Flow and transport at the Las Cruces trench site

Two water flow and solute transport experiments were performed as part of a comprehensive field trench study near Las Cruces, New Mexico. These experiments were designed to provide data to test deterministic and stochastic models of vadose zone flow and transport. In Experiment 1, a 4 m by 9 m area was irrigated for 10 days with water containing tritium. Thereafter, water was applied without tritium for an additional 76 days. Simple one-dimensional uniform and layered soil deterministic models for infiltration adequately predicted the overall movement of the wetting front during infiltration, but poorly predicted point values for water content due to spatial variability. Use of the layered soil model, rather than the uniform soil model, did not consistently improve prediction accuracy, for this particular field application. In Experiment 2, a 1.22 m by 12 m area was irrigated for 11.5 days with water containing tritium and bromide. Thereafter, water was applied without tracers for an additional 64 days. Water and bromide moved fairly uniformly during infiltration, whereas high concentrations of tritium developed on one side of the irrigated area. During redistribution, tritium moved little, whereas bromide displayed significant movement both downward and to one side. A two-dimensional deterministic model for water flow showed qualitative, but not quantitative, agreement with observations. A two-dimensional deterministic model for solute transport poorly described tritium and bromide movement during redistribution. 24 refs., 25 figs., 4 tabs