Modelling studies for determining unsaturated flow components in a sandy soil during dual tracer test

摘要

Tracer methods combined with mathematical modeling are used as highly recommended techniques to investigate flow and transport phenomena in the subsurface. In the present paper such methods were applied to a dual tracer test for estimating discharge processes in the unsaturated zone of a heterogeneous sandy soil. From pressure head measurements mean lateral and mean vertical water fluxes have been obtained, where horizontal flow component could be neglected in the further analysis. Deterministic modeling of unsaturated vertical flow and transport, based on estimated hydraulic functions and hydrodynamic dispersion from breakthrough curves (BTC's) only agreed for pressure head simulations but not for temporal distribution of deuterium and bromide. Additional stochastic simulations of dual tracer transport showed plausible and well comparable results, if unsaturated dispersion was obtained from a constant mean dispersivity and a random distributed water velocity.