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Hydrologic Conditions Annual Report 2002


The drought that began during the summer of 2001 continued unrelenting into 2002. As of January 1, the Delaware Basin remained under the drought emergency declared by the Delaware River Basin Commission (DRBC) on December 18, 2001, and the majority of the counties within the basin were under state-declared drought actions. With less than a 33 percent chance that the New York City (NYC) Delaware reservoirs would refill by June 1, a drought warning was issued by the NYC Department of Environmental Protection on January 28.

Below-normal precipitation persisted throughout January and into February. February was a particularly dry month, setting records in Philadelphia and Allentown. Much needed relief arrived in early spring when normal- to above-normal rainfall patterns returned to the basin. Stream levels rose, reservoirs made gains in storage, and ground water in many wells began a seasonal, upward trend. By April 1, a combination of rainfall and snowmelt caused the NYC Delaware reservoirs to rise above the drought threshold for the first time since November 2001, and by May 26 the storage in the reservoirs had remained at least 15 billion gallons (bg) above the drought watch threshold for five consecutive days. As a result of this improved storage, the basin returned to the DRBC's normal operating plan, although the commission's drought emergency continued to remain in effect. With the return to normal operations, normal flow objectives at Montague and Trenton, New Jersey resumed, as did normal out-of-basin diversions to New York City and New Jersey.

By July 8, the NYC Delaware reservoir storage had remained more than 40 billion gallons (bg) above the drought watch threshold for more than 30 consecutive days. Although the DRBC Water Code would have allowed the commissioners to terminate the drought emergency under these circumstances, they unanimously decided at their July 17 meeting to continue the drought emergency status for at least another thirty days. A dry weather pattern persisted during this time, making a decision to lift the emergency questionable. On August 6 via a telephone conference, the commissioners once again unanimously agreed to continue the drought emergency until October 16, with the option to terminate it before this date if hydrologic conditions improved sufficiently.

The dry weather pattern broke by early autumn and ample rainfall returned to the basin by the end of September. Although the drought indicators were showing signs of improvement, another period of dry weather could have easily wiped out any gains. With this in mind, the commissioners unanimously agreed at their October 16 meeting to continue the drought emergency until November 25, once again with the option to terminate the emergency prior to this date.

Drought indicators across the basin continued to show signs of improvement throughout the remainder of autumn. The commissioners approved Resolution 2002-31 at their November 25 meeting terminating the drought emergency in the Delaware River Basin. Ample rainfall continued through the end of the year, prompting the lifting of various state-declared drought actions as well (see the attached document, Chronology of Drought in the Delaware River Basin, for a timeline of drought declarations and actions).


The majority of the counties within the Delaware River Basin reported normal- to above-normal precipitation by the end of 2002. Year-end precipitation surpluses ranged from 0.10 inches to as much as 10.10 inches. Only 11 basin counties reported annual deficits. These deficits ranged from 0.10 inches to 2.80 inches, a vast improvement over 2001, a year that ended with every county in the basin reporting a deficit ranging from one inch to nearly 13.5 inches. See the attached map in Figure 1: 2002 Annual Precipitation Departures in the Delaware River Basin for a depiction of average precipitation departures by county.

The observed precipitation above Montague, New Jersey for 2002 was 46.56 inches, or 3.30 inches above normal. Annual observed precipitation above Trenton, New Jersey was 47.05 inches, or 2.82 inches above normal. See the attached Table 1: Precipitation at Selected Stations in the Delaware River Basin for additional monthly precipitation data for selected basin locations.


Streamflows throughout much of the Delaware River Basin averaged below normal through April, but improved by May when frequent spring rains caused streams to rise to above-normal levels. By the end of May, average streamflows for the Delaware River at Montague and Trenton, New Jersey were 53 percent and 64 percent above normal, respectively. Above-normal streamflows continued into June, with the Delaware River at Montague recording an average streamflow of more than double the normal flow for the month. Observed monthly streamflows on both the Lehigh and Schuylkill Rivers also averaged above normal May through June.

