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UNSTEADY FACTORS AFFECTING SALT DIFFUSION IN THE STRATIFIED FLOW SYSTEM AT A RIVER MOUTH

影响河口层流系统盐分扩散的不稳定因素

基本信息

批准号：
04452231
负责人：
YOSHIDA Shizuo
金额：
$ 3.26万
依托单位：
Hokkaido University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1994
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-04452231/
关键词：
River Mouth Stratified Flow Two-Layr Flow Salt Diffusion Salt Wedge Entrainment Coefficient Interfacial Instability 界面不安定多層流界面波

项目摘要

The problem of salt diffusion in highly stratified flows such as those found at the mouth of a river is vital to considerations of agriculture and fisheries. Placement and control of the gates governing extraction of fresh water from a river have become social issues. Previous research has assumed that these flows are steady, and has focussed on problems of shear instability in the vicinity of the interface and natural turbulence. The research described below has examined these flows from the practical standpoint of whether and to what extent unsteady factors such as atmospheric pressure, tide, river flowrate, and wind affect salt diffusion around the river mouth. Those results have been used to attempt to develop an expression for improving predictions of the salinity of the river surface at any given point and time.These studies have been carried out mainly in the lower basin of the Ishikari River, Hokkaido, which is typical of a highly stratified flow. Observations were carried out … More in the summers of 1992,1993 and 1994 for about two months each. The observation methods were improved year by year and enough qualitative and quantitative data have been taken to fulfilll the research goals described above. The results of our research are as follows :1) Wind is the dominant factor in the surface salinity of a river. 2) The average entrainment coefficient of the salt wedge is given by the following formula : E = 1.92 * 10^<-6>e^<0.405^^W> for 118m^3/sec, E =2.24*10^<-6>e^<0.281^^W> for 146m^3/sec 3) The process of diffusion of salt from the salt wedge to the surface of a river has been shown to be the following : Wind blows>waves are generated>the turbulence in the upper layr increases>the distribution of salt in the upper layr is rendered uniform>the density gradient around the interface increases>the salt diffusion across the interface increases>the surface salinity increases. 4) The time average profiles of the flow system are stable throughout almost the entirity of the stratified flow system. 5) The process of diffusion is accelerated by an increase in river flowrate, but the salinity of the river water flow itself decreases. 6) Bridge piers and protuberences in the river bottom cause great disruptions in the interface, but the effect of these disruptions on salt diffusion is localized. 7) In order to predict the present surface salinity at any location it is sufficient to have an hourly record of wind speed along the river course and the discharge rate. Less

高度分层的水流（例如河口的水流）中的盐扩散问题对于农业和渔业的考虑至关重要。控制从河流中抽取淡水的闸门的设置和控制已成为社会问题。先前的研究假设这些流动是稳定的，并重点关注界面附近的剪切不稳定问题和自然湍流。下面描述的研究从实际角度检验了这些流动，即大气压力、潮汐、河流流量和风等不稳定因素是否以及在多大程度上影响河口周围的盐扩散。这些结果已被用来尝试开发一种表达式，以改进对任何给定点和时间的河流表面盐度的预测。这些研究主要在北海道石狩河下游流域进行，该流域是典型的高度分层流。观测工作于 1992 年、1993 年和 1994 年的夏天进行，各持续约两个月。观测方法逐年完善，并取得了足够的定性和定量数据，以实现上述研究目标。我们的研究结果如下：1）风是河流表面盐度的主导因素。 2) 盐楔的平均夹带系数由以下公式给出： E = 1.92 * 10^<-6>e^<0.405^^W> for 118m^3/sec, E =2.24*10^<-6>e^<0.281^^W> for 146m^3/sec 3) 盐从盐楔扩散到河流表面的过程已证明如下：风冲击>产生波浪>上层湍流增加>上层盐分分布均匀>界面周围密度梯度增加>界面上盐分扩散增加>表面盐度增加。 4) 流系统的时间平均分布在几乎整个分层流系统中是稳定的。 5）河流流量的增加加速了扩散过程，但河流水流本身的盐度却降低了。 6)桥墩和河底的突出物对界面造成很大的破坏，但这些破坏对盐扩散的影响是局部的。 7) 为了预测任何地点当前的表面盐度，每小时记录沿河道的风速和流量就足够了。较少的