US Geological Survey

Resource Management Evaluation and Study of Saltwater Movement Within the Transition Zone of the Hudson River Estuary, New York (NY 88-175)

Table of Contents

PERIOD OF PROJECT: May l988 through present

PROJECT LEADER: M. Peter de Vries

FIELD LOCATION: Lower Hudson River basin, New York (map, photo)


New York City Department of Environmental Protection, New York State Department of Environmental Conservation, Hudson Valley Regional Council (representing Dutchess, Orange, Putnam, Rockland, Ulster, and Westchester Counties), and New York State Department of Health


The effect of major freshwater withdrawals on salinity in the transition zone of the Hudson River is unknown. Increased salinity and upstream movement of the salt front could adversely affect wildlife habitats and water supplies. As a result, new water supplies cannot be developed until their probable effect on saltwater movement can be determined.


(a) To identify and describe the forces that determine the location and shape of the salt front, (b) identify the effect of seasonal variations and channel geometry on the location of the salt front, and (c) predict the effect of water withdrawals at different points on the location of the salt front.


This study is divided into several phases that include: (a) identifying and evaluating present models, data, and data-collection programs; (b) installing tide-stage and water-quality stations at several locations; (c) performing tidal-cycle discharge and salinity measurements under differing hydrologic conditions; (d) using these data to calibrate and verify models to simulate the forces that control flow and saltwater movement in the estuary; and (e) evaluating several water-withdrawal plans with these models.


Continuous-record water-quality (specific conductance, water temperature) and tide-stage gages are operated at Hastings-on-Hudson, West Point, and just below Poughkeepsie. Freshwater inflow is measured at several tributaries. This record describes the seasonal movement of the salt front and provides boundary conditions for digital models. Fifty-eight boat runs were made to delineate the longitudinal variation of chloride concentration during high-slack tide conditions; 10 boat runs were made during low-slack tide conditions. The salt front (100 milligrams per liter of chloride) ranges from below Hastings-on-Hudson to New Hamburg during most years, but can move as far north as Poughkeepsie (which uses the Hudson as a drinking water source) during periods of drought. Ten 24-hour tidal-cycle discharge and chloride-concentration-profile measurements were performed, each of which entailed more than 100 discharge measurements in the cross section and provided detailed horizontal and vertical velocity, and specific conductance profiles. Results show measured discharge rates as high as 370,000 ft3/s (cubic feet per second) at Tellers Point near Ossining. Chloride concentrations indicate that the transition zone of the estuary is partly mixed in some areas and behaves as a salt wedge in others. Data are to be included in the USGS National Water-Information System. A GIS data base, including digital elevation and bathymetric data has been developed and interfaced with the models. The one-dimensional Branch flow model has been calibrated for the 133 mile reach from Hastings-on-Hudson to Green Island. The one-dimensional solute transport model (BLTM) has been used to observe model response to withdrawal scenarios. The study makes important real-time and historical information available for use by local, State, and Federal agencies, scientists, civil engineers, students, and the news media (critical during dry periods in 1988, 1991, 1993, 1995, and 1999).

POINTS OF CONTACT (mail, tel, WWW address)

Further information may be obtained from the Information Specialist of the U.S. Geological Survey at 425 Jordan Rd. Troy, NY 12180, telephone (518)285-5602, or Internet address <>. Selected data and information are available at the USGS Hudson River Salt Front Study Home Page.

U.S. Department of the Interior, U.S. Geological Survey
Maintainer: New York District
Last update: 15:31:41 Monday 14 January 2013
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