A considerable amount of research has been done recently on the mechanism by which grains of sand, etc., may be picked up by a river or by a gale of wind and carried to some distance. In particular Jeffreys (1929) has considered the theoretical aspects of the action while the writer (1934) and Bagnold (1936) have published experimental data on the action by which the grains are picked up in water and air respectively. Another problem of considerable practical importance is th a t of the quantity—or, more strictly, the time average of the quantity—of solid material carried at different levels above the bed or ground. Up to the present, data on this question have all been collected in relation to a special case, i. e. that in which the particles have the same size and density. Thus, Hurst (1929) collected samples of uniformly graded sand at different depths in a turbo-cylinder containing a vigorously stirred mixture of sieved sand in water, and showed that, in the body of the cylinder, an exponential relation between “weight” of sample and height above the bottom of the vessel existed. The present paper is mainly concerned with measurements of the concentration of the suspended material near the uniformly graded bed of an artificial channel and the application of these results to the conditions in a natural stream.
The suspension of solids in a turbulent stream