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USGS Water Science Centers are located in each state.

Summary of August 2011 Monthly Hydrologic Conditions

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

August 2011

August 2011 was the wettest month on record in New Jersey. On average there was 16.64 inches statewide which is 4.66 inches more then the second wettest month on record in October 2005. This is 12.43 inches above the 1981-2010 monthly average of 4.21 inches. Despite below average precipitation in June and July, the precipitation in August made the summer of 2011 the wettest season on record in New Jersey. There was 23.90 inches of precipitation, which is 4.23 inches above the previous season record of 19.67 inches in 1928.

Precipitation was above normal at all three index stations. Newark reported 18.79 inches, which is 467 percent of normal.  Atlantic City reported 11.11 inches, which is 257 percent of normal.  Trenton reported 16.10 inches, which is 424 percent of normal. Total precipitation over the past 12 months was: 61.07 inches at Newark, which is 14.82 inches above normal; 48.03 inches at Atlantic City, which is 7.44 inches above normal; and 55.56 inches at Trenton, which is 14.17 inches above normal.

Observed rainfall from August 1 through August 26th ranged from 8 inches to over 16 inches, 150 – 600 percent of normal, in a band from southwestern through central New Jersey. Heavy rain associated with a low pressure system moving northeast along the Atlantic coast dropped generally 4 – 8 inches of rain over most of the state from late Saturday night August 13 through late Sunday night August 14, 2011. Hurricane Irene moved up the eastern seaboard making landfall for a second time at Little Egg Inlet New Jersey early Sunday morning August 28, 2011. This is the first time a Hurricane made landfall in New Jersey since 1903. Heavy rain spread north across the state from Saturday morning through Saturday afternoon. Rain continued for about an 18 hour period through Sunday morning. From 6-7 inches fell across most of the state. Higher amounts from 7 inches to as much as 10 inches were observed at USGS and NWS gages.

Combined storage in the thirteen major water supply reservoirs as of August 31 was 80.460 billion gallons (99.5 percent of capacity), which is higher than the average August contents for the reference period 1961-1990.  The storage was 8.494 billion gallons higher than one month ago and 27.471 billion gallons higher 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, Charlotteburg Reservoir, Echo Lake, Wanaque Reservoir and Spruce Run Reservoir.                                              

Streamflow was higher than the long-term monthly-mean for the reference period 1971-2000 at all three index stations. The monthly-mean discharge at South Branch Raritan River near High Bridge was 333 ft3/s, 442 percent of the long-term mean; breaking the previous record of 285 ft3/s set in 1942.  The maximum daily mean discharge was 4,760 ft3/s, breaking the previous record of 1,860 ft3/s for August set in 1955. The monthly-mean discharge of the Great Egg Harbor River at Folsom was 299 ft3/s, 508 percent of the long-term mean; breaking the previous record of 182 ft3/s set in 1967. The maximum daily mean discharge was 1,260 ft3/s, breaking the previous record of 695 ft3/s for August set in 1933. The monthly mean discharge of the Delaware River at Trenton was 25,000 ft3/s, 454 percent of the long-term mean. The observed daily mean discharge of the Delaware River at Trenton on August 31 was 65,300 ft3/s. 

New Jersey experienced record flooding at USGS gages during the month of August. Gages on the Cohansey River and Little Ease Run had record peaks on August 14. The second and third highest peaks of record occurred at other gages in southwestern New Jersey during the period August 14-16, 2011. Record peaks were recorded statewide from August 28 - 31. Thirty-eight of the 93 gages with greater than or equal to 20 years of record had record high peaks. Another 24 gages recorded the second highest peaks of record and 5 gages recorded the third highest peaks of record. Thirty gages experienced peaks greater then the 100 year recurrence interval (< 1.0% annual exceedance probability). Ten of these gages experienced greater than a 500 year event (< 0.2 % annual exceedance probability).

Groundwater levels, as measured in water-table observation wells for the month of August, were above normal at all three index wells. Levels increased from last month, and were higher than one year ago.  Readington School 11 index well was 10.12 ft higher than last month and 12.88 ft higher than last year. Morrell 1 index well was 3.44 ft higher than last month and 4.96 ft higher than last year. Vocational School 2 index well was 2.87 ft higher than last month and 2.21 ft higher than last year.

Water-quality parameters collected from the Delaware River at Trenton were within recorded historical monthly extremes. Water temperature ranged from 18.2 to 28.6 degrees Celsius. Dissolved oxygen ranged from 7.3 to 9.2 milligrams per liter. Specific conductance ranged from 84 to 255 microsiemens per centimeter at 25°C.

Also see the August report from the State Climatologist.

Note: The preceding data is preliminary and subject to revision.

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