RESPONSE OF SURFACE VELOCITY COEFFICIENT TO LONGITUDINAL BATHYMETRY VARIATION

The surface velocity coefficient is the value that converts the surface velocity into the depth-averaged velocity when observing the discharge, and 0.85 is treated as the standard value in Japan. In recent years, surface velocity measurement by STIV is widely used, but only surface flow information can be obtained. Therefore, it is important to properly determine the coefficient when estimating the discharge. In this paper, we focused on the situation where the water depth gradually changes due to the formation of sandbars. We conducted flume experiments to examine the response characteristics of the surface velocity and the surface velocity coefficient caused by changes in the riverbed slope. As a result, it was shown that the change of the correction coefficient is not symmetrical with respect to the riverbed topography, and that the coefficient decreases sharply on the downstream side of the sandbar because the influence of negative acceleration is large. The above characteristics are verified through numerical simulations as well.