河床表層粒度構成の不安定現象としての縦断交互分級の形成機構
1989 年 1989 巻 411 号 p. 143-150
詳細
1989 年 1989 巻 411 号 p. 143-150
In a stream composed sand and gravel, wavy patterns of sorting are often observed and they cause fluctuation of fractional bed-load discharge. In this paper, the formation mechanism of longitudinally alternate sorting is formulated as a linear instability analysis of bed-surface composition with a non-equilibrium bed-load transport model for each grain size of sediment mixture, and the condition that the longitudinal sorting falls unstable and predominant wave length of alternate sorting are predicted. As a result, alternate longitudinal sorting develops under the condition slightly above the threshold of motion of bed-material particles, and it always propagates downstream. The predominant wave length is subjected to the diameter of bed material, and thus its scale is the same order as small-scale bed forms. The theoretical results are consistent with the observed data.
