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Summary of Annual Hydrologic Conditions - 1998

Volume 1: Surface Water

Precipitation and Reservoir Contents

Water year 1998 was a year of contrasts. The water year began and ended with below-normal precipitation and streamflow, but as a result of much greater than normal precipitation during the middle six months of the year, the yearly average for precipitation was greater than normal.

On October 27, the Delaware River Basin Commission (DRBC) issued a declaration of drought warning because of several months of below-normal precipitation. A declaration of drought warning in the Delaware River Basin is issued when the combined storage in three water-supply reservoirs in the upper part of the basin in New York falls below predetermined levels.

By January 13, above-normal precipitation, snowmelt, and water-use restrictions caused reservoir levels to increase sufficiently for the drought warning to be lifted. Precipitation during January through June was much greater than normal throughout the State, making it the third wettest January through June on record. (David Robinson, State Climatologist, Rutgers University, oral commun., 1999). During one 13-day period in May, some parts of the State received as much as 5 inches of rain. Water levels in many reservoirs reached spillway levels in April and continued to spill into June. By the end of June, weather patterns had shifted again, resulting in below-normal precipitation during July through September.

Water-year 1998 precipitation totals were above normal at the Trenton, Newark, and Atlantic City National Weather Service observer stations. The Trenton station recorded 50.7 inches of precipitation, which is 116 percent of the 30-year reference-period (1961-90) mean. The Newark station recorded 50.47 inches, which is 115 percent of the 30-year mean. The Atlantic City station recorded 46.5 inches, which is 115 percent of the 30-year mean. Figure 1 shows monthly precipitation at the three National Weather Service stations compared with the 30-year means.

Combined usable contents of the 13 major water-supply reservoirs in New Jersey were 54.5 billion gallons at the end of September 1997, which is 103 percent of the 30-year mean (normal) contents for the end of September, and 67.9 percent of capacity. Contents increased to a maximum of 80.1 billion gallons by the end of April, which is 112 percent of normal contents for the end of April, and 99.7 percent of capacity. By September 30, 1998, the contents had declined to the minimum contents for the water year, 45.7 billion gallons, which is 86.6 percent of normal contents for the end of September, and 56.8 percent of capacity (fig. 2). 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 1. Monthly precipitation at three National Weather Service locations. Figure 2. Combined usable contents of 13 major water-supply reservoirs.
Figure 1 Figure 2



The first noteworthy hydrologic event of the water year was the tidal flooding (at high tide) on November 7 that caused beach erosion in Atlantic and Ocean Counties. Several "Nor'easters" in November, December, and January brought more tidal flooding and beach erosion in Atlantic and Ocean Counties. The "Nor'easter" of February 4 packed more force than previous ones, and resulted in widespread flooding and $17 million in property damage. Governor Christine Whitman declared Monmouth, Ocean, Atlantic and Cape May Counties to be disaster areas.

Streamflow at the index station for northern New Jersey (South Branch Raritan River near High Bridge) averaged 119 ft3/s for the water year, which is 96.7 percent of the 1919-98 average. Streamflow at the index station for southern New Jersey (Great Egg Harbor River at Folsom) averaged 87.6 ft3/s, which is 102 percent of the 1926-98 average. The observed annual mean discharge of the Delaware River at Trenton was 12,810 ft3/s, which is 109 percent of the 1913-98 average. The Delaware River is highly 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 3. Annual mean discharge at each of these index gaging stations and the mean annual discharge for the period of record are shown in figure 4. Peak discharges at selected streamflow-gaging stations in the State are listed in table 1 (view table in pdf format).

Figure 3. Monthly discharge at index gaging stations. Figure 4. Annual mean discharge at index gageing stations. Table 1. Instantaneous peak discharge
for water year 1998 and maximum
instantaneous peak discharge for
period of record prior to the 1998
water year at selected sites
in New Jersey
Figure 3 Figure 4 Table 1


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