Streamflow has increased throughout the Maryland/Delaware/D.C. region, and ground-water levels at the end of September are mainly in the normal range for this time of year, according to hydrologists at the U.S. Geological Survey (USGS). Although heavy rains near the end of August had little effect on ground-water levels in Maryland and Delaware, the rain from Hurricane Floyd and the subsequent September rains have begun to reverse the downward trend in water levels in most USGS observation wells.

The September precipitation caused the total river inflow to the Chesapeake Bay to be about 30.6 bgd, which was about 149 percent of the long-term September average (20.5 bgd), and nearly 3 times the inflow into the Bay in August (19.9 bgd). Although the three main rivers entering the Bay (Susquehanna, Potomac, and James) rose under the influence of Hurricane Floyd, inflows were far below record levels because of the localized pattern of rainfall during the storm [see map at http://md.water.usgs.gov/floods/floyd/rain_noaa.gif ]. However, several rivers on the Delmarva Peninsula, where most of the rain from Floyd fell, were near or broke flow records. Therefore, effects of increased nutrient and sediment loads and changes in salinity on Bay resources are probably most significant in the tidal reaches of Maryland's Eastern Shore rivers.

In September, the average daily flow rate at the gage at the Potomac River at Little Falls was about 3.7 billion gallons per day (bgd), about 192 percent of the long-term average September flow rate (1.9 bgd). The lowest flow rate for the month was about 1.3 bgd on Sept.3, and the high was about 9.6 bgd on Sept. 10. The high did not result from rains from Hurricane Floyd, which were strongly localized.

Diversions of Potomac River water for municipal use averaged about 376 mgd in September, about 20 percent less than September of 1998, and abou
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Contact: Gary Fisher
gtfisher@usgs.gov
410-238-4259
United States Geological Survey
7-Oct-1999