Author(s): G. M. Tarekul Islam; Yoshihisa Kawahara; Nobuyuki Tamai
Linked Author(s): Yoshihisa Kawahara, Nobuyuki Tamai
Keywords: Secondary flow; Meandering; Unsteady
Abstract: Natural rivers, being predominantly meandering, are usually composed of a deep main channel and adjacent shallow floodplains. This results in a meandering compound channel. When the main meander channel is flanked by floodplains with meandering levee, it results in a doubly meandering compound channel. This study explores the secondary flow structures in a doubly meandering compound channel under unsteady flow condition. At the bend apex section, a clockwise cell develops in the main channel near the interface of the main channel and left floodplain while a clockwise cell develops near the levee of the left floodplain. As the flow approaches downstream, both the clockwise cells in the main channel and left floodplain grow in size and a new anticlockwise cell develops in the left floodplain near the interface of the main channel and left floodplain and a small anticlockwise cell develops in the left bank of the main channel near the bed. As the flow approaches further downstream, the clockwise and anticlockwise cells in the left floodplain start decaying and disappear in the cross-over region. The anticlockwise cell in the main channel near bed of the left bank continues to grow while that near interface disappear and a new anticlockwise cell develops in the main channel near the bed of the right bank. Following the cross-over region, the anticlockwise cell in the main channel near the bed of the left bank completely disappears and the other anticlockwise cell in the main channel near the bed of the right bank grows. At the next bend apex section, the secondary flow structures and the secondary flow cells are same as of previous bend apex section but in the opposite direction. The mechanism of the evolution and decay of secondary cells during rising and falling stages is the same but only differs in strength.
Year: 2007