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GCSE Geography > River Processes > Flashcards

River Processes Flashcards

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1
Q

Describe the drainage basin hydrological cycle (imputs,flows/stores, outputs)

A

-IMPUTS:
- Precipitation
FLOWS/ STORES:
Stores:
- Interception
- Surface storage
- soil moisture
- ground water storage
Flows:
- throughflow
- Groundwater flow
- Surface runoff
- river runoff
- Infiltration
-percolation

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2
Q

What is the definition for a source?

A

The area in which a river begins

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3
Q

What is the definition for a mouth?

A

Where a river ends it’s journey, flowing into the sea or a lake

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4
Q

What is the definition for a tributary?

A

A smaller river which joins a larger river

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5
Q

What is the definition for a confluence?

A

The point at which two rivers join

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6
Q

What is the definition for a watershed?

A

The boundary between two drainage basins marked by a ridge of high land

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7
Q

What is the definition for a drainage basin?

A

The area which is drained by a river and it’s tributaries

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8
Q

What is the definition for drainage density?

A

The total length in all the stream in the basin divided by the total area of the basin

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9
Q

What are the different processes of river erosion?

A

Attrition, Abrasion, Solution, Hydraulic action

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10
Q

What is attrition?

A

The rocks and pebbles being carried by the river crash against each other, knocking off their sharp corners, so they become smaller and more rounded

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11
Q

What is abrasion?

A

Material that is carried by the river is thrown and rolled against the bed and the banks with sufficient force to wear the banks away (sand papering action)

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12
Q

What is solution?

A

The chemical erosion of the rocks along the riverbank by the slightly acidic water. This occurs in streams running through rocks such as chalk and limestone.

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13
Q

What is hydraulic action?

A

The water forces water into cracks and so air becomes trapped and puts pressure into the rock on the river bank. This constant pressure causes the rocks to eventually crack and break apart.

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14
Q

Draw and label a diagram of a river basin

A

Include:

  • mouth
  • watershed
  • tributary
  • confluences
  • sea/lake
  • source
  • drainage basin
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15
Q

what are the different ways a river transports material

A

traction, saltation, suspension, solution

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16
Q

what is traction

A

boulders and pebbles are rolled along the river bed at times of high discharge and velocity

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17
Q

what is saltation

A

sand sized particles are bounced along the river bed by the flow of water

18
Q

what is suspension

A

fine clay and sand particles are carries along within the water, even at low discharges

19
Q

what is solution

A

some minerals dissolve in water, such as calcium carbonate. this requires very little energy

20
Q

what is deposition

A

when the speed of moving water decreases it will lose energy and no longer be able to carry out so much erosion and transport. particles will be dropped off in order of decreasing size

21
Q

what river landforms and processes occur in the upper course of the river

A
  • river EROSION (attrition, hydraulic action, abrasion, solution)
  • river landforms - upstream - Vshaped valleys, waterfalls, interlocking spurs
22
Q

what river landforms and processes occur in the middle course of the river

A
  • river TRANSPORTATION (traction, saltation,suspension, solution)
  • river landforms - meanders, meander migration, oxbow lakes
23
Q

what river landforms and processes occur in the lower course of the river

A
  • river DEPOSITION
  • river landforms- near the mouth of the river- levees, deltas, floodplains
24
Q

how are v shaped valleys formed

A
  • the river erodes downwards as boulders, stones and rock particles are bounced and scraped along the channel bed
  • as the river cuts down, the steep sides are attacked by weathering. this breaks up and loosens the soil and rock.
  • the loosened material slowly keeps down the slope because of gravity or is washed into the river by rainwater. The river carries it away.
  • the end result is a deep sided valley which has the shape of the letter V
25
Q

how are waterfalls/ gorges formed?

A
  • a river falls over a hard rock edge, meeting a band of softer, less resistant rock at the bottom.
  • processes of erosion, mainly abrasion and hydraulic action, cause undercutting. the underlying, soft rock is eroded more quickly
  • the more resistant rock is left unsupported and overhangs. Hydraulic action causes a plunge pool under this rocket form
  • eventually the more resistant rock collapses onto the river bed
  • a steep sided river valley is created called a gorge. this process is repeated and the river/ waterfall retreats upstream
26
Q

label a diagram of how a meander is formed

A

include:
- slowest flow
- fastest flow
- beach
- deposition of sand on inside bend
- shallow water
- deep water
- bank worn away
- erosion on outside bend causing undercutting
- flow
- river cliff

27
Q

how are meanders formed

A
  • a river rarely flows in a straight line, it will bend around something in its course, e.g a tree or hard rock
  • this results in areas of slower and faster water movement
  • the river flows faster on the outside, because this is where water is pushed (more water= more energy = faster flow) and erodes these outside bends by processes such as hydraulic action and abrasion, forming a river cliff
  • the river flows more slowly on the inside bend of a river channel and deposits some of its load, creating river beach
  • continuous erosion on the outer bank and deposition on the inside of a river creates a meander in the river
  • over time, meanders become larger and more recognisable
28
Q

how are ox bow lakes formed

A
  • in meander, the water is pushed to the outside bend, so processes such as abrasion will cause lateral erosion
  • continual erosion on the outside bend narrows the meander neck (neck of land)
  • the river floods, and takes the shortest route, cutting through the neck
  • the fastest current is now in the centre of the channel
  • deposition occurs along the banks of the river, eventually making the meander cut off, leaving an ox bow lake
  • the ox bow lake will slowly dry up, unless rainfall is very high
29
Q

how do deltas form?

