Antietam Creek near Sharpsburg, Maryland
Why does the USGS measure Streamflow?
The mission of the USGS is to provide the Nation with reliable, impartial information to describe and understand the Earth and its resources. The USGS streamflow-gaging program provides important hydrologic information that is used to help manage the Nation's water resources.
Some specific uses of streamflow data include:
· Flood forcasting and flood management
· Safe design of highway bridges and culverts
· Setting permit requirements for wastewater discharges
· Allocation of water for for municipal, industrial, and commercial uses
· Design and operation of reservoirs
· Scientific studies of long-term changes in streamflow
· Scheduling of hydropower production
What is the history of streamflow gaging at this location?
· First streamflow measurement made in 1897.
· Stream gage constructed in July 1933
· Concrete control structure built across stream 80 feet downstream from gage in 1934 to stabilize flow for ease of measurement.
What is a streamflow-gaging station?
The USGS monitors streamflow at more than 7,200 streamflow gaging stations across the United States. At each gaging station, instruments in a gage house measure and record the stream stage (level of the water surface of the stream) on a continuous basis. The amount of streamflow is later determined from the recorded stage by using a rating chart that is based on direct measurements of streamflow at different stages.
At a streamflow-gaging station, stream stage is recorded in a stilling well located in the gage house and connected to the stream by intake pipes. A stage-sensing device, such as a float-weight system, drives a recording instrument that is regulated by a clock. At most gaging stations, stage is measured and recorded every fifteen minutes.
Where does the streamflow come from and where is it going?
Streamflow at this station accumulates from a 281-square-mile drainage area upstream from the station, originating from precipitation that falls in the watershed. After passing by this station, waster in the stream flows about 4 miles to the Potomac River and then about 180 miles to the Chesapeake Bay.
The quality of the water in the stream at this station is largely determined by the uses of the land in its watershed.
Land use in the watershed:
Rural/Agricultural: 66 percent
Forest: 24 percent
Urban/Suburban: 10 percent
What is the flow at the Antietam Creek stream gage?
Streamflow is highest in spring and lowest in early fall:
Average April streamflow: 209,000 gallons per minute
Average September streamflow: 73,000 gallons per minute
Long-term average streamflow: 126,000 gallons per minute
Lowest streamflow recorded (during a drought period): 4,200 gallons per minute on November 22, 1957
Highest streamflow recorded (during a severe thunderstorm): 5,700,000 gallons per minute on July 20, 1956 (8.7 feet above flood stage of 8 feet)