Abstract: In order to surmount the difficulty of numerical dispersion and numerical oscillation an improved characteristic finite element method is presented to solve the highly nonlinear sea water intrusion problem.The solved three-dimensional mathematical model,which regards exchanging cations Na⁺ and Ca²⁺ as simulation factor,takes account of cation exchange reaction between water and rock.The simulated results are satisfactory by comparison with the field data,and show that this model can be applied to predict the movement and evolution of exchanging cations during sea water intrusion.

Key words: Improved characteristic finite element method, Sea water intrusion, Cation exchange, Numerical simulation