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.

January 2019 Streamflow

Monthly mean streamflows were above normal at 94 percent of the streamgages in January. Streamflow was at a record January high at 2 streamgages, above the 90th percentile at 18 streamgages, between the 76th and 90th percentile at 11 streamgages, and in the normal range of 25th 75th percentile at 2 streamgages. Monthly mean streamflow increased at 7 streamgages between December and January, and decreased at 26 streamgages.

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 Chicamacomico River near Salem in Dorchester County, Maryland, was 26.2 cubic feet per second (ft3/s), which is in the normal range for January.

At Marsh Run near Grimes in Washington County, Maryland, the monthly mean streamflow was 50.7 ft3/s, which is a January record high. The previous record of 30.1 ft3/s was set in 1979. January was the third consecutive month that streamflow at this site was at a record high. Record-keeping at this streamgage began in October 1963.



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