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Missouri River Streamflow-Gaging Station

Bismarck, North Dakota


How Does the USGS Collect Streamflow Data?

Constructing the Bismarck Gage House1.  A Gage Site is Established

The U.S. Geological Survey selects a suitable site along a river or stream and constructs a gage house to hold equipment that measures and records the height of the water surface (gage height or stage).  The gage house also can hold equipment that measures water-quality parameters, such as temperature, pH, dissolved oxygen, and dissolved chemicals, and weather conditions, such as air temperature, precipitation, and wind speed.  The Bismarck gage house contains a U.S. Army Corps of Engineers camera that displays pictures of the Missouri River on the Internet at https://webcam.crrel.usace.army.mil/bismarck/.

2. The Water Level is Measured and Recorded

The gage height (or stage) of a river most commonly is measured through the use of a stilling well, a bubble system, or a wire-weight gage.

Schematic of a stilling well and shelter at a stream-gaging stationA stilling well (pictured at right) is used when a gage house can be built immediately adjacent to a river.  The well is connected to the stream with pipes so that when the water level in the stream changes, the water level in the well also changes.  A float in the well is connected to a recorder or data-collection platform.

The Bismarck gage house uses a stilling well to measure gage height.



Gage House and Bubble SystemThe bubble system (pictured at right) can be used when construction of a well is not feasible.  The bubble system requires a long open-ended pipe that extends from the gage house to the river.  One end of the pipe is fixed securely below the water surface, and pressurized gas (usually nitrogen or air) is forced through the pipe from inside the gage house and out a submerged opening called an orifice.  The pressure in the pipe is determined by how deep the water is over the orifice.  A change in the water level of the river produces a corresponding change in the pressure in the pipe.  The change in pressure is converted to an electronic signal by a transducer inside the gage house.  Data from the transducer then is fed to a recorder, or data-collection platform, which records the corresponding gage height.



An outside reference gage, typically a vertical graduated ruler called a staff gage, is read periodically to verify that the recorded gage heights from the stilling well or bubble system are the same as the water levels in the stream.


Bismarck wire-weight gageA wire-weight gage (pictured at right) consists of a drum wound with a single layer of stainless-steel cable attached to a bronze weight, a graduated disc, and a counter, all within a cast-aluminum box.  The weight may be lowered to the water surface using a hand crank.  When the bottom of the weight is at the water surface, the gage height is indicated by the combined readings of the counter and the graduated disc.  The wire-weight gage commonly is mounted on a bridge handrail, parapet wall, or pier for use as an outside gage.



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Page Last Modified: Wednesday, 27-Feb-2008 17:07:27 EST
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