NUMETRICAL SIMULATIONS OF THE BEHAVIOR OF ALTERNATE BARS WITH DIFFERENT BANK STRENGTHS

This study examined the behavior of alternate bars in a channel with erodible banks by considering the effect of vegetation on bank strength. A two-dimensional model was developed to simulate the development of an initially straight channel with erodible banks composed of well-sorted sandy material. A moving boundary-fitted coordinate system was used to describe a natural shaped boundary. The flow field was calculated using the CIP method. To simulate bank erosion, it was assumed that banks eroded when the gradient in the cross-sectional direction of the banks was steeper than the submerged angle of repose, due to the bed erosion near the banks. The lateral rate of channel expansion, bar migration speed, and wavelength were studied numerically when the channel remained nearly straight. The bars migrated more slowly as the aspect ratio increased. The bars in a channel with strong banks migrated rapidly, and the dimensionless bar, expressed as bar height to water depth ratio, was higher than that of a channel with weak banks. Our numerical experiments showed that the behavior of bars differed according to bank strength under the same hydraulic conditions.