The meter consists of cups that are rotated by the action of flowing water. The speed of the rotation depends on the velocity of the water passing by the cups. A technician counts the number of revolutions in a given time interval and determines the velocity at the location of the meter. The stream is divided into segments and average velocity and depth of the stream are measured at each segment. The discharge in each of the segments are then summed to obtain the total stream discharge.
Technicians obtain measurements several ways depending on the size and depth of the river.
They will wade across small streams, use suspended cableway cars, or stand on bridges to measure streamflow in large rivers. Technicians are measuring discharge of the river by making observations of width, depth, and velocity using a current meter. Insert shows a current meter attached to a weight. This weighted current meter is lowered into the river from a bridge or cable car such as pictured in the cover photo. The rating curve for a specific stream location is developed by making successive discharge measurements in order to define and maintain a stage-discharge relation.