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Summary of April 2005 Monthly Hydrologic Conditions

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

April 2005

Precipitation was below normal at the Newark and Atlantic City index stations, and above normal at the Trenton index station. Newark reported 3.43 inches, which is 87.5 percent of normal. Atlantic City reported 3.40 inches, which is 98.6 percent of normal. Trenton reported 4.70 inches, which is 131 percent of normal. Total precipitation over the past 12 months was 50.63 inches at Newark which is 4.38 inches above normal, 41.56 inches at Atlantic City which is 0.97 inches above normal, and 47.50 inches at Trenton which is 6.11 inches above normal.

The Delaware River experienced the worst flood in 50 years after an average of only 3.2 inches of rain fell in the upper Delaware Basin from April 2-3. Above average rainfall in the preceding month, reservoirs filled to capacity, and snow melt from the Pocono and Catskill Mountains contributed to the flooding on April 4, 2005.

The Delaware River at Trenton index station recorded a peak gage-height of 25.33 ft, the third highest since 1902. The April 4 peak at this gage was 3.27 ft less than the previous record of 28.60 ft set on August 20, 1955. The instantaneous peak flow of 242,000 ft³/s exceeded the 100-year recurrence interval flood, based on peak-flow data from 1913 through 2005 and an historical peak from 1903, as well as historic flood-peak information from earlier floods. The mean daily flow of 230,000 ft³/s on April 4 was a new record for the maximum daily flow for the month of April, and was the second highest daily mean recorded for the period of record at this gage. The April monthly mean discharge of the Delaware River at Trenton was 45,440 ft³/s, which is 210 percent of normal. The observed daily mean discharge of the Delaware River at Trenton on April 30 was 20,200 ft³/s. Details of the flood event can be found in the Summary of April 2-4, 2005, flooding in New Jersey.

Streamflow was above normal at the High Bridge and Folsom index stations. The monthly-mean discharge at South Branch Raritan River near High Bridge was 351 ft³/s, 167 percent of normal. The monthly-mean discharge of the Great Egg Harbor River at Folsom was 144 ft³/s, 119 percent of normal.

Combined storage in the thirteen major water supply reservoirs as of April 30 was 79.0 billion gallons, which is 98.2 percent of capacity. The storage was 0.81 billion gallons less than one month ago and 0.06 billion gallons less 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 at index wells, as measured in water-table observation wells, were below normal at Readington School 11, only slightly below normal at Morrell 1, and above normal at Vocational School 2. Levels decreased from last month at Readington School 11 and Morrell 1 wells, but increased from last month at the Vocational School 2 well. Levels were lower than one year ago at all three index wells.

The water quality monitor at the Delaware River at Trenton was damaged during the April 4 flood event. Data is not available this month.

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