Application of spherical-rod float image velocimetry for evaluating high flow rate in mountain rivers

Abstract

Spherical-rod float image velocimetry (SFIV) is a convenient technique combining the positive functions of a rod float velocimetry (RFV) and large-scale particle image velocimetry (LSPIV) for measuring high flow rate in mountain rivers. The SFIV is the principle that the sphere allowing little image distortion according to the orientation is used as a floating tracer for LSPIV. The drifting distances of a spherical-rod float were calculated by geometrical interpretation of spherical images recorded in an experimental open channel and mountain rivers. The depth-reflecting velocities estimated by SFIV in the rivers as in the open channel coincided approximately with the velocities by visual observation from river bank despite of the long shooting distance, weather impact, and flow complicated by topography and bed materials. The velocity coefficients obtained from the experimental channel were used to evaluate depth-averaged velocity for river discharges. The high discharges estimated by SFIV in mountain rivers distributed mostly within the range of the rating curve established by RFV. The results show that the safe and efficient SFIV is a highly applicable technique in mountain rivers with the high flow rate and complex flow. In order to practically use SFIV in mountain rivers, additional studies are required for velocity coefficients depending on the water depth and draft.