Entrainment Phenomena in a Stratified Flow with Average Velocities and Turbulent Surface Layers

本文描述了河口高度分层水流的非定常混合机制。这里考虑的因素包括风、潮汐、流量和外部诱导的湍流（来自波浪）。1997年和1998年对石笠河下游45公里处受潮汐影响的水位进行了以下资料的研究：1)6个地点连续2个月的地表盐度自动记录；2)两条垂直线上六个深度的盐度，持续两周；3)界面深度，使用声波测深仪，在三个地点进行两个月。研究结果表明：1)在半日潮期间，盐楔界面位置变化幅度为潮差的n倍；从河口到上游约7 km处，N逐渐增加，然后逆转增加趋势，在上游26 km处减小至零左右。最初认为，由于河流的拓扑结构，界面波动在上游7 km处达到最大值，但原因尚不清楚。2)地表盐度与风的关系已由盐度垂直分布观测得到解释。增大的风增强了盐在界面上的扩散，而上层的盐浓度梯度仍然很低。这意味着由于风引起的过程而被带入上层的盐立即通过该层分布；普通的扩散过程不能对此负责。(3)在水深0 ~ 4 m处，流速波动周期为2.5 s和10 ~ 20 s。这两种波动都是由波的作用引起的，但在观察到这些波动的任何时候都没有界面，因此它们不可能是由界面波引起的。

This report describes unsteady mixing mechanisms in highly stratified flow at river mouths. Wind, tide, flowrate and externally induced turbulence (from waves) are the factors considered here.The following data were taken in studies of the lower 45 km of the Ishikari River, whose level is affected by the tide, in 1997 and 1998: 1) Automatic recordings of surface salinity for two months at six locations; 2) salinity at six depths in a vertical line for two weeks at two locations; 3) depth of the interface, using a sonic depth finder, at three locations for two months.The results of the studies are summarized as follows: 1) During semidiurnal tides, the amplitude of the variation in position of the salt wedge interface is n times the tidal difference; n increases gradually from the mouth to about 7 km upstream, then reverses the increasing trend, diminishing to about zero at 26 km upstream. It was originally thought that the interface fluctuation reaches a maximum at 7 km upstream due to river topology, but the reason remains unknown. 2) The relation of surface salinity with wind has been explained by the observations of vertical salinity distribution. Diffusion of salt across the interface is augmented by increased wind, while the salt concentration gradient in the upper layer remains very low. This means that the salt entrained into the upper layer due to wind-induced processes is immediately distributed through the layer; ordinary diffusion processes can not be responsible for this. 3) Fluctuations in river flow speed with periods of 2.5 s and 10 - 20 s were observed between 0 and 4 m depth. Both fluctuations arise from wave action, but there was no interface at any of the times these fluctuations were observed, so they can not be caused by interface waves.