Streamflows declined during the summer months and averaged below normal through early autumn. However, remnants of Hurricane Isidore in late-September as well as two- to five-inches of rain in mid-October provided relief. This pattern of frequent and plentiful rainfall boosted streamflow averages to more than double their normal flow for October. Delaware River flows at Montague and Trenton averaged 133 percent and 150 percent above normal, respectively. Similarly, flows for the Lehigh River at Bethlehem averaged 105 percent above normal and flows for the Schuylkill River at Philadelphia averaged 143 percent above normal. Above-normal precipitation during the last two months of the year, including a northeaster that dropped up to three inches of rain over most of the basin in mid-November, kept rivers and streams flowing at above-normal levels through the close of 2002. See the attached Table 2: Streamflow in the Delaware River Basin 2002 for average monthly streamflows at selected stations. Also, please refer to Figure 2: Delaware River at Montague, NJ 2002 and Figure 3: Delaware River at Trenton, NJ 2002 for annual hydrographs of these two Delaware River stations.

Reservoir Storage

Lower Basin

F.E. Walter Reservoir, a United States Army Corps of Engineers (USACOE) flood control project located on the Lehigh River, was used to provide temporary water storage for the drought beginning on February 1, 2002. From mid-July through mid-August, the USACOE made releases to the Lehigh to improve the quality of recreational activities, such as boating, swimming, and fishing. The DRBC also made use of F.E. Walter's temporary storage, using the water for releases to augment streamflows at Trenton, New Jersey. During August and September, DRBC requested releases totaling 1.034 billion gallons (bg) from the reservoir’s temporary water storage. When hydrologic conditions improved from late-September through early-November, the USACOE began to lower F.E. Walter Reservoir to its normal elevation of 1,300 feet. Storage was gradually released from the reservoir until the normal elevation was reached on December 19, 2002.

Both the Beltzville Reservoir (located on Pohopoco Creek, a tributary of the Lehigh River) and the Blue Marsh Reservoir (located on Tulpehocken Creek, a tributary of the Schuylkill River) maintained normal storage throughout 2002. No releases were directed from Beltzville Reservoir during the year. The DRBC made directed releases from Blue Marsh Reservoir totaling only 0.614 bg for a short period between August and September. Please refer to Figure 4: Blue Marsh Reservoir Elevation, Figure 5: Beltzville Reservoir Elevation, and Figure 6: F.E. Walter Reservoir Elevation to view the 2002 storage elevations for these lower basin reservoirs.

In addition to the available water storage in F.E. Walter, Beltzville, and Blue Marsh reservoirs, releases were made from Merrill Creek Reservoir (located in Phillipsburg, New Jersey) in January 2002 to augment flows at Trenton and to replace evaporative losses caused by power generation. Such releases are required by Merrill Creek's operating plan whenever the Delaware Basin is under drought operations based on water supply storage in the NYC Delaware reservoirs. Merrill Creek’s last 2002 release was made January 24, for a total annual release of 0.42 bg.

Upper Basin

The NYC reservoirs in the upper Delaware River Basin began the year with water supply storage far below normal. As of January 1, the reservoirs had a combined storage of 69.785 bg, which was nearly 120 bg below normal. Although the supply was far below normal for the date, storage had actually improved from two weeks earlier when the three NYC Delaware reservoirs held only 63.348 bg on December 15, 2001, a record-low since Cannonsville Reservoir came on-line in the 1960s.

In order to meet the Montague, New Jersey flow objective while conserving water storage in the NYC Delaware reservoir system, power releases totaling 0.51 bg were made from Lake Wallenpaupack in late-January under the drought emergency provisions of the DRBC Water Code. Lake Wallenpaupack is a power generation impoundment owned by PPL Generation, LLC and is located on Wallenpaupack Creek, a tributary of the Lackawaxen River, near Hawley, Pa.

Reservoir storage continued to increase during early 2002. Record breaking warm weather in late-January caused the majority of the snowpack (approximately 37 bg of water equivalent by late-January) to melt. Runoff from the snow melt boosted reservoir storage to over 106 bg by the end of February. Despite this promising gain in storage, the NYC Delaware reservoirs failed to refill to capacity during 2002. On May 1, the normal date for refill based on historical data, the combined storage in the three NYC reservoirs was only 169.405 bg, which was 101.877 bg below the long-term median storage for the date. By June 1, the NYC reservoirs had continued to gain storage, but were still nearly 50 bg below capacity. On June 24, the NYC reservoirs reached an annual peak of 243.584 bg (89.9 percent of usable capacity), which was more than 27 bg shy of refill.

