潮流沙脊的水力学问题探讨

A Probe into Hydraulic Problems about Tidal Current Ridges

借用河流水力学顺直河道中有两个次生横向环流的假说来解释潮流沙脊的成因，水槽实验和实际观察也支持了这一观点．正是这一次生的纵轴横向环流（即螺旋流）将泥沙从沟槽带向脊顶，建造了大致与潮流方向平行的潮流沙脊．根据底质粒度成份和分布特点．可分为粗底质沙脊和细底质沙脊两类．前者组成物质偏粗，底质分布为脊细槽粗，后者组成物质偏细，底质分布为脊粗槽细．这是因为影响颗粒起动流速的主导因素不同，前者以重力为主，后者以颗粒间粘结力为主．它们都反映沟槽中流速大于脊顶处流速．

The hypothesis that these is a pair of secondary transverse circulations with longitudinal axes (spiral currents)in a straight river is used to explain the formation mechanism of tidal current ridges. Flume experiments and actual observation also support this view.It is just this seeondary transverse circulation that moves sands from the swale between ridger to the crest of the ridge and builds the tidal current ridger which run roughly perallel to tidal current. Based on the grain size and distribution of sediments, tidal current ridges are divided into 2 type: One type is the ridge coarse bed material with fine edments on the crest and coarse ones in the swale, the other is the ridge of fine bed material with coarse sediments on the crest and fine ones in the swale. Because the dominant factors affecting the threshold velcity are different, gravity is dominant in the former, intergranular cohesive force in the latter. Both of them reflect that the velocity of tidal current in the swale is stronger than that over crest.