A relation between the frequency distributions of sieve diameters and fall velocities is developed. The relation shows that if the sieve diameters of a sediment are log-normally distributed, the fall velocities will also have this distribution, but with a different standard deviation which can be calculated. The results of detailed measurements of the fall velocities of two different natural sands are presented, and the distributions of fall velocities are found to be in good agreement with the predicted distributions. The sedimentation diameters determined from the measured fall velocities agree very well with those predicted from the sieve diameters by the Inter-Agency Committee on Water Resources [1957]
