Measurement of Inundating Flow From a Broken Enbankment by Using Video Images Shoot From a Media Helicopter

Abstract

The heavy rain disaster in the Kinugawa River basin that occurred along with the passage of the Typhoon 18 caused the embankment destruction in the middle reach of the river on September 10, 2015. Due to the overflow, the houses in the vicinity of the embankment collapsed, causing a flood inundation spreading over a wide area. Because the embankment breakwater occurred during the daytime, the state of the inundating flow was recorded from various angles by media helicopters or drones. In this study, we developed a method to extract quantitative flow information from a helicopter video image in which the shooting position and angles are changed one after another, because it was taken in emergency. In the analysis, the images were orthorectified after stabilizing the images, from which surface velocity distributions were measured by image-based technique such as the large-scale particle image velocimetry (LSPIV) or the space-time image velocimetry (STIV). As a result, the time change of water entering from the broken embankment and the total inundated water volume during the disaster were estimated. In addition, two-dimensional surface velocity distributions were analysed to show the spreading of inundated flow.

An Evaluation of Image Velocimetry Techniques under Low Flow Conditions and High Seeding Densities Using Unmanned Aerial Systems

“…Large-Scale Particle Image Velocimetry (LSPIV), the first image velocimetry technique to be introduced in outdoor environments, was originally developed by Fujita (1997) which applies the principles of the classic Particle Image Velocimetry (PIV) techniques to fluvial field conditions (large-scale) [11]. Image velocimetry has been successfully used to monitor river flow in many different applications, for example, crowd sourced data has been used to calculate the flow of a flash flood in the French Alps [1], 2D flow fields have been assessed for hydraulic engineering applications [12], and discharges flowing through a broken embankment during a large snow-melt flood in Japan have been calculated [13]. Since the introduction of LSPIV, various other algorithms have been developed which adopt alternative approaches for the calculation of surface flow velocity (Table 1).…”