The long profile of a river is a way of displaying the channel slope of a river along its entire course.
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Where in the course is there more turbulence?
Generally, in the upper part of the long profile or Thalweg there is more turbulence, lots of bed load in comparison to discharge and lots of roughness and fiction.
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What happens when more streams and tributaries join the river?
As more streams and tributaries join the river, roughness decreases, discharge and velocity increases and the erosive power of bed load will decrease.
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What happens as a result?
As a result the gradient of the river will generally decrease creating a concave long profile with distance down stream, and deposition serves to enhance this phenomenon further.
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What is erosion in the upper course normally like?
Erosion in the upper valley is generally straight down into the bed, and vertical, helping to keep gradient steep.
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What is erosion in the lower course like?
In the lower reaches erosion is lateral or side to side, reducing gradient and further enhancing the concave long profile.
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What is base level?
Base level is the lowest level to which erosion by running water can take place.
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What is it generally accepted as?
This is generally accepted as sea level, but local base levels can arise when rivers enter an inland sea or lake, where a tributary enters a bigger river or where a resistant band of rock crosses a valley.
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What is grade?
Grade is the concept of a river being in equilibrium, with a balance between the rate of erosion and deposition.
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Why is this balance constantly upset?
This balance is constantly upset by changes in discharge and sediment load, and can alter over long periods of tie because of changes in Base Level.
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Why can rivers change across their channels?
Also, rivers can change across their channels, where variable discharges and loads cause channels to shift position and shape to adjust to these changing characteristics. Base level can change in many ways
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What is potential energy in relation to rivers?
In relation to rivers, potential or (stored) energy is fixed by the altitude of the source of the stream in relation to base level.
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What is kinetic energy in relation to rivers?
Kinetic energy, or energy due to movement, is generated by the flow of the river which converts potential energy into moving energy.
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What is the amount of kinetic energy determined by?
The amount of kinetic energy is determined by the volume of flowing water (discharge), the slope or channel gradient down which it is flowing and its average velocity. An increase in velocity and/or discharge results in an increase in kinetic energy.
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What are all channel process dependent on?
All channel processes are dependent on the amount of energy available. This is a delicate balance.
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What happens if there is excess after transportation?
If there is excess after transportation of load the river will erode, but if energy is insufficient to move the load deposition will occur. The river channel adjusts in shape and size to accomadate changes in the volume of water and sediment.
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What is cross profile?
The valley cross profile is the view of the valley from one side to another. For example, the valley cross profile of a river in a upland area typically has a Vshape, with steep sides and a narrow bottom.
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What is the cross profile like in the upper course?
A narrow steep-sided valley where rivers occupies all of the valley floor. This is a result of dominant vertical erosion by the river.
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What is the cross profile like in the middle course?
A wider valley with distinct valley bluffs, and a flat floodplain. This is as a result of lateral erosion, which widens the valley floor.
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What is the cross profile like in the lower course?
A very wide, flat floodplain in which the valley sides are difficult to locate. Here there is lack of erosion, and reduced competence of the river, which results in large-scale deposition.
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Other cards in this set
Card 2
Front
Where in the course is there more turbulence?
Back
Generally, in the upper part of the long profile or Thalweg there is more turbulence, lots of bed load in comparison to discharge and lots of roughness and fiction.
Card 3
Front
What happens when more streams and tributaries join the river?
Back
Card 4
Front
What happens as a result?
Back
Card 5
Front
What is erosion in the upper course normally like?
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