Kinetics of gravity-driven water channels under steady rainfall

Abstract

We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasi-twodimensional experimental setup composed of a random close packing of monodisperse glass beads.Using controlled experiments, we analyze the finger instabilities that develop from the wetting front as a function of fundamental granular (particle size) and fluid properties (rainfall, viscosity). These finger instabilities act as precursors for water channels, which serve as outlets for water drainage. We look into the characteristics of the homogeneous wetting front and channel size as well as estimate relevant time scales involved in the instability formation and the velocity of the channel fingertip. We compare our experimental results with that of the wellknown prediction developed by Parlange and Hill [D. E. Hill and J. Y. Parlange, Soil Sci. Soc. Am. Proc. 36, 697 (1972)]. This model is based on linear stability analysis of the growth of perturbations arising at the interface between two immiscible fluids. Results show that, in terms of morphology, experiments agree with the proposed model. However, in terms of kinetics we nevertheless account for another term that describes the homogenization of the wetting front. This result shows that the manner we introduce the fluid to a porous medium can also influence the formation of finger instabilities. The results also help us to calculate the ideal flow rate needed for homogeneous distribution of water in the soil and minimization of runoff, given the grain size, fluid density, and fluid viscosity. This could have applications in optimizing use of irrigation water. We investigate the formation of fingered flow in dry granular media under simulated rainfall using a quasitwo-dimensional experimental setup composed of a random close packing of monodisperse glass beads. Disciplines Physical Sciences and Mathematics | PhysicsUsing controlled experiments, we analyze the finger instabilities that develop from the wetting front as a function of fundamental granular (particle size) and fluid properties (rainfall, viscosity). These finger instabilities act as precursors for water channels, which serve as outlets for water drainage. We look into the characteristics of the homogeneous wetting front and channel size as well as estimate relevant time scales involved in the instability formation and the velocity of the channel fingertip. We compare our experimental results with that of the well-known prediction developed by Parlange and Hill [D. E. Hill and J. Y. Parlange, Soil Sci. Soc. Am. Proc. 36, 697 (1972)]. This model is based on linear stability analysis of the growth of perturbations arising at the interface between two immiscible fluids. Results show that, in terms of morphology, experiments agree with the proposed model. However, in terms of kinetics we nevertheless account for another term that describes the homogenization of the wetting front. This result shows that the manner we introduce the fluid to a porous medium can also influence the formation...

Rain water transport and storage in a model sandy soil with hydrogel particle additives

“…If there is more than one channel, what sets the separation length? To help answer such questions, a quasi two-dimensional version of our set-up has been constructed in order to to directly visualize channel morphology and kinetics [31,32].…”

Morphology of Rain Water Channeling in Systematically Varied Model Sandy Soils

“…It is hard to say whose prediction may be better from here. More detailed discussion regarding their models is given later in this paper when examining the effects of the soil grain diameter and surface wetting property and also in our kinetic study paper [19].…”

“…Lastly, we discuss irrigation efficiency improvement methods that relate to the rain water channeling phenomenon and demonstrate their effectiveness under different circumstances. In a companion paper, we study the kinetics of rain water channeling [19].…”

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