A
  • deltas are located at the mouth of a river as it enters a sea or lake
  • on reaching the sea, it suffers a loss of energy as its velocity decreases and so deposition occurs
  • sea water is denser and salty, which helps the sand particles to bind together, becoming heavier and sinking to the sea bed
  • sometimes deposition occurs in the main channel and blocks it. the river then has to divide into a series of smaller channels called distributaries in order to reach the sea
  • over time deposition of silt occurs in and on the banks of the distributaries to form islands and levees
  • as a river approaches the sea it has the energy to carry huge amounts of sediment as suspension
  • eventually the delta grows both upwards and outwards into the sea to form new land often colonised by vegetation. the growth of this vegetation raises it above sea level.
30
Q

what conditions are needed for a delta to form

A
  • the sediment load in the river must be substantial (due to active erosion in the upper course)
  • needs to be a sheltered sea/ lake where there are no strong tides or currents
  • the supply of sediment must be greater than the rate at which tides or currents are able to remove it from the mouth of the river
31
Q

how are levees formed

A
  • Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.
  • Sediment that has been eroded further upstream is transported downstream.
  • When the river floods, the sediment spreads out across the floodplain.
  • When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away.
  • After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water (a greater discharge) and flooding is less likely to occur in the future (natural embankments)
32
Q

what is a floodplain made out of

A

silt, sometimes alluvium (good for farming as is fertile)

33
Q

what are the natural causes of flooding in Bangladesh

A
  • very low lying (70% of its land area is less than 1m above sea level and 80% is floodplain)
  • receives large amounts of water passing through it - three major rivers (the Ganges, Meghna and Brahmaputra), with the Ganges and Brahmaputra converging and forming a huge delta
  • has a monsoon climate and the annual torrential rains from June to September often cause rivers from exceeding their capacity and flooding.
  • in the spring, melting snow from the Himalayas increases flood risks as torrents of melting snow enter the rivers at their source
  • the ground is baked hard before the monsoon season, making it impermeable, meaning there is more surface runoff
34
Q

what are the human causes of flooding in Bangladesh

A
  • intense deforestation in the Himalayas has led to less trees and therefore more soil erosion. this means less interception and more water and silt in the river
  • Bangladesh is an LEDC and its lack of money and heavy national debt means that little money is available to spend on flood protection and many existing defences lack upkeep and are of questionable use
  • population growth, leading to increased population density and more urbanisation, which reduces infiltration and increases surface runoff
  • poor transport and communication skills means there is not good warning or evacuation due to lack weather warnings
  • global warming means that more snow on the Himalayas melts
35
Q

what were the short term effects of flooding on Bangladesh?

A
  • 50% of country flooded
  • 7 million homes destroyed
  • 30 million people were homeless
  • wells were polluted (clean water contaminated and as a result 100,000 people suffered from water Bourne diseases)
  • 750 people died
36
Q

what were the long term effects of flooding on Bangladesh?

A
  • people had no electricity for weeks
  • 1 million people were forced to live in temporary accommodation
  • crop were ruined, leading to food shortages
  • total damage accounted to 7 billion dollars
37
Q

how did Bangladesh respond to the flooding in the short term

A
  • boats to rescue people
  • emergency supplies for food, water, tents and medicines
  • fodder for livestock
  • repair and rebuild houses, as well as services such as sewage etc.
  • aid from other countries
38
Q

how did Bangladesh respond to flooding in the long term

A
  • reduced deforestation in the Himalayas
  • built 7 large dams in Bangladesh to store excess water, costing 30-40 million dollars + 40 years to complete
  • built flood shelters to accommodate the population
  • built 350km of embankment- to reduce flooding along the main river channels
  • developed an effective flood warning scheme
39
Q

what make rivers less likely to flood

A
  • slow drizzle all day
  • soil that is dry before the rain storm
  • chalk (a porous rock which stores water)
  • woodland and trees in the drainage basin
  • gentle slopes that water flows off slowly
  • the countryside, with fields full of crops
40
Q

what makes rivers more likely to flood

A
  • heavy rainfall for several hours
  • soil that is saturated (soaked) before the rainstorm
  • granite (an impermeable rock which doesn’t store water)
  • very few plants in the drainage basin
  • steep slopes which drain quickly
  • a built up area with many tarmac surfaces

GCSE Geography (7 decks)

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