The purpose in writing these notes has been to present a discussion of a few topics central to a physical understanding of the mechanics of sediment movement. Discussion has been confined to unidirectional flows (excluding waves) of relatively small scale (excluding Coriolis effects). A large number of topics have been not considered at all or only in passing, including one of the most important problems in sediment mechanics: theories for the prediction of bed-load and suspended-load discharge. It seemed more important to try to develop some physical insight about the elementary processes of sediment movement than to attempt to elaborate any comprehensive quantitative theories of sediment movement.