Air concentration measurements in high-velocity spillway flows using LIDAR technology

• Measurements of aerated spillway flows with LIDAR positioned at seven locations. • Grazing angle between beam and surface affects measured elevation. • New correction scheme using air concentrations corrects LIDAR data independent of position. • LIDAR able to estimate total air concentration profiles and design parameters along spillway. • Next steps are measurements of more strongly aerated flows and in prototype structures. Accurate measurements of air-water flows are essential for understanding energy dissipation and ensuring safe operation of hydraulic structures, such as spillways. Traditionally, measurements in high-velocity aerated flows have relied on point-based techniques, such as intrusive phase-detection probes. Recently, Light Detection and Ranging (LIDAR) technology has emerged as a powerful tool for capturing high resolution, time-varying free-surface features of aerated flows with high accuracy. While most of this research has focussed on hydraulic jumps, the application of LIDAR technology to spillway flows has only been tested in a single study of a short spillway model. To assess the applicability of LIDAR technology for measurements on spillways more widely, this study conducted a comprehensive study of three skimming flows on a large-scale spillway model with strip roughness and slope of 10.8°. Seven different LIDAR positions were tested, revealing a strong effect of grazing angles on the measured free-surface properties. To address this, a new correction method for grazing angle induced distortions in raw LIDAR signals is proposed. The corrected LIDAR data accurately predicted air concentration distributions and characteristic flow depths, irrespective of the LIDAR position. These findings open opportunities for future applications at prototype scale, but additional research of more strongly aerated flows is needed.