Longitudinal river profile
As flow longitudinal profile of a flux is defined as the Gefällslinie its water level from the source to the orifice . It is divided into upper, middle and lower reaches.
Details
Most rivers have a concave profile . In nature, this idealized longitudinal profile is often interrupted by kink points. There there is a deviation from the originally concave shape and thus a change in gradient (e.g. waterfalls ). Breakpoints usually arise at tectonic faults or where the rock bedrock changes, and with it the strength of the erosion . The gradient, and thus the flow velocity, usually decrease towards the lower reaches.
Upper course
The upper course is the section of a river or stream near the source , often leading through relatively well-profiled terrain. Compared to the other sections, there are usually the deepest valleys here. The upper course is the most oxygen-rich section, but poor in nutrients ( oligotrophic ).
Deep erosion takes place on steep slopes and at high flow speeds. Rinsing and excavation result in a lowering of the river bed (the river eats its way deep into the slopes, large debris is carried away). Erosion channels form. Constant rubbing and grinding results in deeply sunk valleys with almost vertical walls in the upper reaches of erosion channels. Depending on how steep their slopes are, one speaks of a gorge or a gorge . With reduced flow velocity and increased side erosion, V-shaped notch valleys develop .
Middle course
With a low gradient and low flow velocity, there is accumulation (deposition of river cargo), at the same time side erosion takes place (lateral erosion on the embankments). The river bed is widened and bottom valleys are formed . The river freight only includes small and now rounded stones and sand.
Lower course
The section of a river or stream near the mouth , often leading through comparatively flat terrain, is called the lower reaches or Potamal . Compared to the other sections, there are usually the gentlest valleys here. It is low in oxygen and has absorbed many nutrients ( eutrophic ).
When the flow rate is slow, the transported rock (rubble, sand, mud layers) accumulates .
Deposits predominate in the lower reaches (e.g .: silt and sand). The low-gradient river branches out ( cf. Delta ), creating meanders and floodplains that are flooded by floods.
