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Summary of September 2004 Monthly Hydrologic Conditions

Compiled in cooperation with the New Jersey Department of Environmental Protection
Provisional assessment of hydrologic conditions in New Jersey

The following pages are adapted for online release from a summary of hydrologic condions for the previous month.

September 2004

Precipitation was below normal at the Atlantic City index station, and above normal at Newark and Trenton index stations. Atlantic City reported 2.30 inches, which is 73.2 percent of normal. Newark reported 8.01 inches, which is 200 percent of normal. Trenton reported 7.70 inches, which is 225 percent of normal.

In addition to above average rainfall in the preceding months, on September 17 the remnants of Hurricane Ivan produced rainfall amounts ranging from 3 to 8 inches in northeastern Pennsylvania and southern New York. Flooding in the Delaware River Basin ensued for several days. As a result, the Delaware River at Trenton reached a new maximum historical monthly mean of 32,530 ft³/s, which is 506 percent of normal. The observed daily mean discharge of the Delaware River at Trenton on September 19 was 179,000 ft³/s; on September 30 it was 49,400 ft³/s. Details of the September 17-23 eventís effect on the Delaware River at Trenton can be found in the Flood Statement below.

Streamflow was also above normal at the HighBridge and Folsom index stations. The monthly-mean discharge at South Branch Raritan River near High Bridge was 150 ft³/s, 182 percent of normal. The monthly-mean discharge of the Great Egg Harbor River at Folsom was 66.8 ft³/s, 119 percent of normal.

Combined storage in the thirteen major water supply reservoirs as of September 30 was 76.7 billion gallons, which is 95.4 percent of capacity. The storage was 4.06 billion gallons more than one month ago and 3.16 billion gallons more than one year ago. The thirteen major water supply reservoirs are as follows: Lake Tappan, Woodcliff Lake, Oradell Reservoir, DeForest Lake, Splitrock Reservoir, Boonton Reservoir, Canistear Reservoir, Oak Ridge Reservoir, Clinton Reservoir, Charlottesburg Reservoir, Echo Lake, Wanaque Reservoir and Spruce Run Reservoir.

Groundwater levels, as measured in water-table observation wells, were above normal at all three index wells, with the Readington School 11 well reaching a new historic monthly maximum. Levels increased from last month at the Readington School 11 and Morrell 1 wells, and decreased from last month at the Vocational School 2 well. Levels were higher than one year ago at the Readington School 11 and Morrell 1 wells, and were lower than one year ago at the Vocational School 2 well.

For a second consecutive month, the observed specific conductance at the Delaware River at Trenton reached a new historic monthly minimum as a result of the peak flows from the September 17-23 event. Temperature and dissolved oxygen were within recorded historic monthly extremes.

Flood Statement: Sept. 17-23, 2004

Flood peaks along the main stem of the Delaware River were the highest since the flood of August 19, 1955. Peak flows at the five gaging stations between Montague and Trenton, NJ ranged from a 40- to 70-year event. Peak flows at stream gages on major tributaries to the Delaware River in New Jersey did not exceed a 12-year event, except on the Beaver Brook at Belvidere, which experienced a 50-year flood.

The flood peak on the Delaware River at Trenton, NJ was the fourth highest recorded since 1903. The peak flow of 201,000 ft³/s on Septmeber 19 at 2045 hours equaled approximately a 40-year recurrence interval flood. Flood-frequency statistics at this site are based on peak-flow data from 1913 through 2004 and an historical peak in 1903, as well as historic flood peak information from various reports. The peak discharge recorded for this flood was 128,000 ft³/s less than the peak flow for the period of record on August 20, 1955. The peak gage height recorded for this flood was 23.29 ft, 5.21 ft less than the previous record of 28.60 ft set on August 20, 1955.

All of the files listed below are in Portable Document Format (PDF) which can be viewed/printed with the Adobe Acrobat® Reader, freely available for most computer platforms.

• Combined Storage in the 13 Major Water Supply Reservoirs
• Monthly precipitation at three selected sites
• Groundwater levels in selected Water-table observation wells
• Streamflow at selected sites
• Water quality for the Delaware River at Trenton