DISCHARGE MEASUREMENTS OF FLOOD FLOW BY IMAGING TECHNOLOGY AND FLOAT METHOD

摘要

Accurate evaluation of flood discharge is of great importance in projects regarding river basin management and channel design. In most cases, measurement of river flow discharge has been performed by means of rather a primitive method using floats thrown from a bridge. The float method, which is based on a simple principle, is still useful and applicable to various flood conditions. However, the float method could have some shortcomings with respect to its accuracy because floats thrown on the surface of flood flow with strong turbulence cannot always follow the main flow faithfully. In addition, it becomes even dangerous to supply floats from a bridge in case of a serious flood. Consequently, a more sophisticated and safe method is required and it is proposed in this research to use two imaging techniques for measuring surface velocity distributions and flood discharges; Large-Scale Particle Image Velocimetry (LSPIV) was used for daytime measurements and Particle Tracking Velocimetry (PTV) using light floats was employed for measurements during the night. In the present field measurements, the conventional float method and the imaging methods were used at the same time for measuring a snow flood occurred in the U-River in Japan. The accuracy and applicability of the measurement methods are discussed in detail.