Theme 2b Rivers

Question 1

How river transports materials ?

Answer 1

1. Traction - rolling stones along the bed
2. Saltation - sand-sized particles bounce along the bed in a leapfrog motion
3. Suspension - silt and clay-sized are carried within the water flow
4. Solution - Minerals dissolve in the water

Question 2

Brief description of a drainage basin (can apply this system to a hydrological cycle)

Answer 2

• Drainage basins act as a system with inputs, (precipitation)
• Transfers (inflitration, percolation, surface run-off, throughflow, groundwater flows)
• Stores (interception, surface storage, soil moisture storage, groundwater storage)
• Outputs (evaporation, transpiration, evapotranspiration)

Question 3

What are the 4 types of erosion by river

Answer 3

1. Attrition - large particles such as boulders collide and break into smaller pieces (upper course)
2. Hydraulic action - the sheer force of the river dislodges particles from its banks and bed
3. Corrasion/abrasion - smaller particles rub against the river banks and bed like sand-paper (lower course)
4. Corrosion - acids in the river dissolve rocks (occur at any part of the river)

Question 4

What are the river landforms ?

Answer 4

1. V-shaped valleys
2. Interlocking spurs
3. Waterfalls
4. Rapids
5. Potholes
6. Meanders
7. Ox-bow lakes
8. Delta
9. Flood plain
10. Levées

Question 5

Describe the formation of V-shaped valleys

Answer 5

• In the upper course of the river, vertical erosion is dominant
  => River erodes downwards deepens the river channel leaving the sides exposed
• Weathering & mass movement => material from valley sides collapse into the river forming v-shaped valley

Question 6

Describe the formation of interlocking spurs

Answer 6

• In the upper valley, a river is in the mountains
• Water takes the easiest path downhill => twists and turns around the high land (spurs)
  => forming interlocking spurs

Question 7

Describe the formation of waterfalls

Answer 7

• Form where there is a layer of hard rock with softer rock underneath & water descends vertically
• As water descends, the softer rock is getting eroded much quicker by hydraulic action => forms an undercutting, undercut the hard rock & create a plunge pool
• Continued undercutting creates an overhang which eventually becomes to heavy & collapses into plunge pool
• Repeated collapses => waterfall retreats upstream creating steep-sided gorge on both sides

Question 8

Describe the formation of rapids

Answer 8

• These are areas of rough water (white water)
• Found in the upper course of the river when you get alternate layers of hard and soft rock
• Soft rock erodes quicker creating an uneven river bed & lead to turbulent flow of water

Question 9

Describe the formation of potholes

Answer 9

• Turbulent flow (circular/swirling movement of water) erodes down into the river bed => creates a small depression
• A grinder/small rock carried by the river is trapped in the depression
• Rotates due to the eddies current above it & erode the hole deeper by abrasion
  => creates a circular depression in river bed (pothole)

Question 10

Describe the formation of meanders

Answer 10

• Found in the middle and lower courses of river where lateral erosion is dominant
• Form when fastest flowing water (thalweg) erodes one side of the river => one bank erode more rapidly than the other form river cliff
• On the opposite side, material is deposited as water is flowing slower form slip-off slope
  => creates a bend in river (meander) & gets larger over time

Question 11

Describe the formation of ox-bow lakes

Answer 11

• With distance downstream, size of meander increases
• Erosion on outside bends eventually lead to the formation of meander neck
• During high flow or floods, the river cuts through the neck & straightens its course
• Flow of water at entry & exit of meander will be slower => deposition
• The cut-off meander is an ox-bow lake

Question 12

Describe the formation of delta

Answer 12

• Form when a large river is carrying a high sediment load
• The river loses energy as it enter a lake or sea (at the mouth of river) & sea is sheltered (has few currents to carry away sediment)
  => silt particles stick together (flocculates) becomes more dense & is deposited
• This deposit builds up above water level & vegetation grow on it to stabilise the land forming a delta

Question 13

Describe the formation of flood plain

Answer 13

• High discharge cause water to overflow the banks
• When the river floods, the water spreads across the flat land
• The sudden increase in friction reduce the water’s velocity & fine silt is deposited across flood plain
• Each time the river floods, it deposits a layer of fine silt increases the height of flood plain

Question 14

Describe the formation of levées

Answer 14

• When a river floods, the coarsest material is deposited on the river banks
• Forming a natural embankment called a levée, increases the size of the river channel

Question 15

Causes of flooding

Answer 15

1. A period of heavy, torrential rain leading to high levels of overland flow as water cannot infiltrate
2. Snow and ice melt
3. No flooding protection
4. Impervious surface (urbanisation) & impermeable rocks so water can’t infiltrate (overland flow)
5. Building bridges which restrict the flow of water
6. Deforestation => no interception & increase surface run-off

