Kinetics of Gravity-Driven Water Channels under Steady Rain

We investigate the physical mechanisms that govern the formation of water channels that develop from finger instabilities at the wetting front. Using controlled experiments in a quasi-2D cell and varying physical parameters (particle size, fluid viscosity, etc.), we simulate rainfall and characterize the homogeneous wetting front as well as channel size and estimate relevant time scales associated with the instability as well as channel velocity. We validate the results by developing a model based on linear-stability analysis with the addition of another term describing the homogenization of the wetting front. This shows that the way we introduce a fluid into a granular medium affects the formation of water channels. Results permit us to calculate the ideal flow rate for maximizing water distribution and minimizing runoffs using granular and fluid properties.