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.

March 2019 Streamflow

Monthly mean streamflows were at or above normal at 94 percent of the streamgages in March. Streamflow was above the 90th percentile at 8 streamgages, between the 76th and 90th percentiles at 13 streamgages, in the normal range (25th 75th percentiles) at 10 streamgages, and below normal at 2 streamgages in western Maryland. Monthly mean streamflow increased at 21 streamgages between February and March, and decreased at 12 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 Deer Creek at Rocks, in Harford County, Maryland, was 379 cubic feet per second (ft3/s), which is in the above normal range for March. Streamflow has been above normal for the previous 6 consecutive months. Record-keeping at this streamgage began in October 1926.

At Bear Creek in Garrett County, Maryland, the monthly mean streamflow was 124 ft3/s, decreasing from above normal for the previous 6 months to below normal in March. Record-keeping at this streamgage began in October 1964.



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