1.3 River Channel processes and Landforms

Question 1

What is abrasion?

Answer 1

Waters throw sand, shingle and cobbles at the landscape to erode banks. aka Corrasion

Question 2

What is Solution (erosion) ?

Answer 2

Chemicals is the water dissolve rocks such as chalk and limestone. aka Corrosion

Question 3

What is Hydraulic action?

Answer 3

Erosion produced by the energy and power of the water as it hits banks and landscape. Pressure create by water forced into cracks.

Question 4

What is attrition?

Answer 4

Erosion where particles bang together so they become smaller and more rounded.

Question 5

What is traction?

Answer 5

Movement of large boulders and stones as they roll along the river bed

Question 6

What is saltation?

Answer 6

Small rocks bounce along the river bed

Question 7

What is suspension?

Answer 7

Very small particles of sand and silt carried in the flow

Question 8

What is solution (transport) ?

Answer 8

Dissolved minerals from rocks within water move with water

Question 9

What is the Hjulstrom Curve?

Answer 9

A graph used by hydrologists and geologists to determine whether a river will erode, transport, or deposit sediment.

Question 10

What is velocity?

Answer 10

The speed in a direction.

Question 11

What is discharge?

Answer 11

The amount of water flowing down a river at any one time. Discharge is measured in cubic meters of water per second (cumecs)

Question 12

What is laminar flow?

Answer 12

The horizontal movement of water downwards, over a smooth surface, in a simple sheet, with no eddies or meanders. Very rare but most common in lower course of river and straight channels.

Question 13

What is turbulent flow?

Answer 13

Occur in complex, winding channels where water flowing in a river is subject to friction, both with the bed and the banks. This leads to chaotic flow and a series of erratic ‘eddies’ which are both horizontal and vertical.

Question 14

What is helicoidal flow?

Answer 14

The line of fastest flow in a river channel follows a corkscrew or spiralling path as the river moves downstream. Occurs in meanders and is responsible for alternating erosion and deposition in meanders.

Question 15

Why are straight river channels rare?

Answer 15

Helicoidal flow dominates in most rivers and makes them meander.

Question 16

Where are the most pronounced meanders found?

Answer 16

Floodplains where lateral erosion occurs due to soft nature of river banks. Rivers mainly meander due to helicoidal flow.

Question 17

What are braided river channels?

Answer 17

Channels that contain a large number of islands and bars made of sediment. Braiding results from deposition of sediment in river bed during a time of falling discharge. River splits as it flows around these deposits

Question 18

What is a river cliff?

Answer 18

The steep outer bank of a river meander.

Question 19

What is a point bar?

Answer 19

The material deposited on the gentle inner bank of a river meander.

Question 20

What is an oxbow lake?

Answer 20

An old meander which has become cut off from the river. Often filled with marshy vegetation.

Question 21

What are riffles?

Answer 21

Areas of shallow water along the course of a river, often spaced regularly between deeper areas known as pools.

Question 22

What is a gorge?

Answer 22

A deep, steep-sided valley.

Question 23

What is a bluff?

Answer 23

A low hill at the side of a flood plain.

Question 24

What is a floodplain?

Answer 24

Flat land next to a river which is liable to flood when river rises after heavy rainfall. Often badly drained with marshes and oxbow lakes.

Question 25

What are levees?

Answer 25

Raised banks on either sides of a river flowing across a flood plain. Might cause the river to flow above the level of flood plain.

Question 26

What is a delta?

Answer 26

An area of flat land (formed by river deposits) where a river meets the sea or a lake.

Question 27

What is sinuosity?

Answer 27

The sinuosity of a river channel is a measure of how bendy it is. It is calculated by dividing the length of the river channel by the length of the valley in which it flows.

Question 28

What is an alluvial fan?

Answer 28

A fan of sand and gravel deposited by short-lived torrents at the foot of mountains. Not restricted to arid climates, although they are characteristic features of them.

Question 29

What are potholes?

Answer 29

Potholes are cylindrical holes in the bed of a river that vary in depth and diameter from a few centimetres to several metres. They’re found in the upper course of a river where there’s more energy. When flowing water encounters bedload, it is forced over it and downcuts behind the bedload in swirling eddie currents. These currents erode the river’s bed and create small depressions in it. As a result of the eddie currents, the pebbles drill into the depressions making them more circular, wider & deeper.

Question 30

What are rapids?

Answer 30

Rapids are areas of shallow, fast-flowing water in a stream.