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  • BB

  • Forward prediction of early‐time spontaneous imbibition of water in unsaturated rock fractures

    • Authors: Perfect, E.;  Advisor: -;  Participants: Brabazon, J.W.; Gates, C.H. (2020)

  • This study compared forward predictions of early‐time displacement of air by water within Mode I fractures in 14 low‐porosity rock cores using a new fractal model with those based on an established parallel plate model. Spontaneous imbibition was measured using dynamic neutron radiography, along with independent determinations of equilibrium contact angle, fracture aperture width, and fracture surface fractal dimension, Ds. The predicted uptake curves generally agreed with the experimental data. However, both models overpredicted the height of the wetting front at any given time. This overprediction may be due to lateral losses of wetting fluid to the matrix by spontaneous imbibition through fracture surfaces. The predictions of the fractal model were consistently closer to the obse...
  • BB

  • Quantification of hydraulic redistribution in maize roots using neutron radiography

    • Authors: Hayat, F;  Advisor: -;  Participants: Zarebanadkouki, M.; Ahmed, M.A.; Buecherl, T.; Carminati, A. (2020)

  • We show how to use neutron radiography to quantify the rate of water efflux from the roots to the soil. Maize (Zea mays L.) plants were grown in a sandy substrate 40 cm deep. Deuterated water (D2O) was injected in the bottom wet compartment, and its transport through the roots to the top dry soil was imaged using neutron radiography. A diffusion–convection model was used to simulate the transport of D2O in soil and root and inversely estimate the convective fluxes. Overnight, D2O appeared in nodal and lateral roots in the top compartment. By inverse modeling, we estimated an efflux from lateral roots into the dry soil equal to jr = 2.35 × 10−7 cm−1. A significant fraction of the redistributed water flew toward the tips of nodal roots (3.85 × 10−8 cm3 s−1 per root) to sustain their g...
  • BB

  • The effect of the top soil layer on moisture and evaporation dynamics

    • Authors: Li, Z.;  Advisor: -;  Participants: Vanderborght, J.; Smits, K.M. (2020)

  • Results show that the top soil layer can significantly affect the evolution of soil moisture profiles and evaporation dynamics, the extent of which depends on the layering sequence, thickness, and properties of each layer. The soil systems consisting of a thick coarse (C) layer overlying a fine (F) layer, or a very thin F layer overlying a C layer exhibit near‐surface moisture, temperature and fluxes nearly identical to that of a homogeneous C system; in these cases, a homogeneous C soil could be used to represent the above two layered systems. However, some soil profiles cannot be described by a single set of soil properties, nevertheless, they show distinct characteristics that can serve as indicators for soil layering conditions, e.g., “first slowly then rapidly” decreasing dynam...
  • BB

  • Analytical expressions for noncapillary soil water retention based on popular capillary retention models

    • Authors: Streck, T.;  Advisor: -;  Participants: Weber, T.K.D. (2020)

  • Recently, Weber et al. proposed a new model for noncapillary retention of soil water without introducing new parameters. The model is based on the integral of any given saturation function for the capillary part in log space. In the original paper, the integration was carried out numerically. Here, we derive analytical solutions for the most popular soil water retention models (van Genuchten, Kosugi, and Brooks–Corey).