Picture Analysis of Aerial Photographs of Flood Flows

A pair of aerial photographs of the flood flow in the Agano River on Sept. 25, 1966 was analyzed by the cross-correlation technique to obtain velocity vectors over the area of 1700 × 1000 m of the water surface. About 340 × 400 velocity vectors were obtained at every 5.0 m in streamwise and 2.5 m in spanwise direction.The interval and arrangement of the longitudinal low-speed band and high-speed band appearing alternately in the spanwise direction over the water surface were analyzed and two kinds of spanwise scales of large scale turbulence were found; one is about twice water depth and another is 4 5 times.