Abstract
To understand more detailed phenomena from our previous study on bedrock exposer expansion under condition that bedrock is smooth and alluvial cover thickness is about half of bar height, flume experiments were conducted. In the case that bedrock was smooth and flow was maintained for longer hours than our previous study, the result showed that bedrock exposures along bar front were expanded to downstream on mid and upper side of flume and bedrock exposers along bar front were reduced on lower side of flume. This phenomenon was also confirmed by our previous study. Thereafter, new bars were developed on the upper end of flume and this new bars development caused exposing bedrock along bar front and these new bedrock exposers expanded to downstream. As this new bedrock exposer expanded to downstream side, expanded bedrock exposers on the immediate downstream of new bedrock exposers reduced. Thereby, as characteristics of bar wave lengths under condition that alluvial thickness is thin and bedrock is smooth, bar wave length is not stable. In another case that bedrock was as rough as alluvial cover materials, the results showed that bedrock expansion was reduced in comparison of the previous case. However, bedrock exposer rates were not notably different because total length of alternate bar is almost same between each case.
