The Long Profile and Channel Characteristics

Question 1

What is base level?

Answer 1

The lowest point that the river can erode to

Question 2

Total erosion and deposition along the full course of a river are balanced, why may there still be an uneven profile?

Answer 2

Rates of erosion and deposition change along the course, results in formations like waterfalls

Question 3

What are the 3 stages of a river?

Answer 3

Upper course
Middle course
Lower course

Question 4

Characteristics of the upper course

Answer 4

Gradient is steep
River is high above sea level
Lots of potential energy

Question 5

Characteristics of the middle course

Answer 5

Gradient decreases
Potential energy is converted into kinetic energy
River gains velocity

Question 6

Characteristics of the lower course

Answer 6

River has little potential energy
Lots of kinetic energy
Flows faster - greater velocity

Question 7

What do channel characteristics affect?

Answer 7

Velocity and discharge

Question 8

Do velocity and discharge, increase or decrease downstream?

Answer 8

Increase

Question 9

Why does discharge increase downstream?

Answer 9

Tributaries join the river and there is more surface runoff

Question 10

Why does velocity increase downstream?

Answer 10

It’s influenced by gradient, discharge and channel characteristics

Question 11

What is kinetic energy used for?

Answer 11

To overcome friction and causes erosion

Question 12

How does the energy a river has effect efficiency?

Answer 12

More energy a river has for erosion and transportation, more efficient it is

Question 13

What does an efficient river have?

Answer 13

High velocity
High discharge
Little friction

Question 14

How is efficiency measured?

Answer 14

By hydraulic radius

Larger hydraulic radius, more efficient river

Question 15

How do you calculate the hydraulic radius?

Answer 15

Wetted perimeter

Question 16

What channels are more efficient?

Answer 16

Smooth, narrow and deep channels - have larger hydraulic radius’

Larger hydraulic radius means a smaller proportion of water in contact with wetted perimeter, friction is lower, less energy loss, increased velocity and discharge

Question 17

What channels are less efficient?

Answer 17

Shallow and broader ones

Question 18

How does channel roughness effect efficiency?

Answer 18

Protruding banks and large, angular boulders increase wetted perimeter which causes more friction.

Reduces efficiency, velocity and discharge

Question 19

Where is channel roughness greatest?

Answer 19

Upper course

Question 20

Why does channel roughness increasing mean that turbulent flow increases?

Answer 20

Turbulent flow is more effective at picking up particles from the river bed than smooth flow - causes greater erosion.

Question 21

What does a long profile show?

Answer 21

The river’s gradient from its source to the sea

How the gradient of the river channel changes from the rivers source to its mouth by showing the height of the river bed

Question 22

What is erosion like in the upper course?

Answer 22

Manly vertical, by abrasion and a bit of hydraulic action

Occurs in high energy conditions

Rough channel, cause turbulence, large bed load is dragged along river, intense downward erosion

Question 23

What is transportation like in the upper course?

Answer 23

Mainly large particles (boulders) carried by traction or saltation during high energy conditions

Question 24

What is deposition like in the upper course?

Answer 24

Little deposition, mainly largest particles deposited in the river bed as energy levels drop

Question 25

What is erosion like in the middle course?

Answer 25

Mainly lateral and by abrasion

Sediment size decreases at this state through attrition of the larger particles

Question 26

What is transportation like in the middle course?

Answer 26

More material carried by suspension as particle size decreases

Some larger particles moved by saltation

Question 27

What is deposition like in the middle course?

Answer 27

Sand and gravel are deposited across the flood plain as the river floods and friction reduces

Question 28

What is erosion like in the lower course?

Answer 28

Although discharge and velocity are high, erosion is less as turbulence is lower and sediment size is reduced

Some lateral erosion occurs during formation of meanders

Question 29

What is transportation like in the lower course?

Answer 29

Mainly smaller particles (silt and clay) carried by suspension, or substances carried by solution

Question 30

What is deposition like in the lower course?

Answer 30

Smaller particles (silt, clay and sand) are deposited on the flood plain when floods and in river mouth as sea absorbs rivers energy

Question 31

What does a cross profile show?

Answer 31

Shows what a cross section of the river channel or valley looks like

Question 32

What are the characteristics of the upper course in terms of its cross profile?

Answer 32

Valleys are steep v shapes

Vertical erosion creates narrow valley floors and steeply sloped sides

Question 33

What are the characteristics of the middle course in terms of its cross profile?

Answer 33

Valleys are wider caused by lateral erosion

Deposition creates a floodplain on valley floor

Question 34

What are the characteristics of the lower course in terms of its cross profile?

Answer 34

Valley is wide with gently sloping sides

Much wider floodplain caused by deposition