New Jersey Water Science Center
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Summary of Annual Hydrologic Conditions - 2004
Volume 1: Surface Water
Three gaging stations, located in north, south, and central New Jersey, are considered index stations for statewide streamflow conditions. The monthly mean discharges at the Great Egg Harbor River and Delaware River gages, for June and September respectively, were the highest for the period of record. Monthly mean discharges at South Branch Raritan River, Great Egg Harbor River, and the Delaware River index gages were above average for 5, 9, and 8 months, respectively, during water year 2004 (fig. 1). Monthly means were above average in October, November, December, July, and September at each gage. Annual mean discharge at each of these index gaging stations was above the annual mean for the period of record for the second consecutive year (fig. 2).
Streamflow at the index station in northern New Jersey (South Branch Raritan River near High Bridge) averaged 156 ft3/s for the water year, which is 128 percent of the 1919-2004 average. Peak flow for the water year was 2,310 ft3/s on December 11; the recurrence interval is less than 5 years. The lowest daily mean flow was 36 ft3/s, recorded on July 11, which is about the 90-percent flow duration.
Streamflow at the index station in southern New Jersey (Great Egg Harbor River at Folsom) averaged 102 ft3/s, which is 120 percent of the 1926-2004 average. Peak flow for the water year was 389 ft3/s on February 9; the recurrence interval is from 2 to 5 years. The lowest daily mean flow was 37 ft3/s, recorded on July 11, which is about the 90-percent flow duration.
The observed annual mean discharge for the Delaware River at Trenton was 18,190 ft3/s, which is 155 percent of the 1913-2004 average. Peak flow for the water year was 201,000 ft3/s on September 19, and the recurrence interval is about 50 years. The lowest daily mean flow was 3,570 ft3/s, recorded on July 4, which is about the 85-percent flow exceedance. The Delaware River is substantially regulated by reservoirs and diversions.
Annual mean discharges for water year 2004 at 46 selected gaging stations that had 40 years or more of continuous record and mean annual discharge for the period of record at each gaging station are shown in table 1. The differences are listed as percent difference. Discharge at 45 of the 46 gaging stations was above normal for water year 2004. The percent differences ranged from -13.3 to 113.5. Discharge at 45 of the 46 gaging stations was above normal for water year 2003, and the percent differences ranged from -7.1 to 61.0. In contrast, during water year 2002, flow at all 46 gaging stations was well below normal with the percent differences ranging from -38.6 to -94.4. Discharge at 40 of the 46 gaging stations was below normal for water year 2001, and the percent differences ranged from -28.7 to 17.9. Discharge at 36 of the 46 gaging stations was below normal for the water year 2000, and the percent differences ranged from -14.3 to -36.3. Several gaging stations that monitor heavily regulated rivers were not included in this comparison because of large artificial deficits related to regulation. The criterion of assessing gaging stations with 40 years or more of record was used in order to encompass at least one of the approximately 30-year drought cycles that New Jersey has experienced.
More than 25 heavy rainfalls occurred throughout the water year and caused flooding to some extent in the counties listed in table 2, as reported by the National Oceanic and Atmospheric Administration’s National Weather Service. Some flooding was due to heavy ice jamming in the rivers. One such event involved Green Brook. On February 6, the Union County Bomb Squad personnel evacuated nearby homes in order to detonate explosives that they planted in the ice jams on Green Brook. Melting snow also contributed to flooding on other streams in the spring.
The heavy rains that began July 12 overwhelmed many streams, especially in Burlington and Camden County. Up to 13 inches of rain fell in a 12-hour period in Tabernacle. The rain gage at the USGS gaging station, Greenwood Branch at New Lisbon, recorded 11.3 inches during July 12-13. In a 5-hour period, from 1715 hours to 2200 hours on Monday, July 12, 9.34 inches was recorded. This exceeds the predicted 100-year 24-hour rainfall frequency for Pemberton of 8.83 inches (http://www.nws.noaa.gov/ohd/hdsc/). The constant rain led to the flooding of roadways, and residents were evacuated from about 1,000 houses. According to a New Jersey Dam Safety Fact Sheet dated July 2004, 13 dams in the Burlington area failed completely, and approximately 15 other dams were damaged. Dam owners were left with the decision to remove, reconstruct, or repair their dams (http://www.state.nj.us/dep/damsafety/fact_sheet_7_12_04.pdf). Many residents in the area helped hydrographers from the U.S. Geological Survey document the high-water event, and as always, we are very grateful.
