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.

April 2018 Streamflow

Monthly mean streamflows were in the normal range at 55 percent, or 18 of 33 selected USGS streamgages, although the values had to be estimated in 4 of the streams due to ice. (See the “Effects of Ice on Streamflow” section). Streamflow was above normal at the remaining 15 streamgages in Maryland, Delaware, and the District of Columbia, including 2 streamgages at record February highs, 8 streamgages above the 90th percentile, and 5 streamgages with streamflows ranging between the 76th and 90th percentiles. Streamflow increased at all 33 streamgages in February.

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 Nassawango Creek near Snow Hill in Worcester County, Maryland, was 34.1 cubic feet per second (ft3/s), which is below normal. The normal streamflow range for April is between 37.5 ft3/s and 95.4 ft3/s. Record-keeping at this streamgage began in December 1949

At the Savage River near Barton streamgage, in Garrett County, Maryland, the monthly mean streamflow was 253 ft3/s, which is above normal. The normal streamflow range for March is between 85.9 ft3/s and 148 ft3/s. Record-keeping at this streamgage began in September 1948.



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