大小潮作用下沿海潜水水位波动的数值研究

Numerical modeling of groundwater table fluctuations due to spring-neap tides in a coastal unconfined aquifer

沿海潜水层具有一个动态的向海边界,水位随海潮的波动而波动.浸润面的存在给向海边界条件的确定带来一定的困难,而以往研究(例如大小潮水位波动的摄动解法)往往忽略浸润面的影响.为此,在考虑浸润面影响的基础上建立了大小潮水位波动的数学模型.模拟结果表明:(a)潜水层周期平均水位高于静止水位;(b)大小潮向内陆传播时振幅衰减越来越明显,但传播距离远远大于半日潮的传播距离;(c)水位随时间变化具有不对称性,水位上升比下降快;(d)在水位下降阶段特别是大潮期间,地下水渗出点水位偏离潮汐水位,即会形成浸润面.

Groundwater tables in coastal unconfined aquifers interfaced with ocean by a moving boundary fluctuate with tides. It is difficult to determine the seaward boundary condition due to the existence of seepage face; however, the effects of seepage face are always neglected in previous research, for instance, in the perturbation solutions of water table fluctuations due to spring-neap tides. Thus, with the effects of seepage face taken into account, a numerical model for spring-neap tidal water table fluctuations is developed. The simulation results demonstrate that （1） the mean water table is higher than the still water table; （2） the fluctuations of spring-neap tides damp considerably as they move toward inland, but they spread much farther than that of the semi-diurnal tide; （3） local water table fluctuations are asymmetric, and the rising phase is much steeper than the falling phase; （4） the water table at exit points deviates from that of tides during the falling phase, especially during the spring tide period, leading to the formation of seepage face.