Flow Cell with High-Resolution Spatial and Temporal Degree of Saturation Measurements for Two-Dimensional Near-Surface Phenomena Using Unsaturated Transparent Soil

Abstract

Abstract Laboratory and field studies examining climate-ground-infrastructure interactions are often limited by spatial or temporal resolution, or both, of subsurface moisture content measurements. Laboratory control and field measurement of surficial and basal boundary conditions is performed rather straightforwardly; however, the interpretation of laboratory results may be limited by a lack of instrumentation or mislocated instrumentation. Computational modeling provides numerical results to compare with the physical data, but model calibration can be limited by the few instrumentation points. This article presents a new intermediate-scale apparatus to apply digital image analysis to unsaturated transparent soil experiments, which provides spatial resolution that is six orders of magnitude greater than traditional instrumentation and allows statistical quantification of saturation variability. The capabilities for saturation measurements in unsaturated transparent soil in two-dimensions are displayed using open and closed infiltration experiments. The two-dimensional (2D) experiments agree with column infiltration results showing air confinement decreases infiltration rate and wetting front mobility by more than one half. The 2D saturation measurements allow direct visualization and quantification of an unstable wetting front as well as dynamic moisture migration within the transmission zone. The 2D apparatus allows for development of behavior that is not possible in column apparatuses. Rather than the average, one-dimensional results are representative of the leading infiltration fingers in the 2D case. High spatial resolution saturation measurements show detectable influence of thin heterogeneities on wetting front migration. The influence of flow direction on saturation distribution is statistically quantified. High-resolution saturation measurements in an intermediate-scale apparatus allow new insight into near-surface flow processes.