On July 4, the Delaware River Master began making releases from the NYC Delaware reservoirs to augment streamflows at Montague. Directed releases continued on an almost daily basis until October 13. The River Master directed a total of 47.252 bg of releases during this four-month timeframe.

During the period from late-September through mid-October, heavy rainfall resulted in significant storage gains in the three NYC Delaware reservoirs. By late-October, storage was above the long-term median storage for the first time since May 2001. Storage continued to increase through the end of the year. As of December 31, the combined storage in the NYC Delaware reservoirs was 223.635 bg, which was nearly 35 bg above the long-term median storage for the date. For a graphical presentation of NYC reservoir storage levels for 2002, please refer to Figure 7: New York City Delaware River Basin Storage 2002.

Ground Water

Many wells throughout the basin began the year with levels significantly below normal. As of January 2002, the average ground water levels of eight observation wells in the Pennsylvania portion of the basin were below the normal average, with half of the observation wells registering record-low levels. Water levels in three observation wells in the coastal plain region of Delaware (New Castle County and Kent County) and New Jersey (Cumberland County) also remained far below normal levels, with the Cumberland County well registering record-low levels.

By May, the average ground water level in the eight Pennsylvania observation wells still remained below the normal average, although an upward trend could be observed. Average ground water levels aside, a look at each individual well’s performance told a slightly different story and revealed regional differences. Three of the observation wells in the northeastern portion of Pennsylvania fully recovered to normal levels by the end of May, while wells in three other counties in the state remained in drought emergency status and were registering record-low levels for the month. The other two observation wells were showing a significant recovery, but remained below the normal range. As for the coastal plain wells in New Jersey and Delaware, all three displayed an upward trend as of the end of May, but were still recording record-low levels.

By summer, many wells in the basin had begun their normal seasonal downward trend as evapo-transpiration rates increased and limited recharge occurred. During the summer months, the ground water in the eight Pennsylvania observation wells remained below the normal average levels, as did the ground water levels in the coastal plain wells.

Wet weather from September through November provided much-needed recharge for wells throughout the basin. Ground water levels within the Pennsylvania observation wells climbed steadily from early autumn through the end of the year. Ground water levels within the coastal plain wells in Kent County and Cumberland County also climbed steadily upward. The coastal plain well in New Castle County was slower to react and remained stationary throughout November before starting to show signs of recovery. Despite these recoveries, the Pennsylvania observation wells and the coastal plain wells in Cumberland County and New Castle County remained below the normal average level by the close of 2002. Only the coastal plain well in Kent County managed to recover to an above-average level by the end of December. See the attached Figure 8: USGS Network Wells-Pennsylvania, Figure 9: USGS Well-New Castle Co., Delaware, Figure 10: USGS Well-Kent Co., Delaware, and Figure 11: USGS Well-Cumberland Co., New Jersey for graphical presentations of ground water levels throughout 2002.


The seven-day average of the 250 parts-per-million isochlor (salt front) was located upstream of its normal location through mid-May 2002. Precipitation during May raised streamflows enough to cause the salt front to retreat to river mile 59 on the Delaware River by May 21. This was to be the salt front's furthest downstream location during 2002. Below-normal streamflows during July and August took their toll and by early-August, the salt front advanced to above its normal location for the month. By August 31, the salt front was located just above the mouth of Crum Creek at river mile 85.

Below-normal streamflows persisted throughout most of September, resulting in increased chloride concentrations and an advancing salt front. By late-September, the salt front had advanced to its furthest upstream location for the year, river mile 89. This location is near Philadelphia International Airport and is ten miles upstream of September's normal location (river mile 79).

The salt front retreated rapidly downstream with October's above-average rainfall. During the month of October alone, the salt front retreated twenty miles from river mile 88 on October 1 to river mile 68 on October 31, 13 miles below the month's normal location. Continuing above-average precipitation during November resulted in the salt front retreating even further down the Delaware River to river mile 63. The year closed with the salt front at river mile 65, four miles below the Delaware Memorial Bridge and nine miles below the normal location for the month. See the attached Figure 12: Location of the 7-Day Average of the 250-PPM Isochlor for an overview of salt front locations along the Delaware River in 2002.

This report was prepared by the DRBC Operations Branch.