A fast flux tube-based method for solute-transport simulation

A new method to calculate the transport of dissolved species in aquifers is presented. This approach is an extension of the stream tubes which are used for flow computation. The flux tubes defined here are conservative for solutes, but not for water mass. The flux tubes are first defined in a general domain and then calculated in a two-dimensional uniform flow field. The tubes’ computation is based on a parametric solution. The method is extended further in order to deal with heterogeneous media. A particle-tracking algorithm is used where the deviation of the flux-tube boundaries due to dispersion is accounted for. The approximate solution obtained by this approach is compared to classical numerical solutions given by a finite difference code (RT3D) and a finite element code (FEFLOW). This comparison was performed for several test cases with increasing complexity. The differences between the flux-tube approach and the other methods always remain small, even regarding mass conservation. The major advantage of the flux-tube approach is the ability to reach a solution quickly, as the method is hundreds to thousands of times faster than classical finite difference or finite element models.