USGS - science for a changing world

Water Science for Maryland, Delaware and the District of Columbia


Streamflow data are most commonly used for assessing water supply and to determine the risk of droughts and floods. Streamflow data are also used to calculate loads of chemical constituents, and to assess how biological communities are affected by hydrologic conditions.

The USGS streamgages chosen for the monthly water summary were selected based on the following criteria:

  • Minimum period of record is 10 years of continuous data
  • Watershed areas greater than 5 square miles
  • Streamflow is not regulated, such as by a dam or diversion, and it has relatively natural flow
  • Streamflow data reflect to weather condition
  • Most of the surrounding area and watershed are not urban

Of the 33 streamgages used in this summary, 22 have more than 60 years of data, allowing for comparison to data from the historical droughts of 2002 and the 1960s. All 33 streamgages have at least 30 years of monthly mean streamflow data.

June 2018 Streamflow

Monthly mean streamflows were in the normal range (25th-75th percentiles) at 15 percent, or 5 of 33 selected USGS streamgages. Streamflow was above normal at the remaining 28 streamgages including 2 record high June monthly mean streamflows, 18 streamgages with streamflow above the 90th percentile, and 8 streamgages with streamflow between the 76th-90th percentiles. Streamflow decreased at 25 streamgages (76 percent) and increased at 8 streamgages (24 percent) between May and June.

Click here to access the clickable streamflow map

In the hydrograph for the selected streamgages, the dark line in the 5-year hydrograph represents the monthly mean streamflow for this period, and the white band shows the normal range (25th-75th percentiles) based on the period of record. The maximum monthly mean streamflow is at the top of the blue shaded section, and the lowest monthly mean streamflow is at the bottom of the tan area. Each monthly mean streamflow is colored according to the percentile rank compared to the historical data for the month.

Monthly mean streamflow at Morgan Creek near Kennedyville in Kent County, Maryland, was 8.82 cubic feet per second (ft3/s). The normal streamflow range for June is between 5.67 ft3/s and 12.40 ft3/s. Record-keeping at this streamgage began in June 1951.

At Potomac River at Hancock, in Washington County, Maryland, the monthly mean streamflow was 14,900 ft3/s, which is a record high. The previous record high was 13,400 ft3/s in 1972. Record-keeping at this streamgage began in October 1932



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