The Potomac River, low and sluggish from more than a month without significant rainfall, has dropped to one of its lowest spring levels on record, presaging what some water officials fear may be a return to the drought cycle of the 1980s.
Despite rain today expected to average around an inch in some western parts of the Potomac River basin, the river is expected to remain at its current level or continue dropping.
"An inch (in the basin) hardly shows up at all by the time time it gets down here," said Leo Harrison, who forecasts river flows for the National Weather Service. "We're in a drought situation . . . it doesn't look too favorable."
Harrison and other hydrologists emphasize that it is still too soon to tell what the current drought will mean for the rest of the year. They point out that a two-inch rainfall over the basin could break the drought and return the Washington area's water table to something approaching normal. Other years, which have started out this dry or drier, have been transformed by a rainy June.
But Harrison is not optimistic.
"This system coming in (today) is not that big, and after that it looks like we'll return to a fair weather pattern for the next 30 to 60 days, he said. "We go through a droguht cycle like this about every 10 or 12 years. It's been 11 years since the last one. People seem to forget."
The five-year drought in the early 1960s produced the Potomac's slowest rate of water flow on record: 388 million gallons on Sept. 10, 1966. Normal daily flow in September is about 2 billion gallons.
What worries local authorities is that Washington area jurisdictions collectively have drawn more than 388 million gallons from the river on each of a few hot days every summer since 1966 - including four days last June. So far the periods of lowest flow and highest use have not coincided, but most people believe it is only a matter of time.
The river's low level in September, 1966, however, was the cumulative effect of five years of drought - a drought that broke five days later with heavy rains. Actually the total 12-month flow during the year of 1930, was lower than during 1966 although no single day produced a flow as low as 388 million gallons.
On June 1, 1930, the river flowed past Washington at the rate of 1.8 billion gallons a day. Yesterday the rate of flow dipped to 1.7 billion gallons. On June 1, 1966, the fklow was 3.8 billion gallons.
The Potomac supplies the drinking water for the District of Columbia. Arlington County and Falls Church, and about 80 per cent of the homes in Montgomery and Prince George's counties. Alexandria, Fairfax County and most of Prince William County draw their water from the Occoquan Reservoir, which forms parts of Fairfax County's southern border.
The Potomac River is only one indicator of the drought in the Washington area. Another is the water table, which has been falling steadly since April.
Though only three of the last 15 months have been normal or wetter than normal, Harrison said, two of those were March and April. The rains from those months are still in the ground, providing a cushion of mositure for future needs.
But Harrison said some shallow wells in Prince William County already are going dry and int he Shenandoah Valley, driest area of the Potomac River Basin, some crops have taken almost a month to germinate in the dry soil.
Wayne Solley, hydrologist for the U.S. Geological Survey in Towson, Md., said a single month such as May is too short a time on which to base a trend of seriously declining river levels during the next 30 days. ogists will be closely watching the rivere levels during the next 30 days.
"A lot depends on June," he said. "If June is very dry, then streamflows may decline to a rate where the ratio of water withdrawn to the water flowing in the river would be uncomfortably narrow."