Question 16

Soft engineering flood management methods

Answer 16

1. Afforestation - trees are planted in the catchment area => intercept the rainfall & slows down flow of water to river
2. Floodplain zoning - local government create policies to control urban development on or closed to flood plain
3. Washlands - river is allowed to flood naturally in wasteland areas
   => prevent flooding in other areas
4. River restoration - removing hard engineering, restoring the channel back to is natural state => reduces flooding downstream
5. Warning systems - network of warning sirens => give people early warning to possible fllods

Question 17

Hard engineering flood management methods

Answer 17

1. Dams - built to control the rate of discharge, holding back water and released in a controlled way
2. Embankments - man made raised river banks => increasing discharge river can hold
3. Channelisation - widening/deepening the river channel => carry more water or straighten to let water move away quicker
4. Flood relief channels - divert some of the flood away from the main channel
5. Flood walls - vertical barriers, made from concrete => reduces erosion
6. Storage areas/washlands - area close to the river => fill water in river during periods of overflowing

Question 18

What is river width and river depth ?

Answer 18

• River width is the horizontal distance of a river from one bank to another measured across the water’s surface
• River depth is the vertical distance from the water’s surface down to the river bed, usually measured at several points to find a mean

Question 19

What is the velocity and discharge of a river ?

Answer 19

• Velocity is a measure of speed, the speed of the water within the river
• Discharge is the volume of water passing a given point over a set time, measured in cumecs

Question 20

What is a drainage basin ?

Answer 20

The area of land drained by a river and its tributaries

Question 21

What are the features of a drainage basin ?

Answer 21

1. Watershed: the boundary between drainage basins
2. Source: the furthest point from the mouth where the river starts e.g upland lake, spring, glacier
3. Confluence: place where two or more streams/rivers meet
4. Tributary: A stream or river flowing into a larger stream or river
5. Mouth: where river enters the sea/ocean

Question 22

What is a closed and open system and examples for both ?

Answer 22

• A closed system is a system with no inputs or outputs e.g hydrological cycle
• An open system is a system that has both inputs and outputs e.g drainage basin

Question 23

What do evaporation, condensation, transpiration and evapotranspiration mean (in order from top to bottom)

Answer 23

• The change of water from liquid to gas (water vapour) due to heat from the sun
• When water cools and changes from water vapour into liquid (water droplets)
• When plants release water vapour from their leaves
• The combined transfer of water vapour from the Earth’s surface and plants

Question 24

What do precipitation, infiltration and percolation mean (list in order from top to bottom) ?

Answer 24

• The transfer of water from the atmosphere to the Earth’s surface in the form of hail, sleet, snow or rain
• When water moves down from the surface into the soil
• The transfer of water down into rocks and aquifers

Question 25

What do overland flow (surface run-off) , through flow and groundwater flow mean (list in order from top to bottom) ?

Answer 25

- Any water flowing across the Earth's surface - The movement of water through the soil between the groundwater store (water table) and the surface - The flow of water through rocks underground

Question 26

What deposition mean what are the materials deposited along the section of the river ?

Answer 26

When a river does not have enough energy to carry materials, it drops them + Heaviest material deposited first (bedload) + Light materials, gravel, sand and silt are known as alluvium => carried further downstream + Dissolved materials carried out to the sea

Question 27

According to the Bradshaw model, how a river changes along the course (from upstream to downstream)?

Answer 27

1. Discharge increases 2. Occupied channel width increased 3. Channel depth increases 4. Average velocity increases 5. Load quantity increases 6. Load particle size decreases 7. Channel bed roughness decreases 8. Slope angle (gradient) decreases

Question 28

What are the 2 main directions of erosion ?

Answer 28

1. Vertical erosion: dominant in the upper course => increases depth of river & valley as erodes downwards 2. Horizontal erosion: dominant in middle & lower courses => increases width of river & valley as erodes sideways

Question 29

What are the opportunities for people living near rivers ?

Answer 29

1. Silt deposited during flood is often rich in minerals & nutrients => high yield crops 2. Floodplains are flat land => easier to build house & transport network 3. Water can be used to irrigate farmland 4. Leisure & tourism opportunities => increase income to locals 5. Easy to transport goods and people using barges & boats 6. Rivers are a source of food (freshwater animals)

Question 30

What are the hazards presented when living near rivers in terms of flooding and river erosion?

Answer 30

1. Flood waters => increase the spread of water-related diseases as water act as breeding ground for animals spread disease e.g mosquito 2. Deaths & injuries as floodplains are densely populated due to fertile soil 3. Bridges & transport routes are damaged by flood waters 4. Erosion of river banks => loss of farmland 5. Destruction of crops 6. Damaged to houses and buildings e.g hospital, school