抄録
Experimental studies on the mode of movement, stability, and transportation of sedimentary particles are described, and the following points are clarified:(1) In the deposition of saltant particles, they come to a stop after the process of traction, while suspended particles do so without perceptible traction., When settled particles are set in motion again, the processes are reverse., (2) The critical condition required for saltation is given as follows: d/V4≒1., 5×l0<-9> (c·g·s) at 7., 5°C., The letter d is the diameter of a particle and V is the current velocity near the bottom., However, in case d less than about 0., 1mm., the particle stays in suspension., (3) If V is a little greater than the critical current velocity required for the traction of sorted aggregate particles, the traction of the individual particle is repeated intermittently, but after a little while this traction comes to a stop and the sedimentary particles, on the whole, become stable., In this case, the smaller the size or the fewer the quantity of the sedimentary particles, the longer the time required to attain stable conditions., (4) The V required to remove the stabilized particles may be regarded as a critical current velocity required for erosion (cf., part 3)., If d is less than about 0., 1mm., this velocity becomes large with the elapsed time after the deposition., (5) The above stabilization is due to compaction by settling of the sediment, and this causal action increases abruptly when d becomes about 0., 1mm., or less., (6) On the unstabilized bed the transported (or eroded) quantity 'Tw ' of bed material varies not only with V but also with d of bed particles, namely Tw is expressed as follows: Tw∽V-(4log10d+1)(c·g·s) at 10°C., As stated above, it must be noticed that d≒0., 1mm., is a kind of critical point of abrupt changes in the phenomena related to the sedimentation process and that this d also corresponds to one of the critical points of 'settling velocity' or 'proper critical velocity of current' (cf., part 2).,
