2025 Volume 81 Issue 15 Article ID: 24-15002
Water level and flow rate are the basic hydraulic quantities that represent flood flows, and their observation is important. Recently, methods for estimating water surface velocities using image analysis such as PIV have been developed and put into practical use. The estimation of the flow regime during a flood event has been challenging due to the difficulty in measuring three-dimensional internal flow velocity profiles and bed levels. In this study, the water surface fluctuations measured at two points in a straight channel were discussed to estimate the surface stream-wise velocity and water depth, with a focus on the difference in the celerity between forward and backward gravity wave with various wave lengths. This was done as a first step to estimate the internal flow structures from the surface flow images. The water surface velocity and depth estimated from point measurements of water surface fluctuations were found to be in close agreement with the water surface velocity estimated from PIV data and actual water depth measurements. Furthermore, these values could be estimated from the water surface fluctuations.