Three of the four hurricanes that hit Florida this water year made their way close enough to New Jersey to cause flooding. Hurricane Frances hit Florida September 4, then passed New Jersey on September 8, causing flooding in Bergen, Essex, Passaic, and Union Counties. Hurricane Ivan hit Florida September 15, then passed New Jersey on September 18, prompting flooding in Bergen, Hudson, Hunterdon, Mercer, Morris, Sussex, and Warren Counties. Hurricane Jeane hit Florida on September 25, then soaked the already saturated soils of New Jersey on September 25. This caused widespread flooding in Bergen, Hudson, Hunterdon, Essex, Mercer, Middlesex, Monmouth, Morris, Ocean, Passaic, Somerset, and Union Counties. The Delaware River rose to its highest level since the record flooding of August 1955 on September 18-19, 2004.
Heavy surf occurred several times in water year 2004. The December 5-6 event buckled part of the Atlantic City Boardwalk; the worst erosion was in Ocean County. The heavy surf on August 3 led to five injuries in Cape May and Atlantic City (http://www.ncdc.noaa.gov/).
The combined usable contents of 13 major water-supply reservoirs in New Jersey ranged from 90.3 to 98.9 percent of the 80.4 billion gallon capacity for the entire water year. The combined contents at the end of each month exceeded the 1961-1990 monthly averages. Precipitation was mostly above or near normal in northern New Jersey for most of the 2004 water year, which contributed to the high reservoir contents. Combined usable contents of the 13 major water-supply reservoirs was 73.5 billion gallons at the end of September 2003, which is 139 percent of the 30-year mean (normal) contents for the end of September and 91.5 percent of capacity. Combined usable contents climbed steadily from September 2003 to a maximum for the water year of 79.5 billion gallons by the end of November 2003; this is 141 percent of normal contents for the end of November and 98.9 percent of capacity. Reservoir levels remained high through the spring months, then declined slightly during the summer because of an increased demand for water supplies. Air temperatures were near or slightly above normal during the summer months. By September 30, 2004, combined usable contents totalled 76.7 billion gallons, which is 145 percent of the 30-year mean (normal) contents for the end of September and 95.4 percent of capacity (fig. 3). The term “usable contents” is used here as a measure of the total volume of water that can be removed from a reservoir without pumping and does not account for the volume of water below the bottom of the lowest outlet or pipe (sometimes referred to as dead storage).
Precipitation and Temperature
Water years 2003 and 2004 were generally wet years with above average precipitation. Before water year 2003, a trend of precipitation deficit began approximately July 1998, possibly as early as 1997. For 38 of 69 months from January 1997 to September 2002, monthly spatially weighted average-precipitation values throughout New Jersey were below the statewide long-term monthly means (1895-2002) as shown in figure 4. Precipitation data can be accessed at http://climate.rutgers.edu/stateclim/. For 32 of 51 months from July 1998 to September 2002, the monthly spatially weighted values were below the long-term monthly means. For water year 2004, the spatially weighted values for 7 of 12 months were above the long-term mean (October through December, April, and July through September were above their respective means). Calendar year 2003 was the fourth wettest year on record, and water year 2004 is the sixteenth wettest for the period of record. For water year 2004, the statewide spatially weighted average-precipitation total was 53.25 inches, which is 8.51 inches more than the long-term mean-annual precipitation from 1895 to 2002 (David Robinson, New Jersey State Climatologist, Rutgers University, oral commun., 2004). The average annual precipitation for New Jersey is approximately 45 inches. Rankings of monthly precipitation in New Jersey for water year 2004 as compared to water years 1896-2004 are listed in table 3. Monthly precipitation values are spatially weighted averages, determined using data from several dozen stations throughout the State.
