Deltas consist of three physiographic parts called the upper delta plain, the lower delta plain, and the subaqueous delta. The upper delta plain begins as the river leaves the zone where its alluvial plain is confined laterally by valley walls. When the valley wall constraint ends, the river breaks into a multitude of channels, and the depositional plain widens. This point source of the upper delta plain can be thought of as the apex of the entire delta, which is analogous to the same reach of an alluvial fan. The entire upper delta plain is fluvial in origin except for ...(100 of 32811 words)