1 Application of an automated discharge imaging 2 system and LSPIV during typhoon events in Taiwan 3

An automated discharge imaging system (ADIS), a non-intrusive and safe approach, was 12 developed for measuring river flows during flash flood events. ADIS consists of dual cameras to 13 capture complete surface images in the near and far fields. Surface velocities are accurately measured 14 using the Large Scale Particle Image Velocimetry (LSPIV) technique. The stream discharges are then 15 obtained from the depth-averaged velocity (based upon an empirical velocity-index relationship) and 16 cross-section area. The ADIS was deployed at the Yu-Feng gauging station in Shimen Reservoir upper 17 catchment, northern Taiwan. For a rigorous validation, surface velocity measurements were 18 conducted using ADIS/LSPIV and other instruments. In terms of the averaged surface velocity, all 19 measured results were in good agreement with small differences, i.e., 0.004 to 0.39 m/s and 0.023 to 20 0.345 m/s when compared to those from acoustic Doppler current profiler (ADCP) and surface 21 velocity radar (SVR), respectively. The ADIS/LSPIV was further applied to measure surface velocities 22 and discharges during typhoon events (i.e., Chan-Hom, Soudelor, Goni, and Dujuan) in 2015. The 23 measured water level and surface velocity both showed rapid increases due to flash floods. The 24 estimated discharges from ADIS/LSPIV and ADCP were compared, presenting good consistency 25 with correlation coefficient R = 0.996 and normalized root mean square error NRMSE = 7.96%. The 26 results of sensitivity analysis indicate that components till (τ) and roll (θ) of the camera are most 27 sensitive parameter to affect the surface velocity using ADIS/LSPIV. Overall, the ADIS based upon 28 LSPIV technique effectively measures surface velocities for reliable estimations of river discharges 29 during typhoon events. 30