COMPARISON OF CHARACTERISTICS OF HORIZONTAL EDDIES IN DIFFERENT RIVER CHANNEL BY AERIAL PHOTOGRAPHS

Abstract

Horizontal large eddies caused by the instability of shear layer between main channel and flood plain were investigated for two rivers by aerial photo analysis and numerical flow simulation. One river (A) has flood plains on both sides of main channel, and the other (B) has one flood plain with a comparatively narrow main channel. Transverse velocity at the edge of flood plains caused by eddies were obtained from aerial photo analysis, and eddy lengths were determined by zero-up cross of the velocity. A flow model of quasi-3D was applied to the large eddy computation under the actual flow conditions. Scale and intensity of eddies obtained from the computation agreed very well with the results from aerial photo analysis. In addition, the both results suggested that rows of eddies in river-A were less stable with frequent merging and splitting than in river-B. A series of numerical experiments showed that the eddy stability is controlled by the ratio of the transverse scale of eddies to the width of main channel.