Kinetics of gravity-driven water channels under steady rainfall

Area of Science:

• Physics of granular materials
• Fluid dynamics in porous media
• Soil science and hydrology

Background:

• Fingered flow, or preferential flow paths, significantly impacts water movement and solute transport in soils.
• Understanding the formation of these channels is crucial for effective water management and irrigation strategies.

Purpose of the Study:

• To investigate the formation of fingered flow in dry granular media under simulated rainfall.
• To analyze finger instabilities as a function of granular (particle size) and fluid properties (rainfall, viscosity).
• To compare experimental findings with the Parlange and Hill model and identify discrepancies.

Main Methods:

• Utilized a quasi-two-dimensional experimental setup with a random close packing of monodisperse glass beads.
• Conducted controlled experiments varying particle size and fluid properties.
• Analyzed wetting front morphology, channel size, instability timescales, and fingertip velocity.

Main Results:

• Experimental results on finger instability morphology align with the Parlange and Hill model.
• A new term accounting for wetting front homogenization was identified, influencing instability kinetics.
• The method of fluid introduction to the porous medium affects finger instability formation.

Conclusions:

• The study provides insights into the mechanisms governing fingered flow in granular media.
• Identified factors influencing homogeneous water distribution and runoff minimization.
• Results can inform optimized irrigation practices for enhanced water use efficiency.