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AS Geography > Rivers, Floods And Management > Flashcards

Rivers, Floods And Management Flashcards

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1
Q

Watershed

A

Boundary around drainage basin

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2
Q

Hydrological cycle

A

Closed system

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3
Q

Inputs

A

Where water enters the drainage basin

Precipitation

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4
Q

Processes

A

The ways in which water travels

Stemflow, infiltration, groundwater flow, channel flow, throughflow, percolation, interception

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5
Q

Outputs

A

How water leaves the basin

Runoff, evaporation, transpiration,

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6
Q

Different stores

A

Soil storage, vegetation storage, channel storage, surface storage, groundwater storage

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7
Q

Inputs and outputs in winter and autumn

A

Less than summer due to less sunlight, less heat, less output

Ground water stores recharge in winter due to more rain and less output occurs therefore, groundwater stores fill up.

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8
Q

Spring and Summer inputs and outputs

A

Floods in March as groundwater stores full after winter. Soil moisture surplus, for plants and runoff into streams.

Rivers run dry in August and farmers may need to irrigate crops. Soil moisture deficiency due to hotter weather.

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9
Q

Factors that influence water flows within a drainage basin

A 
Intense rainfall
Shape of land
Vegetation and land use
Conditions in basin
Soil type and depth
Size and shape of river basin
Bedrock
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10
Q

River discharge

A

Amount of water in a river passing a given point at any time

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11
Q

Storm hydrograph

A

Graph showing how river discharge changes as a result of heavy rain

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12
Q

Peak rainfall

A

Time of highest rainfall

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13
Q

Peak discharge

A

Time river reaches highest flow

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14
Q

Lag time

A

Time delay between peak rainfall amount and peak discharge

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15
Q

Rising limb

A

River rising on a graph

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16
Q

Falling limb

A

River levels falling on a graph

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17
Q

Bankful discharge

A

The maximum discharge of a river channel is capable of carrying before flooding

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18
Q

Regime

A

A river patterns flow

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19
Q

Discharge formula

A

Velocity x cross-sectional area

Q= V x A
Measured in m3/s

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20
Q

Features of a drainage basin that would produce hydrographs with a high peak discharge

A 
Small lag time 
Steep valleys
High river discharge
Intense rainfall
Bare ground
Small bankful discharge
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21
Q

The long profile from source to mouth

A

Steep gradient, high elevation, vertical erosion
Lateral erosion, valley widens, lower elevation
Alluvium deposition, low gradient, little elevation, highest discharge and velocity here

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22
Q

Erosion processes

A

Hydraulic action
Attrition
Abrasion
Solution

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23
Q

Where material comes from that forms a rivers load?

A

Endogenic

Exogenic

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24
Q

Transport processes

A

Traction
Saltation
Suspension
Solution

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25
Q

The Hjulström curve

A

1 Fine particles suspended in near still water
2 Velocity needed to transport bigger particles is slightly less than needed to pick up particles
3 larger sand particles less erosion velocity than smaller bits as they’re stuck together and hard to pick up
4 smallest bits similar erosion velocity as boulders
5 large gap between erosion and fall velocity shows small bits need less energy to be transported
6 large particles carried for short time - small gap between ev and fv

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26
Q

Capacity of a river

A

Largest amount of material that can be transported

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27
Q

Competence

A

Size of largest particle that can be transported

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28
Q

When deposition occurs

A

Sudden reduction in gradient
Mountain streams where there is large boulders
Sudden inc in load as tributary brings more load
As river floods on floodplain
River entering sea
Reduction in velocity
Shallow water within channel

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29
Q

Factors that affect the amount, type and character of a river’s load

A

Size of drainage basin - wide gradient, smaller particles
Relief - low, more suspended load
Human activity - dams(more dissolved), deforestation(more load)
Precipitation - intense(more carbonic acid)
Underlying geology - resistant(less water, less load)

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30
Q

Erosion, transportation and deposition in the upper course

A

E- vertical, abrasion
T- boulders move in high discharge, traction
D- coarse material stays

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31
Q

Erosion, transportation and deposition in the middle course

A

E- mainly hydraulic, vertical/lateral
T- smaller size, traction or saltation
D- inside pf meanders, floodplain when floods

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32
Q

Erosion, transportation and deposition in the lower course

A

E- reduced but lateral, some hydraulic, outside of bends
T- sand by traction, fine in suspension
D- fine silts and clays on floodplains, coarser dropped first, levees

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33
Q

If base level changes…

A

Irregularities in long profile:
Waterfalls, rapids
Lengths where gradient reduced locally, lakes

