Deposits formed in the lee of ripples, dunes, and deltas are essentially a case of diffusion developing in a turbulent re-attaching half-jet of low speed with normal gravity. A brief physical exploration is made of behavior of grains under these conditions. Given knowledge of sediment discharge and local properties of sediment load, the rate of settling of grains downstream from the sand-body crest is regarded as a function of the time-average and fluctuating properties of the flow. The central tendency of grain distribution depends on mean properties of motion. The distribution is likely to be skewed toward the larger values of downstream distance and the point of maximum deposition rate lies close to the crest of the sand body. The distribution can be represented by a formula given here.