Land and Water, River Processes

Question 1

What two key aspects of rivers are essential to their existence and management?

Answer 1

Diveristy and adaptability. Different rivers adapt differently to different conditions

Question 2

Impelling and resisting forces

Answer 2

Impelling forces: Drive change. Measured by river energy

Resisting forces: Resist change. Measured by flow resistance factors

Question 3

What are the two types of flow?

Answer 3

1. Laminar
2. Turbulent

Question 4

Laminar flow

Answer 4

Water layers slide over each other as thin, coherent layers, thus conserving energy

Question 5

Turbulent flow

Answer 5

Chaotic movement of water with rough bed eddies, thus causing significant energy loss

Question 6

What element is the main driver of gross stream power and unit stream power?

Answer 6

The amount of water because it determines the amount of energy that is distributed throughout the river

Question 7

Describe the three measurements of river energy

Answer 7

1. Gross stream power
2. Unit stream power
3. Mean boundary shear stress

Question 8

Gross stream power

Answer 8

The avalaible energy in a river

Question 9

Unit stream power

Answer 9

The avalaible energy in a river per unit of channel width

Question 10

Mean boundary shear stress

Answer 10

The energy acting on the bed/banks of a river

Question 11

What percentage of a river’s energy is dissipated by friction?

Answer 11

97%. This leaves only 3% for sediment transport

Question 12

Describe the three types of resistance within a river

Answer 12

1. Internal flow resistance
2. Boundary resistance
3. Channel resistance

Question 13

Internal flow resistance

Answer 13

The resistance of a fluid to change shape

Question 14

Boundary resistance

Answer 14

Grain and form roughness

Question 15

Channel resistance

Answer 15

Bank and planform (shape) roughness

Question 16

Thalweg

Answer 16

The highest velocity filament in a river, located away from boundary resistance in the middle of the channel near the surface

Question 17

What are the three types of channel shapes and their roughness?

Answer 17

1. Narrow and deep
2. Wide and shallow
3. Rough streambed

Question 18

What are the two characteristics of narrow and deep channels?

Answer 18

1. Less resistance
2. Faster flow

Question 19

What are the two characteristics of wide and shallow channels?

Answer 19

1. More resistance
2. Slower flow

Question 20

What are the two characteristics of rough streambed channels?

Answer 20

1. Also more resisance
2. Also slower flow

Question 21

Lane balance

Answer 21

A balance between sediment size and stream flow, each aggrading and degrading respectively

Question 22

Why is bed stability important?

Answer 22

The bed erodes before the banks; it is the cradle of the river. River management strategies that do not address its stability are likely to fail

Question 23

What does the Hjulström curve indicate about the three types of sediment?

Answer 23

1. Fine: Difficult to transport because sticky
2. Sand: Easy to transport because light and not sticky
3. Coarse: Difficult because heavy

In conclusion, rivers love sand

Question 24

What are the three ways that sediment is transported throughout a river?

Answer 24

1. Saltation/punctuated movement
2. Suspension
3. Solution

Question 25

What are the two causes of sediment deposition?

Answer 25

1. Velocity decreases 2. Excessive load Coarsest particles tend to be deposited first

Question 26

What causes bank erosion

Answer 26

A combination of hydraulic action and abrasion which leads to mass failure of the channel banks

Question 27

What two types of accretion cause floodplain formation?

Answer 27

1. Lateral accretion 2. Vertical accretion

Question 28

Lateral accretion

Answer 28

Sediment is deposited within the channel on the inside of bends to form point bars

Question 29

Vertical accretion

Answer 29

Sediment is deposited over the bank (typically occurs during floods)