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

本文描述了河口高度分层流动中的非定常混合机理。在1997年和1998年对受潮汐影响的石卡里河(Ishikari River)下游45公里处的水位进行研究时，获得了以下数据：1)6个地点连续2个月的表层盐度自动记录：2)两个地点垂直线上6个深度的2周盐度；3)利用声波测深仪在三个地点测量了两个月的界面深度。研究结果表明：1)在半日潮期间，盐楔界面位置的变化幅度是潮差的n倍，从河口到上游约7公里处，n逐渐增加，然后逆转增加的趋势，在上游26公里处减小到约为零。最初认为，由于河流地形的影响，界面起伏在上游7公里处达到最大值，但原因尚不清楚。2)通过盐度垂直分布的观测，解释了表层盐度与风的关系。风的增加增加了盐分在界面上的扩散，而上层的盐分浓度梯度仍然很低。这意味着，由于风诱导的过程而带入上层的盐分立即通过该层分布；普通的扩散过程不能对此负责。3)在0~4m水深范围内，观测到了S和S分别以2.5m和10m~20m的周期波动。这两种波动都是由波浪作用引起的，但在观测到这些波动的任何时刻都没有界面，因此不可能是界面波引起的。

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.