Field Study of Multidimensional Flow and Transport in the Vadose Zone

A comprehensive field experiment was conducted to determine geologic controls on water flow and solute transport in a heterogeneous vadose zone. The experiment was conducted on a 10-m by 10-m plot underlain by heterogeneous beds of clays, sands, gravels, and cobbles of alluvial and fluvial origin. The plot and surrounding area were instrumented with 21 neutron probe access tubes, 168 tensiometers, and 62 solution samplers. Steady water application was provided by a drip irrigation system. Measurements of subsurface wetting and drainage, a multitracer transport experiment, in situ and laboratory determinations of hydraulic parameters, and destructive geologic characterization were conducted. The results of all determinations reflected the extreme short-scale geologic variability of the subsurface material. Attempts to model the flow and transport behavior were only partially successful.

The project provided a detailed characterization of a vadose zone typical of those found throughout the western U.S. The extensive data base developed under controlled conditions may be useful for future modeling activities.