Three-dimensional Numerical Simulation Of Seawater Intrusion Based On The Finite Difference Methods

Seawater intrusion is a serious problem in coastal regions all over the wor ld,which occurs when the groundwater in coastal aquifers is over-abstracted, as a resultdegrades the water-quality by raising salinity to levels exceeding the acceptabledrinking water standards. It is of great significance to ascertain the width of transitionzone and make clear the amount of salinity and establish their varying patterns ofseawater intrusion using numerical methods. However, the impact of fluctuation ofsea lever was never accounted for in the past researches. So, this paper includes a partof the sea area and takes into consideration of the fluctuation of sea lever to a firstapproximation, which is an innovation.Firstly, the governing equation of flow that describes the water flow motion, andthe governing equation of solute transport that describes the law of moving andspreading of pollutants, are both derived by taking into account of the variation offluid density based on the law of mass conservation. Finally, the seawater intrusionproblem of the new campus of Dalian Ocean University is discussed in the light of theabove theory, using Visual MODFLOW that is international advanced and domesticpopular. Then the distinctions of the groundwater table elevation, the flow field, thewidth of transition zone and the salinity are analyzed in the condition with andwithout the seepage proofing.The results show that the groundwater table elevation in the new campus iselevated because of the increase of resistance, which is imposed on the groundwaterflow with the rise of sea level. And appreciations of both the width of transition zoneand the salinity are not the same between the first5years and the last5years of thesimulation time, indicating that the speed of seawater intrusion is not proportion to thesimulation time. In addition, the seepage proofing has an effect to boost thegroundwater table elevation, reduce the velocity of groundwater flow, shrink thewidth of transition zone and decrease the concentration of salinity. However, sucheffect is not very sharp, demonstrating that the seepage proofing can only put off thetime when the seawater intrudes into the new campus, but can’t block the salinity onthe outside of the schoolyard. Only looking for other more effective measures can wesettle the problem of seawater intrusion fundamentally.