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  • Filtering of Period Infiltration in a Layered Vadose Zone: 1. Approximation of Damping and Time Lags

    • Authors: Dickinson, J.E.;  Advisor: -;  Participants: Ferré, T.P.A. (2018)

  • To represent geologically realistic systems, we used vertical sequences of one‐dimensional periodic solutions, where each solution represents a single soil in a layered profile. The overall approach is based on a linearized Richards equation and assumes that the effects on flow of continuous pressure head changes at soil interfaces are negligible. We evaluated the limit of these approximations by comparison with results from the numerical model HYDRUS‐1D, which uses the full Richards equation. We compared (i) the depth at which flux variations became steady, and (ii) the travel time of wetting fronts to reach a depth of 3 m. The solution was reasonably accurate (error less than a fact...
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  • Long‐Term Soil‐Water Tension Measurements in Semiarid Environments: A Method for Automated Tensiometer Refilling

    • Authors: Smith, J.B.;  Advisor: -;  Participants: Kean, J.W. (2018)

  • Tensiometer‐equipped data acquisition systems measure and record positive and negative soil‐water pressures. These data contribute to studies in hillslope hydrology, including analyses of rainfall runoff, near‐surface hydrologic response, and slope stability. However, the unique ability of a tensiometer to rapidly and accurately measure pre‐ and post‐saturation subsurface pressures requires maintenance techniques that have precluded their application to unattended sensor networks in semiarid regions. Under suction, the de‐aired water in the tensiometer is drawn from a porous cup. Under positive pressure, dissolved gases from pore water infiltrates the cup. Over time, both contribute t...
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  • Measuring Soil Water Content with Ground Penetrating Radar: A Decade of Progress

    • Authors: Klotzsche, A;  Advisor: -;  Participants: Jonard, F.; Looms, M.C.; van der Kruk, J.; Huisman, J.A. (2018)

  • Tremendous progress has been made with respect to ground penetrating radar (GPR) equipment, data acquisition, and processing since the establishment of GPR as a tool for soil water content determination in vadose zone hydrology about 25 yr ago. In this update, we aim to provide a critical overview of recent advances in vadose zone applications of GPR with a particular focus on new possibilities for multi‐offset and borehole GPR measurements, the development of quantitative off‐ground GPR methods, full‐waveform inversion of GPR measurements, the potential of time‐lapse GPR measurements for process investigations and hydrological parameter estimation, and recent improvements in GPR inst...
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  • Method for Controlling Temperature Profiles and Water Table Depths in Laboratory Sediment Columns

    • Authors: Tokunaga, T.K.;  Advisor: -;  Participants: Kim, Y.; Wan, J.; Bill, M.; Conrad, M.; Dong, W. (2018)

  • Transport from the soil surface to groundwater is commonly mediated through deeper portions of the vadose zone and capillary fringe, where variations in temperature and water saturation strongly influence biogeochemical processes. This technical note describes a sediment column design that allows laboratory simulation of thermal and hydrologic conditions found in many field settings. Temperature control is particularly important because room temperature is not representative of most subsurface environments. A 2.0‐m‐tall column was capable of simulating profiles with temperatures ranging from 3 to 22°C, encompassing the full range of seasonal temperature variation observed in the deep ...