Rivers

Question 1

Where is the source of a river often located?

Answer 1

In upland areas

Question 2

Where is the mouth of the river often located?

Answer 2

In lowland areas usually at the coast

Question 3

What does the upper course of a river have?

Answer 3

• Larger bed load of material
• Vertical erosion due to upland area
• Waterfalls
• White water
• High amount of friction

Question 4

What does the middle course of a river have?

Answer 4

• Bed load and material is starting to decrease
• Lateral erosion meaning a widerR channel
• Meanders and oxbow lakes
• Less steep
• High velocity

Question 5

What does the lower course of a river have?

Answer 5

• Largest cross-section but lots of material deposited meaning a narrower channel
• Deposition
• Large discharge but slower velocity

Question 6

What are the four main types of erosion and how do they work?

Answer 6

• Hydraulic Action-The force of the water traps air in the cracks in the bank which gradually causes it to wear away
• Abrasion-Rocks carried by the river wear down the banks
• Attrition-Rocks being carried by the river smash together into smaller particles
• Solution-Soluble particles are dissolved

Question 7

What are the four main types of transportation and how do they work?

Answer 7

• Solution-Soluble particles are carried dissolved
• Saltation-Small pebbles and stones bounced along the river bed
• Suspension-Fine and light materials carried by the water
• Traction-Large boulders are rolled along the river bed

Question 8

What are the three types of weathering and how do they work?

Answer 8

• Freeze thaw-Where water gets into the cracks then freezes.Repeatedly expanding until the material breaks away
• Chemical-Rain etc
• Biological-Tree roots and animal burrows destabilising banks

Question 9

Where does deposition happen and why?

Answer 9

• At the mouth or during floods

- The area is flatter and therefore the river has less energy to carry material

Question 10

What can deposition form?

Answer 10

-Deltas

Question 11

What landform is formed in the upper course?

Answer 11

Waterfalls

Question 12

How do waterfalls form?

Answer 12

• A band of hardrock is on top of a band of softrock on a ledge.
• The river flows over the hard rock and into the area below
• Through abrasion and hydraulic action the soft rock underneath erodes leaving an overhang
• The area directly below where the water falls is eroded by swirling debris creating a plunge pool
• Eventually, the overhang becomes unstable and collapses.
• The waterfall retreats

Question 13

What landforms are formed in the middle course?

Answer 13

-Meanders and ox bow lakes

Question 14

How is an ox bow lake formed?

Answer 14

• Due to lateral erosion rivers have one fast moving current called the Thelweg and one slower moving side.
• The faster side erodes the bank causing it to go outwards and the slower side deposits material causing it to retreat slightly creating a meander
• As the meander becomes more extreme the ends get closer together so when the river floods material gets deposited and the river takes a new faster course cutting off the loop.
• The river is now straight and the ox bow lake is completely seperate

Question 15

What landform is formed in the lower course?

Answer 15

-Deltas

Question 16

How does a Delta form?

Answer 16

• As the river reaches the mouth more material is deposited
• This creates a mound of material spilling into the sea
• As the river wants to get to the sea as quickly as possible distributaries are formed where water makes smaller tributaries through the deposition

Question 17

What human factors negatively affect flooding?

Answer 17

• Tarmac and non-permeable surfaces increase water runoff so water does not get absorbed
• Deforestation-Trees absorb water so reducing the number of trees means more water is going to run off banks into rivers
• Building on floodplains-Self explanatory

Question 18

What physical factors affect flooding?

Answer 18

• Heavy rainfall or just long periods of rain increased water reaching rivers quicker.
• Snow melt ^
• Steep slopes (e.g valleys) as water reaches river without much absorbtion
• Impermeable rock increased water run off as water cannot be absorbed
• Saturated or very dry soils increased water run off as rain can not be absorbed

Question 19

What is it called when plants stop water from running into rivers?

Answer 19

-Interception

Question 20

What is the time between the peak rainfall and peak discharge called on a hydrograph?

Answer 20

-The lag time

Question 21

What does a short lagtime on a hydrograph mean?

Answer 21

-A flash flood

Question 22

What would the falling limb on a hydrograph look like if there was a flash flood?

Answer 22

-Steep

Question 23

What is the baseflow on a hydrograph?

Answer 23

-The rivers usual level of discharge

Question 24

What factors influence lagtime

Answer 24

• Size of drainage basin
• Vegetation
• Valley steepness
• Soil type

Question 25

What is hard and soft engineering when it comes to rivers?

Answer 25

• Hard-Building artificial structures (usually more expensive)
• Soft- More natural approaches that don’t require construction

Question 26

Name two types of Hard Engineering flood management and their pros/cons

Answer 26

• Dams and reservoirs:
  
  • Pros-Can produce electricity, Attract tourists
  • Cons-Habitats flooded, people forcibly relocated, Expensive
• River straightening and dredging:
  
  • Pros-More water can be held in the channel, reduces flood risk in built-up areas
  • Cons-Dredging needs to be done frequently, Increases flood risks downstream

Question 27

Name two types of Soft Engineering flood management and their pros/cons

Answer 27

• Flood warnings:
  
  • Pros-People have time to protect themselves, Possessions can be saved
  • Cons-Flash floods may happen too quickly, doesn’t prevent floods only warns people
• Floodplain zoning:
  
  • Pros-More expensive buildings and land use are further away causing less damage,
  • Cons-Land changes arent always possible