reservoirs are regulated to meet a variety of needs, including water supply demands, protection of downstream fisheries habitat, and to repel the upstream movement of salt water in the Delaware Estuary. To meet these competing needs the basin states, the City of New York, the Federal Government, and the DRBC have developed a Flexible Flow Management Plan (FFMP). One of the management goals of the FFMP is to protect the cold water fishery while maintaining aquatic community diversity, structure, and function through improved ecological flow releases on the Delaware River. Unfortunately the relationship between flows, environmental variables (such as temperature), and ecological response are not well understood. Thus, the Water Census study on the main-stem of the Delaware River is designed to determine the ecological flow needs of a variety of freshwater species such as fishes, mussels and submerged aquatic vegetation in the Upper Delaware River Basin. This information will be incorporated into a Decision Support System (DSS) that will allow managers to evaluate how different flow scenarios might affect the amount of habitat that is available for each species. Upon completion the study results will be published and the DSS will be made available to users.

  • More information on the study and the DSS can be found by clicking here.

Contact for Main-stem Ecological work: Heather Galbraith, 570-724-3322 x230,


Cole, J.C., Maloney, K.O., Schmid, M. and McKenna Jr, J.E.. 2014. Developing and testing temperature models for regulated systems: A case study on the upper Delaware River. Journal of Hydrology. v519: 588- 598.

Hutson, S.S., Linsey, K.S., Ludlow, R.A., Reyes, Betzaida, and Shourds, J.L., 2016, Estimated use of water in the Delaware River Basin in Delaware, New Jersey, New York, and Pennsylvania, 2010: U.S. Geological Survey Scientific Investigations Report 2015–5142, 76 p.,

Maloney, K.O., Cole, J.C., Schmid, M., 2016. Predicting thermally stressful events in rivers with a strategy to evaluate management alternatives. River Research and Applications. 32(7). 1428-1437.

Talbert, Colin, Maloney, K.O., Holmquist-Johnson, C.L., and Hanson, Leanne, 2014, User’s manual for the upper Delaware River riverine environmental flow decision support system (REFDSS), Version 1.1.2: U.S. Geological Survey Open-File Report 2014–1183, 23 p.,

Dissolved Methane in Groundwater, Upper Delaware River Basin, Pennsylvania and New York, 2007-12. By William M. Kappel.

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