Development of handy measurement system for river flow environment based on image-based technique

The understanding of river flow in various flow conditions is a crucial issue in managing river environment. To satisfy the requirement of such needs, river flow velocity and discharge have been measured from low to high flow conditions. The typical way to acquire such data has been to use either a probe-type current meter or the Acoustic Doppler Current Profiler (ADCP). However, due to the difficulty to use them in extreme flow conditions such as in huge floods, non-intrusive techniques to use video images have become available in recent years such as the large-scale image velocimetry (LSPIV) and the space-time image velocimetry (STIV). Despite a wide-spread use of these techniques, there remains some difficulties to use them in situations where conventional image-based methods are difficult to apply. In order to overcome the shortcomings of the conventional techniques, we developed a handy flow measurement system that uses a camcorder. In the system, a tripod installed a high-accurate clinometer is used to ortho-rectify obliquely viewed river surface images, which is used to obtain surface velocity distributions by LSPIV. The outstanding feature of the system is that the above image conversion and LSPIV analysis are performed not locally but on the web system provided by the co-author company. This enabled the measurement of river flow at any arbitrary flow conditions. Some examples of flood flow measurements demonstrated that the developed system is superior to the existing conventional techniques for river flow environment measurements.