All surveys begin with a reference point. Any stream gager knows how cableways swing, sag, and sway, especially when the cablecar is attached to a lead weight swimming in flood water. Although the movement is tolerable for approximate depth measurements and average velocity, the movement biases readings from accurate sensors. The shore-mounted aluminum boom pivots in vertical and horizontal axes. Velocity meters and sonar transducers are mounted at the bottom of the vertical-support pipe.
Relative elevation is determined by level sight to the staff plate on the boom.
This sketch describes velocity meters and sonar transducers mounted on the vertical-support pipe. Taken from a video source, this image shows three velocity meters mounted on a fiberglas frame and attached to a steel vertical-support pipe. A sonar transducer is connected to the bottom of the pipe. Two of the black boxes for velocity measurements are shown inside a gage house. The meters are connected to the boxes by cable longer than 100 feet.