RESEARCHES ON BED-LOAD TRANSPORTATION UNDER THE TRACTIVE FORCE NEAR THE CRITICAL LIMIT

Abstract

As an essential subject for the sake of treating theoretically the problem of sediment transport under the tractive force on the bed of river, it is very important to clarify the mechanism of the formation of sand ripples on the bed in the case of bed-load transportation. In other words, it is necessary to know how sand ripples occur and develop according as the condition of flow and the properties of bed sediment. As a fundamental research for this purpose, the writer experimentally mad clear the flow phenomena of bed load movement by using the sand bed without ripples, at the states such as the sand ripples were not yet occurred on the bed or the ripples were hardly generated in the case of using some kind of sands and theoretically analysed the results obtained. Finally he obtained the following conculusions.(1) Near the critical tractive force, the bed load movement is able to be treated as a kind of fluid motion, and under such way of thinking the writer introduced the formulas concerning the sediment transport in the case where the ripples were not generated. From the results obtained by using the formulas it can be said that the rate of sediment transport under the tractive force near the critical limit show some widely aport tendency According to the grain size of sand composing the channel bed.(2) The effect of ripple on the rate of sediment transport is quite different whether thee grain size of the sand constituting the channel bed is larger or smaller as compared with the critical size of 0.075cm in diameter. And, furthermore, the sand the size of which is near this critical diameter is easily to be moved owing to the characteristics belonging to the sand itself.