The analysis of this paper may be summarized as follows: 1. Streams, as an integrated part of a drainage basin, assume their characteristics in accordance with the hydrographic and geologic conditions of the basin. Giving the material which forms the boundary of the channel, the form and gradient of an alluvial river are functions of the amount and hydrograph of water and sediment carried to the reach from the upstream watershed. 2. When the capacity of the stream channel to carry the bed-material load is different from the amount of the load brought in by the watershed, erosion and depo- sition result. After self-adjustments of long duration, many of the alluvial rivers are able to carry the water and sediment imposed on them by the basin, and approach a condition of equilibrium or quasi-equilibrium. The sediment carrying capacity of these rivers actually represents the timed average of the sediment production rate of the upstream basin.