洪水流の非定常特性に関する研究

Abstract

洪水流はボイルや並列らせん流を含む三次元構造を有するとともに, 流れの非定常性という重要な特徴を持つ。本研究は, このような洪水流の特徴に着目して, 洪水の増水期と減水期の各段階において水面流況と河床形状の同時計測を繰り返し, 洪水流の乱流構造の非定常特性を河床形状との関連で把握しようするものである。洪水流の乱流構造の検討に際しては, 斐伊川における1997年の2回の洪水観測の結果が用いられた。

In the Hii River, the flow patterns on the flow surface during a flood stage were taken by video camera, and the three-dimensional river-bed configurations were measured by a echo-sounder attached to a cross-type float. Velocity vectors were calculated by applying two-dimensional cross-correlation method. The velocity distributions, the stream lines, the divergence distributions and the vorticity distributions were calculated by using the obtained velocity vectors.Based on the obtained data, the characteristics of boils, vortex motions and parallel spiral flows with longitudinal axes, wave height of dunes and their time variation during a flood were examined. Manning's roughness coefficient were calculated by using the obtained data, and it is found that Manning's roughness coefficient was maximum when the wave height of dunes reached the highest level.