MECHANISMS TO MAINTAIN AND ANNIHILAITE WATERFALLS FORMED ON BEDROCK

Abstract

 A variety of water falls are commonly observed in rivers with exposed bedrock. Though it has been generally known that waterfalls are gradually migrating upstream, the details of the migration process has been left unclarified. In this study, we have conducted movable bed flume experiments with the use of mortar as the model of bedrock to understand mechanisms of upstream migration and maintainance of waterfalls formed on bedrock. We found from the experiments that, when the erosion rate in the upstream reach of a waterfall is dominant over that in the the downstream reach, the waterfall disappears. When the erosion rates in the upstream and downstream reaches of a waterfall are in balance, the waterfall does not disappear but is maintained. When the erosion rate in the downstream reach of a waterfall is dominant over that in the upstream reach, the waterfall increases its gap. In the development process, the waterfall migrates upstream with the formation of a series of waterfalls in the upstream vicinity.