APPLICATION OF FLUX-CORRECTED TRANSPORT TO THE LAS-CRUCES TRENCH SITE

A flux-corrected transport (FCT) based numerical algorithm is develope d to model the solute transport equation in heterogeneous variably sat urated soils. The fully Eulerian algorithm is designed to model very s teep gradients without the characteristic numerical diffusion/dispersi on found in standard finite difference schemes. This algorithm can han dle both small and infinite grid Peclet numbers but is limited to grid Courant numbers less than or equal to 0.5. Since useful results can b e obtained for infinite Peclet numbers, the algorithm can be used to t race water movement when coupled with a numerical model for Richards' equation. We used the FCT based algorithm in conjunction with Richards ' equation to model a hypothetical experiment at the Las Cruces Trench site. In this numerical experiment, water with tracer is applied acro ss the top of a 24-m-wide domain. The two-dimensional distribution for the hydraulic properties estimated during site characterization is us ed to define the soil model. The predicted flow and tracer transport i s quite complex. The movement of the wetting front appears to be heavi ly influenced by the old water, whereas the new water tends to bypass much of the old water indicating preferential flow.