Application of Image Technique to Water Depth measurement of Dam-Break Flow

In recent years, dams around the world suffered from dam-break problems due to several extreme weather conditions such as typhoon events. Dam-break releases water with high velocity and rapid water level variation is found at the downstream of dam. Water depth measurement of dam-break is difficult using traditional method, such as point gauge. Recently the video device with high capture frequency is well developed. In addition, image technique is widely applied to flow measurement. Particle Tracking Velocitmetry, for instance, is popular to identify 3D position of particle with high velocity. Therefore, in this study, we apply image technique to measure water depth variation at the downstream of dam. To measure rapid water depth variation, experiments in flume are performed. The flume dimensions are presented in Figure 1. Flow of dam-break is simulated by suddenly lifting the gate. A laser beam locates at the center-line of the flume and gate. A 30-fps digital camera with a fixed angle of depression is placed at side of the flume. Coordinate transformation between image and space is first performed and image analysis is then used to identify the spatial water surface position from captured images. The validation of image technique is considered by measuring water depth using point gauge at a steady flow released from the gate. Three cases are considered in this study. The initial water depths at the upstream side of dam are 5, 10 and 15 cm and the bed is fixed at the downstream side. The measured water depth variations at x = 10 cm to ensure the measurements, numerical model, NTU-SFM2D, is used to simulate the experiments. The comparisons between experiments and simulations verify the application of image technique to rapid water depth variation at the downstream side of dam-break. Dimensions of experimental flume