ABSTRACT
It is an indispensable subject to understand the formation mechanism of the plane shape of a river channel, when considering maintenance of a river channel, and it serves as the basic point of river improvement or river environment. A meandering channel and a braided stream are generally mentioned as the plane shape of a river channel. Research on these formation mechanisms has been conducted. In rivers which formed multi-row bars or braided rivers, riverbanks often have wavy shape on a scale of several times of river width. In such rivers, a wide width part (anti-node) and a narrow part (node) appear by turns in the longitudinal direction. The elucidation of this phenomenon accompanied by bank erosion is very important on river management works. However, the formation mechanism of this gourd type channel has not been clarified. This research conducts a linear stability analysis including bank erosion phenomenon as the first step which clarifies the formation mechanism of such channel shape. It was shown that the observed longitudinal wavelength of the gourd type river channel is explained by this theory. It became clear that a gourd type wavelength becomes shorter than the wavelength of double-row bars formed in the fixed bank channels. Moreover the wavelength of this riverbank changes with the hydraulic conditions. The wavelength becomes long, when a non-dimensional shear stress or a non-dimensional particle diameter becomes large or a river width depth ratio becomes small.
