Exploratory study of sediment diffusion

Abstract

A study was made of the diffusion of glass beads in a submerged axisymmetric jet in order to compare the characteristics of the diffusion of sediment with those of the diffusion of momentum in free-turbulence shear flow. A vertical 1/4-inch jet of sediment-laden water was directed downward into a relatively large cylindrical tank of still water. Small concentrations of nearly spherical glass beads, both within and above the Stokes range in size, were introduced into the recirculating system. The efflux velocity of the jet was maintained at 20 ft/sec or more to lessen the relative importance of the fall velocity of the individual particles. Concentration profiles of the sediment were measured at various downstream sections in the zone of established flow and were compared with the velocity profiles at the same sections. The diffusion characteristics of the sediment-laden water were analyzed by use of the approximate theories derived for clear water jets. The results are applied to the suspended-load equation presently used for two-dimensional flow in open channels. Certain conclusions are drawn as to the propriety of the assumptions pertaining to the fall velocity and sediment diffusion used in deriving this equation.