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GCSE Geography > Physical Landscapes - Rivers > Flashcards

Physical Landscapes - Rivers Flashcards

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1
Q

Landscape

A

An area whose character is the result of the action and interaction between natural and human factors

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2
Q

Watershed

A

Edge of river basin

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3
Q

Source

A

Start of the river

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4
Q

Tributary

A

Small stream that joins larger river

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5
Q

Confluence

A

Where a tributary joins a larger river

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6
Q

Mouth

A

End of a river, where it joins the sea

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7
Q

Drainage basin

A

Area of land drained by a river or its tributaries

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8
Q

Features of upper course

A

Vertical erosion due to gravity
Narrow stream
Most confluences are found here
Interlocking spurs/waterfalls

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9
Q

Features of middle course

A

Vertical + lateral erosion; less steep
Wider stream than upper course
Meanders + oxbow lakes
Sediment in river enlarges meanders

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10
Q

Features of lower course

A 
Lateral erosion
Wide stream - fast moving/powerful current
Mouth of a river found here
Estuaries, floodplains and levees
Lots of deposition
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11
Q

Vertical erosion

Lateral erosion

A

Downwards erosion

Sideways erosion

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12
Q

Hydraulic action

A

Force of water erodes river bed

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13
Q

Abrasion/corrosion

A

Bed and banks worn down by river’s load

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14
Q

Attrition

A

Eroded material carried by river bumps into each other - smoothed/broken down even smaller

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15
Q

Solution

A

Chemical erosion (dissolving) of river bed and banks

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16
Q

Traction

A

Material rolled along river bed

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17
Q

Saltation

A

Small particles bounce along river bed (leap-frog action)

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18
Q

Suspension

A

Small particles (silt and clay-sized) carried in river’s turbulent flow

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19
Q

Solution

A

Dissolved minerals carried in river solution

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20
Q

When does deposition occur?

A

Velocity of river decreases
Not enough energy to transport materials
Larger rocks deposited in upper course - only transported for small distances by traction
During periods of very high flow
Finer sediment carried downstream - suspension/solution
Deposited on river bed/banks when river is slowed by friction
Large amount of deposition occurs at river mouth
River’s velocity greatly reduced during interaction with tides with gentle gradient

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21
Q

Interlocking spurs

A

Outcrops of land along river course in a valley

River doesn’t have enough power to cut through harder rock near its mouth, so it flows around them

22
Q

Gorge

A

Narrow steep-sided valley found immediately downstream of a waterfall
Gradual retreat of waterfall over hundreds/thousands of years
Can form collapse of underground caverns or melting glaciers (e.g. end of the last glacial period)

23
Q

Waterfalls

A

Water falling from a height over a steep rock face
Water erodes soft rock quicker than hard rock, forming steps
When water plunges over these steps, it creates a plunge pool - abrasion and hydraulic action undercut the waterfall
Eventually, overhang collapses and waterfall retreats
This will eventually leave a steep-sided gorge
Waterfalls can also be found in glacial hanging valleys

24
Q

Meander

A

Wide bends in a river, mainly found in lowland areas
Shape and position are constantly changed by lateral erosion and deposition
Thalweg - fastest line of flow, swings from side to side causing erosion on the outside bend and deposition on the inside bend.
This causes meanders to migrate across valley floor

25
Q

Pool

A

Deeper, slow-moving section of a river
Finer deposits due to low velocity
Form close to the outside bend where lots of erosion takes place, making a deeper section - usually in the path of the thalweg

26
Q

Riffle

A

Shallow, fast-moving section of a river
Faster flowing - may have deposits of coarser gravel
Form between meander bends - decreased velocity causes more deposition of coarser sediment, and a shallower river channel

27
Q

Oxbow lakes

A

Meander becomes bigger and bigger, eventually having a very narrow neck
Period of extreme discharge cuts off the neck, creating a straighter channel
Deposition at river sides will block off the old meander

28
Q

Floodplain

A

Wide, flat area of marshy land either side of a river
Mainly made of alluvium (sediment that has been deposited from river) - very fertile, good for farming
Meanders migrate across floodplain due to lateral erosion - erode the valley side when they reach edge of floodplain. This is why floodplains are wide

29
Q

Levee

A

Raised river bed found alongside a river in its lower course
Formed by flooding over many years - deposited sediment builds up
Act almost like a natural flood defence system

30
Q

Estuary

A

Transitional zone between river and coastal environments
Affected by wave action as well as fluvial processes
Rising tide - river water unlikely to be able to be discharged into the sea. Velocity falls - lots of deposition takes place, forming mudflats at low tide

31
Q

High Force Waterfall and Gorge

A

Located close to Forest-in-Teesdale, upper course of the river
20m drop - continues through gorge
Hard band of igneous rock - dolerite
Underlying, soft limestone - easily eroded
Example of basic waterfall formation

