Morphology and Flow in Streams

Abstract

Streams are characterized by a continual downstream movement of water, dissolved substances, and suspended particles. These components are derived primarily from the drainage basin or watershed*, which is the total land area draining into a given stream channel. Thus the hydrological, chemical, and biological characteristics of a stream reflect the climate, geology, and vegetational cover of the drainage basin[cf., Beaumont (1975), Likens, et al. (1977), Hynes, (1970), Oglesby et al. (1972) and Whitton (1975)]. Water from rain or snow, falling on hilly or mountainous terrain, actually follows diverse routes in moving downhill (Fig. 5.1). Precipitation first may be intercepted by vegetation, then by litter on the surface of the ground. When water is added to the surface of a soil more rapidly than it can soak in (i.e., the infiltration capacity is exceeded) it will run off overland. Normally, most of the water from precipitation infiltrates into the soil. Soils have variable capacity to store water depending on depth, structure, composition, and other factors. Before stream flow can occur, this storage capacity must be exceeded. Storage capacity continually is made available by evaporation and transpiration (evapotranspiration). Until recently, limnologists have ignored, for the most part, the importance of hydrologic flow paths in regulating the metabolism and biogeochemistry of streams and lakes, as well as their role in the historical generation and accumulation of lake sediments [see Likens (1984)].

In American usage, watershed is equivalent to drainage basin or the European term, catchment, all of which refer to the region or area drained by a river system.