Fluvial processes

Question 1

What is a drainage basin

Answer 1

A drainage basin is an area of land which is drained by a river.

Question 2

Draw the different types of transportation

Answer 2

https://bam.files.bbci.co.uk/bam/live/content/z3rf4j6/medium

Question 3

What is a tributary

Answer 3

A small river that joins the main river channel

Question 4

What is a confluence

Answer 4

The point at which two rivers meet

Question 5

What is a main river channel

Answer 5

The feature in which the river flows

Question 6

What is a water shed

Answer 6

The imaginary line which surrounds a drainage basin

(an area of highland which divides two drainage basins)

Any rain falling outside the watershed, will flow into another river basin

Question 7

What is the Hjulstrom curve

Answer 7

It is a graph that shows the relationship between sediment size and the velocity needed to erode, transport or deposit

Question 8

What are the types of transportation

Answer 8

Traction
Saltation
Suspension
Solution

Question 9

Describe the process of traction

Answer 9

This is when, heavy pebbles are rolled along the river bed. This is most common near the source of a river, as here the load is larger.

Question 10

Describe the process of suspension

Answer 10

This is when lighter sediment is suspended (carried) within the water, most commonly near the mouth of the river

Question 11

Describe the process of saltation

Answer 11

This is when pebble-sized particles are bounced along the river bed, by the force of the water.
Most commonly near the source

Question 12

Describe the process of solution

Answer 12

This is when soluble materials (e.g. limestone) dissolve in the water and are carried along

Question 13

State some reasons why rivers slow down and deposit material

Answer 13

The volume of the water falls
The amount of eroded material increases
The water is shallower e.g. on the inside of a bend
The river reaches its mouth

Question 14

What is deposition

Answer 14

Deposition is when a river drops the material it is transported

Question 15

When does deposition occur

Answer 15

Deposition occurs when a river loses velocity and energy

Question 16

Explain how particle size affects how far material is transported and where in a river’s course it’s deposited

Answer 16

Smaller particles are transported further and deposited closer to the river’s mouth

Question 17

State some formation of landforms resulting from erosion

Answer 17

Interlocking spurs, waterfalls and gorges

Question 18

Describe the formation of a waterfall (+ gorge)

Answer 18

The river may flow over an area of hard rock with softer more easily eroded rock underneath

Over time, the softer rock is eroded more rapidly than the hard rock by processes of hydraulic action and abrasion. This creates a ‘step’ in the river.

As the water flows over the step, it erodes more and more of softer rock

A steep drop is eventually created, which is called a waterfall

The hard rock is eventually undercut by erosion. It becomes unsupported and collapses.

The collapsed rocks are swirled around at the foot of the waterfall where they erode the softer rock by abrasion. This creates a deep plunge pool.

Over time, more undercutting causes more collapses. The waterfall retreats upstream, leaving behind a steep-sided gorge

Question 19

What is a gorge

Answer 19

Over time, because of erosion and deposition,
meanders gradually change shape and move across the floodplain and
migrate downstream.

Question 20

Describe the formation of interlocking spurs

Answer 20

In the upper course of a river most of the erosion is vertically downwards.
This creates steep-sided, V-shaped valleys

The rivers lack the power to erode laterally (sideways), so they have to wind around the high hillsides that stick out into their paths on either side

The hillsides that interlock with each other as the river winds around them are called interlocking spurs

Question 21

State the formations of landforms resulting from erosion and deposition

Answer 21

Meanders and ox-bow lakes

Question 22

Where can meanders be found

Answer 22

In the middle and lower courses

Question 23

Describe how meanders are formed

Answer 23

The current is faster on the outside of the bend because the river channel is deeper and there is less friction (to slow the water down).

Therefore more lateral erosion (through abrasion and hydraulic action) takes place on the outside of the bend, which undercuts the banks forming steep-sided river cliffs

The current is slower on the inside of the bend because the river channel is shallower and there is more friction, (which slows the water down)

Therefore more eroded material gets deposited on the inside of the bend, (because there is more friction), forming slip-off slopes

Over time, because of erosion and deposition,
meanders gradually change shape and move across the floodplain and
migrate downstream.

Question 24

What is a meander

Answer 24

A meander is a bend in the river

Question 25

Explain why a waterfall is only a temporary feature on a river’s course (4 marks)

Answer 25

The river will try to develop a smooth long profile. A waterfall is formed where the river flows over a band of more resistant rock (1).

This represents an irregularity in the river’s long profile that it will try to remove. Where the more resistant rock overlays less resistant rock, different rates of erosion take place as the less resistant rock is eroded faster than the overlying harder rock by abrasion and hydraulic action (1).

Over time the less resistant rock is removed leaving a shelf of more resistant rock overhanging. Eventually this overhang will collapse and the waterfall will retreat further upstream (1).

This process continues until all the more resistant rock has been removed, the waterfall disappears and the river’s long profile is smoothed out, therefore a waterfall is only a temporary feature (1).

Question 26

Describe how ox-bow lakes are formed

Answer 26

Ox-bow lakes are formed from Menaders

Erosion (by abrasion and hydraulic action) causes the outside bends of meanders to get closer until there is only a small bit of land between the bends (called the neck)

The river breaks through this land, usually during a flood and the river flows along the shortest course

Deposition eventually cuts off the meander forming an oxbow-lake.

Question 27

Examples of formations of landforms resulting from deposition

Answer 27

levées, flood plains
and estuaries.

Question 28

Describe how flood plains are formed

Answer 28

The flood plain is the wide valley floor on either side of a river which ocassionally floods

When rivers flood, the water slows down, loses energy and deposits the material that its transporting. This builds up the flood plain

Meanders widen as they migrate (move) across floodplains laterally,
Over time, meanders also migrate downstream.

The deposition that happens on the slip-off slopes of meanders also builds up the flood plain

Question 29

Describe how levees are fromed

Answer 29

Levees are natural embankments (raised banks) along the edges of a river channel

During flood, eroded material is deposited over the whole flood plain

The heaviest material is deposited closest to the river channel, because it is dropped first when the river slows down and loses energy

Over time, the deposited material builds up, creating levees along the channel

Question 30

Describe how Estuaries are formed

Answer 30

Estuaries are found at river mouths.
The land is close to sea level and the river valley is at its widest.

The water here is tidal - the river level rises and falls each day

When the water floods over the banks of the river, it carries silt and sand onto the valley floor

As the tide reaches its highest point, the water moves slowly and has little energy, so it deposits sediments

Over time, more mud builds up, creating large mudflats

At low tide, the wide, muddy banks are exposed

Question 31

A levee could become a ______

Answer 31

A levee could become a floodplain