Pressure Fluctuation at the Soil Surface and Photographic Analysis of Behavior of Soil Particles by the Impact of a Falling Waterdrop

A raindrop of natural rain falls with terminal velocity at the soil surface. In the laboratory, however, it is difficult to simulate actual rainfall, so experiments must be conducted with waterdrops which do not reach terminal velocity. This paper shows how the effect of drop size and impact velocity on the maximum pressure at the soil surface was experimentally investigated. The results of the experiments indicated that dimensionless parameters made by drop size, impact velocity and impact pressure were closely related to each other. It seems possible therefore to change the pressure force of the impact of a waterdrop which has fallen from a comparatively low height for that of the impact of a raindrop. In order to reveal the mechanism of soil erosion, the effects of a fallen waterdrop on soil particles and surface water were recorded using high-speed camera (16mm) and single-lens reflex camera (35mm). The photoanalysis helped explain the phenomenon of a fallen waterdrop digging a hole which is then filled by the splashed soil particles.