Experiments on rain-induced incipient motion of noncohesive sediment

Laboratory studies of artificial raindrops demonstrate the importance of rain in sedimentation processes in the shallow intertidal zone. Drop-formed vortex rings are hypothesized to be a mechanism for transfering kinetic energy to bottom sediments. Vortex rings initiated sediment motion in shallow water at least 22.5-cm deep. Although rings were able to move very coarse sand, they were more efficient in moving the finer-sand sizes. The probability of drops initiating sediment motion decreased from 94 to 11% with increasing depth from 2.5 to 22.5 cm. Ring-induced bottom shear stresses were estimated in excess of 11 dynes cm^–2.