Numerical Simulation Of Groundwater Level Fluctuations In Coastal Confined Aquifers Induced By The Tide

Studies of groundwater motion in coastal aquifers are of important significance inreasonable development of groundwater resources and scientific management ofcoastal areas in building safe structures and underground project construction and inthe ecological environment protection. The research focus of this paper is on thedetermination of water level. Tidal sea levels fluctuation drives adjacent coastal waterlevel to vibrate and achieve dynamic stability after the cycle of average water level.The position obtained doves not consider higher steady-state level of tidal action,namely the inshore water level under the influence of ultra high tides. In the existingregional groundwater mathematical models, the tides caused by sea level fluctuationsis often ignored. The prediction of the location of the groundwater table and the actualsituation may be somewhat different.In this paper, numerical simulation is combined with the physical experimentcontrast analyses to find an equivalent of the coast and a method for determiningboundary condition. We described the tidal boundary within short time series into asine function form, and the tide for a long time sequence boundary is described as alimited form of Fourier series, to study the cyclical fluctuation characteristics underthe induction of tidal water level in coastal areas. This paper examines respectivelyfor the two circumstances, the no-leaky flow and the leaky flow to establish aone-dimensional mathematical model for describing the nearshore groundwatermovement. According to the inversion of the measured data of the model parameters,a three dimensional mathematical model is established and identified. The finitedifference method is used to discrete the model, and using a calculation program, thenumerical solution is obtained, and the numerical solution and the measured data arecompared. The results show that the coastal aquifer groundwater levels change withthe tide, groundwater levels affected by the tide in the coastal aquifer and the tidehave similar characteristics with the same period of T=24.7h. The amplitudeattenuation effect is obvious and the tidal efficiency decays with the distance from theshore with a negative exponent function attenuation. In the distance of500m from the coast, the amplitude is1.35268m, and tidal efficiency is0.54107. In the distance of2000m, the amplitude is0.26736m, and tidal efficiency is0.10694. Groundwaterlevels reach the peaks and valleys with a time lag effect. The time lag increaseslinearly with the distance from the caost. In the distance of500m from the coast, lagtime is1.825h, and in2000m distance, the lag time is9.825h. In the distance of4389m far from the shore, the groumdwater levels can be thought to not be affectedby the fluctuation of the tide. The initial water level and two kinds of linear tilt andnuances are considered, the tidal swings in farthest distance are also different. Theseconclusions may provide a reference basis for the reasonable evaluation ofgroundwater resources in coastal areas.