Numerical Experiment Study On The Influence Of Tide To The Estuary Saltwater Intrusion

The estuary has rich natural resources, it’s also the water source for the local residents to live and produce. At present, the phenomenon of saltwater intrusion in estuary has made a bad influence on society. In recent years, the saltwater intrusion has intensified in the several large estuaries of our country. Therefore, study on the related problems of saltwater intrusion is very necessary and meaningful.There have many factors affect the saltwater intrusion, this paper used the Delft3 D software to set up a three-dimensional channel model, by simplifying river geometry,reducing the influence of other factors, under the condition of constant runoff, only study the tide effect on the saltwater intrusion distance.The main research contents and results are as follows:(1)Using the saltwater intrusion distance formula of Dyer and Prandle to completed the feasibility analysis of the model.(2)Have studied the effects of main tidal constituents on the movement of salt water.Found that under different constituents conditions, the movement of saltwater is different,there are two different phenomena about the distance of saltwater intrusion, one is that the distance of saltwater intrusion is larger in the spring tide period and smaller in the neap tide period, the other is that the distance of saltwater intrusion is larger in the neap tide period and smaller in the spring tide period.(3)Have studied the relationship between the two different phenomena with the main tidal type and tidal range. Found that whether the semidiurnal tide or the diurnal tide, with the change of partial tide, the distance of saltwater intrusion can behave as larger in the neap tide than in the spring tide period, also can behave as larger in the spring tide than in the neap tide period. The analysis shows that compared with the tidal type, the relationship between the tidal range and the two different phenomena is more close.(4)Based on the sine wave, have studied the influence of tidal range to saltwater intrusion. Found that under the experimental conditions:(1)when there is no tide, the distance of saltwater intrusion is farthest;(2)exist critical tidal range that makes the distance of saltwater intrusion minimum, when the tidal range is less than the critical tidal range, thedistance of saltwater intrusion decreases with the tidal range increases, when the tidal range is greater than the critical tidal range, the distance of saltwater intrusion increases with the tidal range increases;(3)At the same time, the critical tidal range is the demarcation point of saline stratification phenomenon, when the tidal range is greater than the critical tidal range, salt water showed strong mixing type. Point out, when there is no tide, the main driving force of saltwater intrusion is density difference; when the tidal range is small, the transport mode of saltwater is mainly the effect of gravity circulation; when the tidal range is large, the transport mode of saltwater is mainly the effect of tidal diffusion.(5)For the tide which has semi-monthly changed of semidiurnal tide and diurnal tide,through the critical tidal range, established a method to judging the saltwater intrusion phenomenon under the tidal conditions.