Physical (Long profile) Flashcards
In general, what is the long profile of a river
It is usually smoothly concave, with the gradient being steeper in the upper course + becoming progressively gentler towards the mouth
How are irregularities in the gradient (which frequently occur) sometimes represented
As rapids, waterfalls and lakes
What are knickpoints
Marked breaks/changes in the slope of the long profile of a river, which is generally the product of rejuvenation
How does dynamic equilibrium occur
Irregularities in the long profile are eventually worn away by river erosion to give a smooth graded profile
What is dynamic equilibrium
Where balance has been achieved between processes of erosion and deposition
What do some geographers say about how a graded profile is achieved
They say it is when the river uses up all of its energy in the movement of water and sediment so that no free energy is left to undertake further erosion.
But if the volume and load of the river change over the long term, the river channel and its long profile will adjust to new conditions.
What is long profile (of a river)
It illustrates the changes in altitude of the course of the river
Which stage of the river has the most energy
Lower (as it is wider and there is more water increasing the velocity and therefore energy)
What does hydraulic radius show
The efficiency of the channel (ability is the channel to move water)
How do you calculate hydraulic radius
X-Sectional area / wetted perimeter
The higher the hydraulic radius..
The higher the efficiency
What is wetted perimeter
The length of the ned and banks in contact with the water
What is channel shape
The size of the channel (width : depth ratio) - it increases downstream
In which part of the river does velocity increases
Downstream
Why does velocity increase downstream
Upper course- narrow and shallow so a large proportion of the water is in contact with the bed and banks thus hydraulic radius is low; whereas in the lower course the channel becomes wider and deeper.
Although the wetted perimeter increases, there is less water in contact with bed + banks compared to cross area
