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Precipitation in the upper Delaware River basin during the 1990 River Master report year ranged from 29 percent of the long-term average during December to 187 percent during August (See table 1). Total precipitation during the year was 1.48 inches above average. Precipitation during the December to May period, when reservoirs typically refill, was slightly below average. However, the wet conditions during January and May filled the reservoirs and helped to keep flows above median for most of the year. On December 1, 1989, when this report year began, combined storage in the New York City reservoirs in the upper Delaware River basin was 238 billion gallons (Bgal), 88 percent of the combined storage capacity. Median storage on December 1, based on 22 years of data, is 158 Bgal. During the December through May period, storage in the New York City reservoirs usually increases in response to lower demand for water and to higher base flows in the streams in the basin. During the 1990 report year, storage began to decline in early December, in response to the very low precipitation and declined steadily until mid-January. However, in response to increased precipitation and warmer temperatures during the last ten days of January, the storage increased rapidly. Cannonsville Reservoir filled to capacity and began spilling by the end of [January and the combined storage continued to increase throughout February reaching 99 percent of capacity by month end. The reservoirs reached a maximum of 276.271 Bgal, combined storage for the report year on May 18, 1990 when all three reservoirs were spilling. On June 1, 1990, the start of the water-operations year, storage was 271.027 Bgal and Cannonsville Reservoir was spilling. Throughout the year, diversions to supjply water for New York City and releases designed to maintain the flow of thje Delaware River at Montague were made as directed by this office. Diversions by New York City from the Delaware River basin reservoirs did not exceed the limit specified by the Decree. The Delaware River Master Advisory Committee met at Port Jervis, New York on May 15, 1990 to discuss hydrologic conditions in the basin and operational procedures for the 1990 release season. As River Master, I informed the committee that, on the basis of information provided by New York City, the excess quantity to be released beginning June 15 was 7.381 Bgal. This water would be released at rates designed to mairitain the Montague target flow at 100 ft^/s above the normal 1,750 ft^/s specified by the Decree. On August 8, 1990, New York State requested that the Delaware River Basin Commission (DRBC) and the Parties to the Decree consider setting aside 2,000 cfs-days of the excess-release quantity, to be used if needed, for thermal protection prior to September 30, 1990. The request was based on the extraordinary hydrologic conditions in the basin that had resulted in unusually high demands on the 6,000 cfs-day thermal-release bank. On August 15, 1990, with the unanimous approval of the Parties to the Decree, the...

Graph showing mean monthly dissolved-oxygen concentrations during July for two monitoring sites on the Delaware Estuary, 1965-98-78 9. Graph showing temporal distribution of dissolved-oxygen concentration at two monitoring sites on the Delaware Estuary, July to September 1998-79 TABLES During the 1998 River Master report year, monthly precipitation in the upper Delaware River Basin ranged from 33 percent of the long-term average during August 1998 to 191 percent of the long-term average during June 1998. Total precipitation during the report year was 1.36 inches greater than the long-term average. Precipitation during the December to May period, when reservoirs typically refill, was 4.28 inches (121 percent) greater than the 57-year average. On December 1, 1997, when the report year began, combined storage in the New York City reservoirs in the upper Delaware River Basin was 112.671 billion gallons (Bgal) or 41.6 percent of combined storage capacity. Median combined storage on December 1, computed on the basis of 30 years of record, is 172.146 Bgal. Operations on December 1, 1997 were being conducted as prescribed by the "Interstate Water Management Recommendations of the Parties to the Decree" (Delaware River Basin Commission Resolution 83-13). On January 16,1998, conditions returned to normal, and operations resumed as prescribed by the Decree. Precipitation during the first seven months of the report year was above normal in all months. Storage increased rapidly during January and continued to increase during winter until the reservoirs filled and then spilled in spring. Combined storage was at full capacity from April to mid-July, and then began the seasonal cycle of decline until the end of the report year. Precipitation remained above the long-term average through June, but precipitation was below average for the remainder of the report year.