After six consecutive years of above-average flows, the Potomac River returned to a near-normal level in 1979, the U.S. Geological Survey reported yesterday.
The average daily flow during the year was about 7.7 billion gallons of water, just slightly above the annual normal rate of 7.0 billion gallons a day.
A USGS spokesman said the flow has been above normal every year since 1970, contrasting with the dry years of the late 1960s. The average flow peaked in 1972 at 13.7 billion gallons a day, due largely to flood runoff from Tropical Storm Agnes in June that year.
Monthly rates of flow in 1979 were above average in October, November and December. The December flow averaged about 6.8 billion gallons per day, which is about 30 per cent above the normal flow for that month.
The highest single daily rate of 1979 was 112 billion gallons of water on Oct. 11, due to flood runoff from the rains of Oct. 8 and 9, USGS reported. The low was reached Sept. 8, when a flow of 1 billion gallons was recorded.
The all-time daily high was recorded on March 9, 1936, when 275 billion gallons of water was monitored, and the record low was 388 million gallons on Sept. 10, 1966. The Geological Survey has kept records since 1930.
USGS hydrologists said ground water levels throughout the Potomac basin were above normal in 1976. At the end of the year, the level at a local observation well stood at 11.9 feet below the land surface, 0.7 feet above average.
The ground level, which has been recorded since 1955, reached a record high for the month of October when it rose to 9.9 feet below the land surface. Ground levels in the metropolitan area have been above normal for 18 consecutive months.