EXERCISE 5
Morphology and Flow
in Streams
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 ofthe drainage basin[ cr., 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)].
Flow through the soil may be channeled by soil
structure and features such as cracks, worm or
other animal burrows, and old root channels.
Impermeable layers can impede the vertical
movement of water and cause lateral flow at
intermediate depths in the soil (Fig. 5.1). The
chemistry of precipitation may be altered considerably as the water passes through a terrestrial
drainage basin ecosystem (Likens et aI., 1977;
Likens 1984). The surface of the saturated zone of
permeable soil is called the water table; water in
the soil above the water table is termed vadose
water and that below the water table, ground
water. Ground water provides the relatively
stable base flow component in streams. Overland
flow, in addition to water that infiltrates the soil
and then flows laterally to the stream channel
(i.e., subsurface storm flow), are the main components of peak flows or floods [cr., Dunne (1978),
Chorley (1978)].
*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.
55
Morphology and Flow
in Streams
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 ofthe drainage basin[ cr., 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)].
Flow through the soil may be channeled by soil
structure and features such as cracks, worm or
other animal burrows, and old root channels.
Impermeable layers can impede the vertical
movement of water and cause lateral flow at
intermediate depths in the soil (Fig. 5.1). The
chemistry of precipitation may be altered considerably as the water passes through a terrestrial
drainage basin ecosystem (Likens et aI., 1977;
Likens 1984). The surface of the saturated zone of
permeable soil is called the water table; water in
the soil above the water table is termed vadose
water and that below the water table, ground
water. Ground water provides the relatively
stable base flow component in streams. Overland
flow, in addition to water that infiltrates the soil
and then flows laterally to the stream channel
(i.e., subsurface storm flow), are the main components of peak flows or floods [cr., Dunne (1978),
Chorley (1978)].
*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.
55