TY - JOUR
T1 - Rain splash of dry sand revealed by high-speed imaging and sticky paper splash targets
AU - Furbish, David Jon
AU - Hammer, Katherine K.
AU - Schmeeckle, Mark
AU - Borosund, Miriam N.
AU - Mudd, Simon Marius
PY - 2007/3/24
Y1 - 2007/3/24
N2 - Rain splash transport of sediment on a sloping surface arises from a downslope drift of grains displaced ballistically by raindrop impacts. We use high-speed imaging of drop impacts on dry sand to describe the drop-to-grain momentum transfer as this varies with drop size and grain size and to clarify ingredients of downslope grain drift. The "splash" of many grains involves ejection of surface grains accelerated by grain-to-grain collisions ahead of the radially spreading front of a drop as it deforms into a saucer shape during impact. For a given sand size, splash distances are similar for different drop sizes, but the number of displaced grains increases with drop size in proportion to the momentum of the drop not infiltrated within the first millisecond of impact. We present a theoretical formulation for grain ejection which assumes that the proportion of ejected grains within any small azimuthal angular interval dθ about the center of impact is proportional to the momentum density of the spreading drop within dθ and that the momentum of ejected grains at angle θ is, on average, proportional to the momentum of the spreading drop at θ. This formulation, consistent with observed splash distances, suggests that downslope grain transport involves an asymmetry in both quantity and distance: more grains move downslope than upslope with increasing surface slope, and, on average, grains move farther downslope. This latter effect is primarily due to the radial variation in the surface-parallel momentum of the spreading drop. Surface-parallel transport increases approximately linearly with slope.
AB - Rain splash transport of sediment on a sloping surface arises from a downslope drift of grains displaced ballistically by raindrop impacts. We use high-speed imaging of drop impacts on dry sand to describe the drop-to-grain momentum transfer as this varies with drop size and grain size and to clarify ingredients of downslope grain drift. The "splash" of many grains involves ejection of surface grains accelerated by grain-to-grain collisions ahead of the radially spreading front of a drop as it deforms into a saucer shape during impact. For a given sand size, splash distances are similar for different drop sizes, but the number of displaced grains increases with drop size in proportion to the momentum of the drop not infiltrated within the first millisecond of impact. We present a theoretical formulation for grain ejection which assumes that the proportion of ejected grains within any small azimuthal angular interval dθ about the center of impact is proportional to the momentum density of the spreading drop within dθ and that the momentum of ejected grains at angle θ is, on average, proportional to the momentum of the spreading drop at θ. This formulation, consistent with observed splash distances, suggests that downslope grain transport involves an asymmetry in both quantity and distance: more grains move downslope than upslope with increasing surface slope, and, on average, grains move farther downslope. This latter effect is primarily due to the radial variation in the surface-parallel momentum of the spreading drop. Surface-parallel transport increases approximately linearly with slope.
UR - http://www.scopus.com/inward/record.url?scp=34249732010&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=34249732010&partnerID=8YFLogxK
U2 - 10.1029/2006JF000498
DO - 10.1029/2006JF000498
M3 - Article
AN - SCOPUS:34249732010
SN - 2169-9003
VL - 112
JO - Journal of Geophysical Research: Earth Surface
JF - Journal of Geophysical Research: Earth Surface
IS - 1
M1 - F01001
ER -