The Long Profile Flashcards
Upper course
Predominantly erosion
Vertical Erosion dominant, almost no depostion
Greater GPE
Middle Course
Predominantly transportation
Decreasing gradient
Lateral erosion (valley widening), some deposition
Lower Course
Deposition dominant
Alluvium deposition
Some lateral erosion
Concave shape
The steep reduction in height near the source gives way to a more gradual reduction further downstream, giving a typical concave profile.
Why is there more GPE in the upper course?
The river has much potential energy near the source due to the steep drop
Hydraulic action
The sheer force of the water breaks parts of the river banks through penetration of the cracks and gaps, forcing their breakdown.
Abrasion
Is the sandpaper effect of rocks grinding against the bed and banks.
Attrition
Rocks within the channel smash into each other and break up
Corrosion
When very fine mateiral is dissolved in the water, ususally Calcium Carbonate (limestone+chalk)
Consequence of corrosion
less material being carried by the river as very fine material is in a state of solution
Factors that affect rate of erosion
Weight of the water
Gradient of slope (water gains speed)
The height of the water, the greater the GPE it contains
Traction
large stones and boulders are rolled along the river bed by the water moving downstream
Saltation
Stones bouncing along the river bed- easily seen (bed load)
Suspension
Fine material is carried along by the river.
If river slows material can be dropped, causing build up of silt in river and canals.
Solution
material is dissolved in the water and is carried along by it.
River Transport
Solution
Suspension
Saltation
Traction
Reasons for deposition
Reduction in velocity
Sudden rise in river’s load e.g. landslide into river
Evaporation of water
Factors affecting fluvial processes
River volume
River speed/velocity
Slope
Width, Depth, of channel
Load
Erosion Processes
Hydraulic Action
Attrition
Abrasion
Corrosion
What is the Hjulstrom Curve?
Special type of graph that shows how a river’s velocity affects its competence and its ability to erode particles of different sizes.
What are the two curves with Hjulstrom?
a critical erosion velocity curve and a mean settling velocity curve.
What does the critical erosion velocity curve show?
shows the minimum velocity needed to transport and erode a particle.
What does the mean settling velocity curve show?
shows the minimum speed that particles of different sizes will be deposited by the river.
What do the shaded areas between the curves show?
the different process that will be taking place for particles that lie in those shaded areas.
What do the axis represent on the curve?
X- Particle size (mm)
Y- Velocity (cms1)
