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Summary of Annual Hydrologic Conditions - 2003

Volume 1: Surface Water


Three gaging stations, located in north, south, and central New Jersey, are considered index stations for statewide streamflow conditions. Streamflow at the index station in northern New Jersey (South Branch Raritan River near High Bridge) averaged 145 ft3/s for the water year, which is 119 percent of the 1919-2003 average. Peak flow for the water year was 1,350 ft3/s on September 23; the recurrence interval is less than 2 years. The lowest daily mean flow was 16 ft3/s on October 9, which is about the 99-percent flow exceedance.

Streamflow at the index station in southern New Jersey (Great Egg Harbor River at Folsom) averaged 101 ft3/s, which is 119 percent of the 1926-2003 average. Peak flow for the water year was 381 ft3/s on February 25; the recurrence interval is from 2 to 5 years. The lowest daily mean flow was 20 ft3/s on October 7, which is about the 99-percent flow exceedance.

The observed annual mean discharge for the Delaware River at Trenton was 17,110 ft3/s, which is 147 percent of the
1913-2003 average. Peak flow for the water year was 83,100 ft3/s on March 22 and the recurrence interval is from 2 to 5 years. The lowest daily mean flow was 3,130 ft3/s on October 5, which is about the 90-percent flow exceedance. The Delaware River is significantly regulated by reservoirs and diversions. Monthly mean discharge at each of these index gaging stations during the current water year and the long-term normal monthly discharge are shown in figure 1. Annual mean discharge at each of these index gaging stations and the mean annual discharge for the period of record are shown in figure 2.

Figure 1. Monthly mean discharge at index gaging stations. Figure 2. Annual mean discharge at index gaging stations.
Figure 1 Figure 2

Annual mean discharges for water year 2003 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 2003. 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.

Table 1. Annual mean discharges for water year 2003 and mean annual discharge for the period of record at selected continuous
gaging stations with 40 years or more of records
[ft3/s, cubic feet per second; mi2, square miles]

Table 1


Minor riverine and coastal flooding occurred several times throughout the water year, most notably in September as a
result of Tropical Storm Isabel. Two major floods occurred in the last 5 years -- the Sparta Flood caused by a series of heavy, localized thunderstorms in August 2000 and the flooding of historical proportions that occurred in many areas of the State when Tropical Storm Floyd combined with a storm system from the west in September 1999.


Reservoir Contents

Reservoir levels that reached near record lows at times during water year 2002 increased this water year as a result of above normal precipitation for most of water year 2003. Combined usable contents of 13 major water-supply reservoirs in New Jersey were 47.2 billion gallons at the end of September 2002, which is 89.4 percent of the 30-year mean (normal) contents for the end of September and 58.7 percent of capacity. Combined usable contents climbed steadily from September 2002 to a maximum for the water year of 80.2 billion gallons by the end of March 2003, which is 115 percent of normal contents for the end of March and 99.7 percent of capacity. Reservoir levels remained high until the end of June, then experienced a slow, but normal, decline during the summer because of an increased demand for water supplies. Above normal air temperatures during the summer months can increase evaporation rates for the reservoirs. By September 30, 2003, combined usable contents totalled 73.5 billion gallons, which is 139 percent of the 30-year mean (normal) contents for the end of September and 91.5 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).

Figure 3. Combined usable contents of 13 major water-supply reservoirs.
Figure 3


Precipitation and Temperature

Prior to this water year, the State of New Jersey had been in a state of water emergency, declared on March 4, 2002, by Governor James E. McGreevey (Executive Order No. 11), after many months of precipitation deficits (including February 2002, the driest February on record). Water year 2003 began with 3 months of above normal precipitation from October to December 2002, making it the sixth wettest fall on record (compared to 108 years of record). This prompted Governor McGreevey to lift the statewide drought emergency on January 8, 2003. On March 26, 2003, the drought warning was lifted in Coastal South and Southwest Drought Regions, bringing the entire State to “Normal” status. More information on the New Jersey drought is available at

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 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 2003, the spatially weighted values for 8 of 12 months were above the long-term mean (October through December, February, March, June, August, and September were above their respective means). Calendar year 2003 is the fifth wettest for the period of record. For water year 2003, the statewide spatially weighted average-precipitation total was 59.09 inches, which is 14.35 inches more than the long-term meanannual 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.

Figure 4. Monthly precipitation for water years 1997-2003 in New Jersey and long-term mean-monthly precipitation for period 1895-2002.
(Long-term mean-monthly and monthly precipitation are spatially weighted averages for several dozen stations throughout the State.)
Figure 4

The greatest daily rainfall totals for each month in water year 2003 as reported by the National Weather Service (NWS) are as follows: October 11, 3.41 inches in High Point Park; November 17, 2.60 inches in Toms River; December 26, 3.00 inches in Long Branch Oak Hurst; January 4, 2.25 inches in Toms River; February 17, 3.04 inches in Plainfield; March 30, 2.16 inches in Belleplain State Forest; April 8, 1.21 inches in Long Branch Oakhurst; May 26, 1.62 inches in Cranford; June 5, 3.79 inches in Harrison; July 22, 2.20 inches in Flemington; August 6, 2.82 inches in Canoe Brook; and September 4, 3.76 inches in Indian Mills.

Thirteen snowfall events occurred this year, starting as early as October 30; the last event was April 7. Most notable was the February 17 snowstorm that left 15 to 20 or more inches covering most of New Jersey. A weak El Nino subsided, and the Pacific Ocean temperatures returned to normal in March. These circumstances can contribute to increased rain and snowfall. The April 7 snowfall left 5 to 8 inches in central and north central New Jersey and 1 to 3 inches in the northern and southern areas. Tropical Storm Isabel passed south of New Jersey on September 19, but associated rainfall caused some flooding.

Three NWS precipitation stations in Newark, Trenton, and Atlantic City have been selected as index sites for precipitation. During water year 2003, precipitation totals were above normal for all three index sites. Monthly totals were above or near normal for 8 of the 12 months at all three NWS index stations. The Newark station recorded 58.55 inches, which is 127 percent of the 30-year reference-period (1971-2000) mean. The Atlantic City station recorded 50.04 inches, which is 123 percent of the 30-year mean, and the Trenton station recorded 49.14 inches, which is 119 percent of the 30-year mean. Monthly precipitation at the three NWS stations, along with the 30-year mean, is shown in figure 5.

Figure 5. Monthly precipitation at three National Weather Service stations.
Figure 5

Three tornados were reported in New Jersey on September 23. These were classified as F1 Category Tornados on the
Fujita Tornado Scale (moderate tornado with 73-112 mph wind speed, causes moderate damage). One of the tornados damaged at least three houses in Hunterdon County. A tornado in Florence uprooted approximately 100 trees, and the other tornado damaged several commercial establishments in Mercer County.

Eight of the 12 monthly mean temperatures in the 2003 water year (determined from spatially weighted average temperatures recorded throughout New Jersey) were below or equal to the long-term mean monthly average (1895-2002). The October monthly mean equaled the long-term average temperature. Monthly mean temperatures ranged from 0.3 to 2.3 degrees Celsius below average for November through February. March averaged 0.6 degrees Celsius above average. Monthly means from April through June were as much as 1.8 degrees Celsius below average. From July through September, temperatures were above average (fig. 6). Generally, the average temperature this water year was lower than in water year 2002. Temperature data can be accessed at

Figure 6. Water year 2004 monthly mean air temperatures and long-term mean-monthly air temperatures for New Jersey.
figure 6


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