Laboratory Test And Numerical Simulation On The Prevention Of Seawater Intrusion By Underground Dam

The rapid development of population and economy recently have brought some serious contradiction between freshwater resources supply and demand. Saltwater intrusion in littoral plain areas has absorbed universal attention all over the world. The underground dam is one of effective engineering measures for the prevention of seawater intrusion. It can prevent saltwater intrusion effectively through cutting intrusion channels of sea water and discharge passage of fresh water. International experts have done laboratory tests on saltwater intrusion, but few was about underground dam. In this study, we simulated processes of saltwater intrusion with underground dam and without. Also a numerical simulation was presented on seawater intrusion process by using FEFLOW, so as to guide the prevention and the large scale numerical simulation of seawater intrusion and.The main working contents in this study as following:(1)The choice of colorant. Carmine with low adsorbability was selected preliminarily as the colorant for this study. Then interference test and solute transport were carried out to judge if carmine was are suitable.(2)Determination of simulation parameters. Related parameters of the test medium, suchas permeability coefficient, dispersivity, porosity, were determined by experiments. In this study, one-dimensional column model was disigned to determine permeability coefficient and dispersivity. Then porosity was determined.(3)Laboratory tests of saltwater intrusion without underground dam. Dynamic changes of saltwater intrusion interface were simulated without underground dam by using laboratory sandbox model.Coloring technology, Image process and water quality detection were used to simulate effects of the water heads and concentrations of saltwater on transport velocity of freshwater-saltwater interface.(4)Laboratory tests of saltwater intrusion with different underground dams. Control effects of underground dams with different permeability coefficient were simulated.(5)Numerical simulation. Sandbox model experiments were numerical simulated then carried on the fitting to the experimental date and simulated data to adjust parameters.The following conclusions are drawn in the paper.(1)Carmine was suitable for application to laboratory tests of saltwater intrusion.(2)Simulation parameters were determined.permeability coefficient was 0.22cm/s; vertical dispersivity was 0.0083m; porosity was 32.86%.(3)When there was no underground dam, the rate of movement of reshwater-saltwater interface decreased with time in each saltwater intrusion process; the higher the salt-water head or the saltwater concentration, the higher the rate of intrusion was; it can be predicted that the smaller the salt-water head, the more shorter the time reached equilibrium; the longer the time, the larger the transport velocity difference caused by saltwater concentration.(4)Permeability coefficient had great influence on saltwater intrusion. The smaller the permeability coefficient, the more obvious the effect was. When permeability coefficient reached 10-6m/s or above, the underground dam can control saltwater intrusion effectively.(5)According to the fitting situation of experimental data and numerical simulation, some parameters was adjusted the horizontal permeation coefficient was 1×10-2cm/s;the vertical hydraulic conductivity was 0.1×10-2cm/s.