In a typical year, highest streamflows occur during the winter months, decreasing through the spring and summer, with lowest streamflows occurring during the fall months.
During the winter of 1998, above average precipitation recharged the ground-water system, which in turn, maintained streamflows in the above normal range of flows. Even though there was below average precipitation during the spring and summer of 1998, streamflows did not fall below normal until September of that year because of the high ground-water storage. With continued dry conditions in the fall, ground-water storage became depleted, and streamflows continued to decline to levels near those observed in past droughts. Streamflows remained in the below normal range during the winter of 1999 because precipitation was insufficient to fully recharge the ground-water system. During base-flow conditions (non-storm runoff), streams had about one-third of the flow during the winter of 1999 than they had during the winter of 1998. The already depleted ground-water storage conditions combined with less than normal precipitation during the past three months has resulted in continued low streamflows. June streamflows are already at or near typical annual low flow values, and streamflows are expected to continue to decline through the summer.
There have been four major Statewide droughts since the early 1900's. The drought of 1930-32 was one of the most severe droughts recorded in the State. Recurrence intervals ranged from 30 years to greater than 80 years. The droughts of 1938-42 and 1962-71 were less severe; however, the cumulative streamflow deficit for the 1962-71 drought was the greatest of the four droughts because of the duration of this drought. The drought of 1980-82 was the least severe and had the shortest duration. Recurrence intervals in the 1980-82 drought ranged from 15 years across most of the State to greater than 80 years in the James River Basin.
U.S. Department of Interior, U.S. Geological Survey
Last modified: 03/12/02 07:00:36 AM