Apparent Contact Angle Effects of Sand Layer on the Fingertip Velocity and Finger Width Formed during Rainfall Infiltration

Abstract

It is well known that water repellency of sand affects the hydrological process and soil erosion. However, detailed effect of sand wettability on the downward infiltration has not been clarified. We conducted rainfall infiltration experiments using sand samples with different contact angle to assess the relationship between the contact angle and the fingertip velocity and finger width. It was found that fingertip gained almost constant velocity in the sand layer with apparent contact angle from 50° to 75°, and that finger width showed the minimum value when the apparent contact angle was about 72°. Fingertip velocity became faster as the rainfall intensity became higher, but finger width showed only slight increase. We applied an existing model to estimate finger width, which did not explain the feature of finger width mentioned above though the model apparently well fitted to the measure values.