Abstract
As for the flow rate measurement in a conventional open channel, there is a problem to change the instruction value of flow rate. Highly accurate flow rate was studied by measuring the instantaneous velocity distribution of the flow field with ultrasonic velocity profiler (UVP) and integrating the cross section. The velocity distribution was able to be obtained by measuring at the direction of the crossing and depth, to understand the flow field in three dimensions, and to have constructed the open channel monitor system that was able to make a change with the lapse of time of the flow field visible.