32
Q

Flooding

A

Where land becomes inundated (overwhelmed) by water
River channel cannot hold the amount of water flowing through it
Water breeches banks and floods the floodplain
Usually occur after long period of rainfall (e.g. winter) as volume gradually increases, until channel can no longer cope

33
Q

Flash flood

A

Sudden flood after a torrential storm

34
Q

Factors affecting flood risk

A

Vegetation cover - intercepts and slows rainfall
Climate - distribution of rainfall throughout year + temperature
Slopes - steep/gentle/curved shape affects speed of water
Rainfall intensity/duration - intense rain will increase overland flow and lag times, gentle rain over long time allows more infiltration (ground flow and throughflow)
Land use - impermeable surfaces from urbanisation (e.g. tarmac) increase overland flow, different crops affect interception e.g. cereals 7-15%
Soil type and depth - affects how quickly water can infiltrate and become ground/through flow, and how much water can infiltrate the soil
Lakes and reservoirs - store rainwater, prevent it overwhelming river channel, prevents floods
Rock type - impermeable rocks prevent ground flow, encourage throughflow and overland flow, decreases lag time

35
Q

Hydrograph

A

Graph that plots river discharge after a storm

Shows how discharge rises after a storm, reaches its peak and returns to normal flow

36
Q

Time lag

A

Time (hours) between highest rainfall and highest discharge
Shows how quickly water is transferred into river channel - key factor in flood risk
Short lag time - increased risk of flooding

37
Q

Costs

A

Financial cost of a scheme, negative impact on environment and people’s lives

38
Q

Benefits

A

Financial savings by preventing flooding and environmental improvements

39
Q

Dam building

A

Holds water back behind dam in a reservoir
+ hydroelectric power generation
- expensive
- settlements lost when reservoir created
- sediment trapped behind dam causes erosion downstream

40
Q

River engineering

A

Widening or deepening the river channel
+ allows river channel to carry more water
+ can be diverted away from settlements
- water carried faster, reduces lag times

41
Q

Dam building - case study

A

Clywedog, Wales
Constructed in 1960s to prevent flooding of River Severn
70m high, 230m wide
Stretches for 10km
Fills up in winter, gradually released in summer - constant flow
Some flooding still occurs downstream

42
Q

Channel straightening

A

Cutting through meanders to create a straight channel - some sections filled with concrete
+ water flow sped up
+ protects vulnerable areas from flooding
+ concrete prevents banks from collapsing
- increase flood risk downstream
- just shifts problem elsewhere
- very unattractive
- may damage wildlife habitats

43
Q

Embankments

A

Raised river bank
+ river channel can hold more water before flooding occurs
+ protects expensive property
+ relatively cheap and sustainable (low maintenance)
- can be unattractive or out of place
- often not built high enough

44
Q

Flood relief channels

A

Man-made river channel constructed to bypass an urban area
+ flood water diverted during periods of high flow
- expensive
- uses a lot of land

45
Q

Floodplain zoning

A

Policies to control urban development close to/on the floodplain
+ cheap way to reduce risk to property
+ sustainable
+ surface runoff less likely to cause flooding as floodplain has not been built on
- resistance due to housing shortages
- enforcement can be more difficult in LICs

46
Q

Washlands

A

River is allowed to flood naturally in wasteland areas, to prevent flooding near settlements or urban areas
+ cost effective
+ potential wetland sites for birds and plants
+ deposited silt enriches soil, agricultural opportunities
- large areas of land taken over, cannot be built on
- productive land turned into marshland

47
Q

Warning systems

A

Sirens, TV, text messages, etc. keep people informed about possible flooding
+ cheap
+ electronic communication is effective
+ opportunity to move valuable possessions to a safer place
- sirens could be vandalised - must be tested annually
- may not be enough time for residents to prepare

48
Q

Afforestation

A

Trees planted in catchment area intercept rainfall and slow water’s flow to the river
+ relatively low cost
+ improves quality of environment
+ soil erosion avoided, as trees prevent rapid runoff after heavy rainfall
+ very sustainable
- conifers can make soil acidic
- dense tree plantations spoil natural look of the landscape
- increased fire risk due to leisure activities in the forest

49
Q

Banbury location and history

A

Cotswold Hills, 50km North of Oxford
Population of 45,000
River Cherwell floodplain (tributary to River Thames)
1998 - devastating flood caused £12.5mn in damage, affecting 150 homes and businesses
2007 - widespread flooding affects many homes and businesses

50
Q

Banbury - new flood defence scheme

A

2012
2.9km earth embankment built parallel to M40 - flood storage area
Embankment has a max. height of 4.5m
Flood storage area located on natural floodplain of River Cherwell

51
Q

Other flood defence measures at Banbury

A

Raising A361 in flood storage area
Improvements to drainage beneath the road
Earth embankments and floodwalls to protect property and businesses
Pumping station to transfer excess rainwater
Biodiversity Action Plan habitat - ponds, trees and hedgerows to absorb and store excess water

GCSE Geography (6 decks)

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