Abstract
It is important to measure the flow speed and flow rate at the flood. To develop the measurement system of flow speed for the flood, we measured quantitatively the long-term characteristics of sound propagation in the river. In this paper, we present the preliminary results of long-term measurement that have performed at Uono River. We found the variation of the time of flight with several minutes period and obtained the quantitative characteristics of the defect of sound propagation at the flood.
