Hydraulic Characteristics of a Doubly Meandering Compound Channel

This paper presents the hydraulic characteristics of a doubly meandering compound channel. The experiments are carried out in a 30 m long and 1.5 m wide tilting flume. One important feature of this doubly meandering compound channel is that there is a phase difference of 30° between the main channel and the outer levee. Two types of flow conditions are examined viz.: shallow water condition and deepwater condition. The water surface fluctuation, stream-wise velocity distribution and secondary currents are analyzed. It is found that the stream-wise velocity tends to deviate from floodplain to main channel and from main channel to floodplain. The degree of deviation is higher for shallow water condition than deepwater condition. The maximum deviation occurs at the cross-over section for both shallow and deepwater water condition. The exchange of flow between main channel and floodplain drives secondary flow cells in the main channel as well as in the floodplain. The anti-clockwise cell grows along the inner bank of the main channel, reaches its peak at a section in between the cross-over region and the bend apex next to the cross-over region and decays immediately upstream of the bend apex. The opposite thing happens in the next bend. The evolution and decay process of secondary currents is virtually the same for both shallow and deepwater condition. In case of shallow water condition the mound of water is observed along the main channel-floodplain interface and in case of deepwater water condition the mound is observed along the side of the flood levee.