The most important stream process in defining channel form is the bankfull discharge, which is sometimes referred to as the effective discharge, or dominant discharge. For these reasons natural resource managers increasingly use natural channel designs to restore impaired streams.īankfull Stage and Discharge Skip to Bankfull Stage and Discharge Channel features like pools, riffles, steps, and undercut banks provide diversity of habitat, oxygenation, and cover. Trees and shrubs along the banks provide a food source and regulate water temperatures. In addition to transporting water and sediment, natural streams also provide the habitat for many aquatic organisms including fish, amphibians, insects, mollusks, and plants. (Each of these characteristics will be defined in this fact sheet.) The study of these interactions and the resulting streams and rivers is called fluvial geomorphology. All of these characteristics are related to the interactions among climate, geology, topography, vegetation and land use of the watershed. Other physical characteristics shared by some stream types include pools, riffles, steps, point bars, meanders, floodplains, and terraces.

Streams have left and right streambanks (looking downstream) and streambeds consisting of mixtures of bedrock, boulders, cobble, gravel, sand, or silt/clay. While streams and rivers vary greatly in size, shape, slope, and bed materials, all streams share common characteristics. The morphology, or size and shape, of the channel reflect all of these factors. Other factors which affect channel size and stream flow are land use, soil types, topography, and climate. The size and flow of a stream are directly related to its watershed area. Further downstream where baseflow is large enough to sustain stream flow throughout the year, perennial streams are formed. They dry up when groundwater levels drop. These streams are partially supplied by groundwater rising to the surface as stream baseflow. Downstream from ephemeral channels are intermittent streams, which carry water during wet times of the year. These are referred to as ephemeral channels that only carry water during rainfall runoff. As surface runoff moves downslope, it concentrates in low areas and forms small stream channels. When rain falls in a watershed, it either runs off the land surface, infiltrates into the soil, or evaporates ( Figure 1). The land area draining to a stream or river is defined as its watershed. Streams and rivers are integral parts of the landscape that carry water and sediment from high elevations to downstream lakes, estuaries, and oceans.

Downstream processes definition