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Water-Resources Investigations Report 51–75

Prepared in cooperation with the New Jersey Department of Environmental Protection

Flood of July 21, 1975 in Mercer County, New Jersey

By Stephen J. Stankowski, Robert D. Schopp, and Anthony J. Velnich

Thumbnail of and link to report PDF (16.4 MB)


Intense rainfall during the evening of July 20 and early morning hours of July 21, 1975 caused flooding of unprecedented magnitude in highly urbanized Mercer County, New Jersey. Over 6 inches (152 millimetres) of rainfall was recorded during a 10-hour period at Trenton, the capital of New Jersey. No lives were lost but damages to highways and bridges, to industrial, business, and residential buildings, to farmlands and crops, and to water supply systems were severe.

This report illustrates the magnitude of the flood and provides hydrologic data needed for planning and design to control or lessen damages from future floods. It includes discussions of the antecedent conditions and meteorological aspects of the storm; a description of the flood and comparison to previous floods; a summary of flood stages and discharges; a discussion of flood frequency; and photomosaics which show inundated areas. More than 200 high-water marks are described as to location and elevation above mean sea level.

First posted June 18, 2012

For additional information contact:
Director, New Jersey Water Science Center
U.S. Geological Survey
810 Bear Tavern Road, Suite 206
West Trenton, New Jersey 08628

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Stankowski, S.J., Schopp, R.D., and Velnich, A.J., 1975, Flood of July 21, 1975 in Mercer County, New Jersey: U.S. Geological Survey Water-Resources Investigations Report 51–75, 69 p.






Description of the flood

Summary of flood stages and discharges

Flood frequency

Flood-crest elevations

Station data

References cited

Aerial photographs of flooded areas

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