Rivers Flashcards
What are the three main parts of a river?
Upper course, Middle course and the Lower course.
What is Hydraulic Action?
The sheer force of the water dislodges particles from the river’s bed and banks.
What is Abrasion?
Smaller material carried in suspension (like sandpaper) against the banks of the river.
What is Corrosion?
When acid in the water dissolves the rocks (such as limestone).
What is Attrition?
Boulders and other material are transported along the bed of the river, these collide and break into smaller pieces.
Corrosion, Abrasion, Attrition and hydraulic Action are all types of what?
Erosion.
What is Traction?
Large rocks and boulders are rolled along the river’s bed.
What is Saltation?
Smaller rocks are bounced along the river’s bed.
What is Suspension?
Fine material, light enough, is carried along in the flow of the river (giving water its colour).
What is Solution?
Dissolved material eroded by corrosion is carried in solution.
Solution, Saltation, Traction and Suspension are all types of what?
Transport.
What happens when a rivers power is reduced?
The river dumps or deposits its load as it can no longer carry material.
When is a river’s power reduced?
-The flow of the river slows: This happen when the gradient of the river bed becomes less steep/more shallow, or when the water flows around thew inside of a bend.
-The volume of water in the river is reduced: This will happen if water is lost to evaporation or percolation.
What are some features of the Upper Course of a river?
-Steep Sided ‘V’ Shaped Valley
-Interlocking Spurs
-Rapids
-Waterfalls
-Gorges
P.S. which are all formed by erosion.
How is a ‘V’ Shaped Valleys?
-A small stream will naturally follow small depressions in the landscape.
-As the small stream flows downhill steeply, the bedload will erode downwards and scrape away the bottom of the channel (vertical erosion).
-This vertical erosion deepens the valley, making the sides steeper and exposed.
-Over time, weathering and gravity wear away the steep valley sides, forcing material into the stream, which it uses to cut the valley deeper.
When rivers get closer to the mouth what happens?
It gets increasingly wider and there are gentle sided valleys.
Why does the channel increase in size?
To hold extra water which it receives from its tributaries.
What happens in the middle course of the river?
The river starts to erode sideways (laterally) into its bank rather than downwards into its bed (vertically), like it does in the upper course.
What happens when rivers flow over flat land?
They develop large bends called Meanders.
What is the river beach?
The part of the meander where water flows slowly and deposits material.
What is the river cliff?
The part of the meander where water flows quickly and erodes the bank.
How is an Oxbow Lake formed?
-Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time.
-Erosion narrows the neck within the meander.
-In time and usually during a flood, the river will take a new shorter route.
-The new route will be fastest down the middle and therefore deposit material across the old meander.
-In this time, the bend will cut off becoming an Oxbow Lake.
What are some Physical causes of floods?
