Abstract
The discharge of the overflow at a dam is currently determined by applying an empirical equation estimated on ideal system to water level at the dam. However the real overflow on large scale has many uncertain factors and thus the estimated discharge has large errors, which may be order of several ten percent. Until now, we have studied an overflow measurement by using ultrasonic velocity profiler (UVP) to realize more accurate measurement of the discharge (Kashiwaguma, 2003). Cross-sectional velocity distribution over the weir setting in an open channel was measured by UVP and discharge calculated from velocity distribution was compared with discharge determined from the empirical equation. That system has slightly error because of rough detecting the position of free surface on measurement line. To reduce error in the measurement of the discharge, we must acquire the position exactly. In this study, we attempted to utilize the amplitude information of US echo which has not been used to calculate the velocity profile in conventional UVP. The velocity profile was measured in the vertical direction on the condition accompanying free surface in an open channel. The time evolution of the free surface displacement was measured by using the amplitude information of reflected ultrasound at the surface. The measured position was compared with an alternative measurement method based on the position meter fixed on the measurement line of UVP and then the accuracy of the present method was verified.
