2024 年 1 巻 p. 17-35
River discharge is one of the most difficult hydrological quantities to measure both accurately and safely and several novel methods have been searched for in the past decades in addition to the conventional float method. The space-time image velocimetry (STIV), which measures streamwise surface flow velocity distributions from video images can be one of the candidates to meet the above requirements. However, as long as the measurement target is a surface flow, there raises a problem to be solved when converting the surface velocity distribution to discharge via the surface velocity coefficient α, because the standard value of 0.85 does not always provide an adequate discharge in practice. To improve the versatility of discharge measurement with STIV, the maximum entropy method (MEM) was utilized to derive a general equation for the surface velocity coefficient, taking into account the velocity dip phenomenon and wind effects. The applicability of the proposed method was demonstrated through application to two rivers, the Ohta River and the Nakamura River. The discharge estimated by the proposed method agreed well with the discharges measured by the acoustic Doppler current profiler (ADCP) which is considered to provide the most reliable data, and gave better results than those estimated by the conventional laws of vertical velocity distribution. A sensitivity check of the entropy parameter in flow estimation was also performed.
