A reach is a continuous section of a stream or river. The stage of a flow is the elevation of the water surface. Stream channels contain alternating regions of riffles and pools. During low flows, riffles are regions of shallow, rapid flow. The velocity of water in pools is lower than in the riffles.
Meanders are freely-swinging, winding stream channels.
Meandering stream Topography describes the shape of a portion of the earth's surface including its elevations and the position of physical and cultural features. At bankfull stage , water flow fills a stream channel to the top of its banks just to the point where water begins to overflow onto the adjacent floodplain. Infrequent extreme floods may cause significant changes in stream channels. However, bankfull stage flows transport the greatest quantity of soil and stone over time, because the bankfull stage occurs about once every year or two. The bankfull stage is related to channel dimensions such as width, and to the meandering pattern of a stream.