How Does Stream Flow Change over Time?
ES1301  Measuring Stream Flow

The amount of water flowing in a river is called the discharge. Specifically, discharge is the volume of water that flows past a point during a specific time. Discharge is usually reported as the number of cubic feet of water passing a point each second, abbreviated as cfs (cubic feet per second).

Across the country, discharge is measured in many ways. On some rivers, devices called stilling wells are installed. The height of water in the well is proportional to the discharge.

Discharge can also be measured using weirs, small "walls" built across rivers to force the flow through a V-notch at the top. The height of the water level in the notch indicates the amount of discharge.

Current meters can be used to measure river velocity. The measured velocity must be multiplied by the river's cross section to calculate discharge.

USGS
Stilling well used to measure stream flow.
USGS
Schematic of a stilling well and shelter at a stream-gauging station.
USDA, Forest Service
The height of water passing through the notch in the weir can be used to measure discharge.
USGS
Current meter and weight suspended from a bridge crane.

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