Author(s): Iehisa Nezu; Hiroji Nakagawa

Linked Author(s): Iehisa Nezu, Hiroji Nakagawa

Keywords: No Keywords

Abstract: Aerial surveys of straight rivers and flow visualization in laboratory flumes suggestthat cellular secondary currents might existin wide,fluvial open-channel flows and that,at the same time,longitudinal ridges andtroughs of the bed material which are called"sand ribbons",might be formed periodicallyin the spanwise direction by these cellularsecondary currents. Kinoshita(1967)firstfound from aerial stereoscopic surveys offlooded rivers that a boil street with highconcentration of suspended sediment became alow-speed zone and high-speed zones in whichfoams gathered were formed on both sides in aspanwise direction,with a spacing of twicethe flow depth h.Fig.1 shows an example ofstereo-photogrammetric picture of the KisoRiver near Nagoya,Japan.The following esti-mątion was made;the water discharge Q=6700m³/s,the river width B=660 m,the waterdepth h=6m and the aspect ratio B/h=110.If one watches two photographs of Fig.1through stereograss,one can easily distin-guish the high-speed and low-speed zones,because the higher velocity of water surfacein which foams gather can be seen in morerising image due to Cameron's effect.

DOI:

Year: 1989