中規模河床形態の形成条件

Abstract

The formative conditions of meso scale river bed configuration have not been clarified under highratio of the stream depth to the grain size h/d conditions, because of the scarcity of observed datawith precise hydraulic conditions due to difficulties in the execution of experiments.In this paper, however, experiments were conducted under the conditions of h/d>10 2, andresults of the experiments are mentioned about characteristics of sand bars and micro scale bedconfiguration as well as hydraulic conditions. The sand bars were classified by means of thegeometrical characteristics and of the formative process. Their formative conditions indicate a limitof the applicability of previous criteria for the bar formation obtained from bar data in the flat bed.Physical meanings of this limit are considered on the viewpoints of the initial height of the disturbedbed in order to extend the applicability of the authors' criterion. As a results of this consideration, amodified criterion is proposed, which takes effects of the sand waves in the lower regime into accountby using their height instead of the grain size. This criterion is examined by a few results observedand is discussed from the difference between the formative process of the bar in the flat bed and thatin the ripple bed. Furthermore, a difference of this concept from stability theories of the bedvariation and upper limits of the tractive force for the bar formation is discussed.