The greatest daily rainfall totals for each month in water year 2004, as reported in a series of publications of the National Oceanic and Atmospheric Administration entitled Climatological Data-New Jersey, are as follows: October 27, 2.35 at Sussex (station Sussex 8 NNW); November 20, 2.40 inches at Charlotteburg Reservoir; December 11, 2.10 inches at Moorestown; January 18, 0.97 inches in Cape May; February 7, 1.89 inches in Somerville; March 19, 1.41 inches at Atlantic City Marina Station; April 13, 3.12 inches in Atlantic City Station; May 12, 2.14 inches in Plainfield; June 18, 3.08 inches at the Sussex 2 NE Station; July 13, 4.25 inches in Toms River; August 21, 3.22 inches in High Point Park; and September 18, 6.32 inches at the Belvidere Bridge Station.
Nine substantial and several smaller snowfall events occurred this year, starting as early as October 2 with a trace at High Point Park. Several trace snow events occurred in November, and several snowfalls occurred in the first half of December, with up to 17 inches on the ground in Cranford. Snowfall can remain on the ground as water in storage during days of low temperatures. As the temperature rises above freezing, the snow on the ground melts increasing the runoff into streams. For example, the 17 inches of snow cover in Cranford on December 6 melted over a period of several days. As a result of the snowmelt, the Rahway River rose above flood stage on December 11. In the second half of January, several snowfalls occurred, leaving up to a foot of snow on the ground in the northern half of the State and less than a half of a foot in the southern part of the State that stayed on the ground into February. Several light snowfalls in February kept the northern part of the State blanketed for the first 2 weeks of the month. Two snowfalls occurred in March. The first in the second week, of the month left 3 inches on the ground, and the second left up to 6 inches. Both melted quickly. The last events were on April 5 with 0.4 inches at Hammonton and on May 28 with a trace of snow at Newark International Airport.
Three National Weather Service (NWS) precipitation stations in Newark, Trenton, and Atlantic City have been selected as index sites for precipitation. During water year 2004, precipitation totals were above normal for all three index sites. Monthly totals were above or near normal for 7 of the 12 months at all three NWS index stations. The Newark station recorded 52.45 inches, which is 113 percent of the 30-year reference-period (1971-2000) mean. The Atlantic City station recorded 43.58 inches, which is 107 percent of the 30-year mean, and the Trenton station recorded 54.87 inches, which is 133 percent of the 30-year mean. Monthly precipitation at the three NWS stations, along with the 30-year mean, is shown in figure 5.
Nine of the 12 monthly mean temperatures in the 2004 water year (determined from spatially weighted average temperatures recorded throughout New Jersey) were above the long-term mean monthly average (1895- 2002). The October monthly mean was 0.3 degrees Celsius below the long-term average temperature. Monthly mean temperatures were 2.6 and 0.9 degrees Celsius above average for November and December. January averaged 3.2 degrees Celsius below average. The low temperatures of January caused streams to ice over at times. This ice cover led to ice jams and flooding on a number of streams. Monthly means from February through June ranged from 0.3 to 3.3 degrees Celsius above average. July was 0.2 degrees Celsius below average, and August and September were 0.3 and 1.8 degrees Celsius above average (fig. 6). The bookend months of the summer, May and September, were above average, and June, July, and August were very close to average (a coreless summer) (David Robinson, New Jersey State Climatologist, Rutgers University, oral commun., 2004). With the lack of long periods of extreme high temperatures, evaporation was low for water year 2004 as compared to the drought conditions that New Jersey experienced several years ago. Generally, the average temperature this water year was slightly higher than that in water year 2003. Monthly mean temperatures for the 2004 water year are listed in table 4 and are compared by rank to the historical monthly means (water years 1896-2004). May was the warmest month on record. Temperature data can be accessed at http://climate.rutgers.edu/stateclim/.