PREDICTION OF CONTAMINANT CONCENTRATION UPSTREAM OF GROUNDWATER FLOWS : AN INVERSE MASS TRANSFER PROBLEM

摘要

A numerical study is made of the inverse mass transfer problem in groundwater flows. Of particular interest is the prediction of the upstream contaminant concentration when measurements of both concentration and its gradient are obtained at some downstream location . To predict the concentration distribution upstream of the measurement location, the space marching finite-difference method is used. The instability associated with the ill-posedness of the problem, i.e. the oscillations of the solution due to random errors in the measured data, is treated by the mollification technique with a low-pass filter . Several numerical examples are presented to show the accuracy of the proposed algorithm. It appears that the present method may faithfully predict the contaminant concentration rather far away from the measurement location if random errors in the given data are carefully smoothed by an appropriate filter.