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34
Q

Source to mouth

A

Increase: velocities, discharge, load amount, efficiency

Decrease: roughness, friction, turbulence, load size

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35
Q

Potential and kinetic energy

A

Source: high potential, little discharge so low velocity, very high above sea level

Mouth: high kinetic, down long profile river is bigger and moving quicker.
KE= 1/2mv2

36
Q

Landforms of fluvial erosion and deposition

A 
Potholes
Rapids
Waterfalls
Meanders
Oxbow lakes
Floodplains
Levees
Braiding
Deltas - bird foot and arcuate
37
Q

Landforms of rejuvenation

A

River terraces - paired, unpaired
Incised meanders - entrenched, ingrown
Knickpoints

38
Q

Drainage basin

A

Area of land drained by a river

Open system as have inputs and outputs

39
Q

Potholes formation key terms

A

Hydraulic drilling - pebbles
Cylindrical depressions
In rocky beds with high velocity and turbulent flow
Pebbles rotate in hollow, deepening

40
Q

Rapids formation key terms

A

Changes in geology
Water turbulent and erosive power increases
Soft rock erodes faster
Speeds up flow of water and increases turbulence

41
Q

Waterfalls formation key terms

River Tees

A 
Hard rock on top of soft rock - whinstone, limestone
Hydraulic action, abrasion
Soft rock erodes faster, steep gradient
Plunge pool from power, splashback
Overhang collapses
Plunge pool deepens
42
Q

Meanders formation key terms

River Till

A

River at base flow, thalweg zigzags between bars of sediment on opposing banks.
Pools and riffles form
Thalweg on banks undercutting, slower flow deposition, more bend
River not straight, helicoidal flow
River cliffs exaggerate bend from undercutting
More deposition, point bars

43
Q

Helicoidal flow definition

A

When the river is no longer straight the thalweg downstream swings faster like a corkscrew as well as moving vertically.

44
Q

Meander Migration

A

Occurs laterally downstream
Move as thalweg doesn’t match shape of bend
Zone of greatest erosion is midpoint downstream in meander bend

45
Q

River bluffs

A

Outer part of bend reaches valley sides and erodes them

Eventually meanders migrate downstream and slowly widen the valley floor to form flat floodplain.

46
Q

Ox-bow lakes formation key terms

Mississippi

A 
Hydraulic action and abrasion
Material deposited on inside as point bar deposit
Meander shifts position, narrower neck
Flood breaches neck, new straight path
Meander scar
47
Q

Flood plains formation key terms

River Till

A

Discharge increases, wider channels needed
Meanders migrate, widen valley floor
Floods, alluvium deposited
Floodwaters shallow and wide, extensive wetted perimeter, more frictional contact, lower velocities, deposition
Layers of sediment, inc fertility and height of land

48
Q

Levees formation key terms

A

Competence reduced
Deposits heaviest load on sides
Finer sediments further away
Successive floods, builds up

49
Q

Braiding formation key terms

Yellow River in China

A

Discharge variable - melt water in day, seasonal
When discharge falls, river spreads laterally, deposition
Sediment builds up, eyots
Can become colonised, vegetation
Often eroded as river changes shape

50
Q

Deltas formation key terms

A

Velocity, competence, capacity falls - deposition
Hydraulic radius reduced, inc wetted perimeter as river spread laterally
Flocculation
Sediment can build up, split channel
Repeats, distributaries

51
Q

3 types of sediment in deltas

A

Topset beds: made up of larger bedload
Foreset beds: middle-sized load, deposited further, form steep like wedges
Bottomset beds: finest sediments, travel furthest before low velocity and flocculation occurs

52
Q

Bird foot deltas

A

Dominated by an extruding finger like branch of deposition. Fewer distributaries and fine sediments. Formed due to weaker ocean processes and high discharge.

53
Q

Arcuate deltas

Nile

A

Gentle sloping shoreline, distinct pattern of branching distributaries, dominated by coarser material.

54
Q

River terraces formation key terms

A

Formed when rejuvenated river cuts down through a floodplain, leaving old floodplain above present level of river.

Terraces cut back as new valley is widened by lateral erosion.

55
Q

Paired terraces

A

On same level of each side of channel and so indicate rapid down cutting.

56
Q

Unpaired terraces

A

Occur when fall in base level is slower. Terraces present on different sides of channel at different levels due to lateral erosion - through meander migration.

57
Q

Incised meanders

A

If sea level continues to fall for an extended period of time, knickpoint extends upstream beyond the middle course.

Entrenched
Ingrown

58
Q

Entrenched meanders

A

Caused by rapid vertical erosion or when valley sides are more resistant to erosion, creating a winding gorge.
Can happen when uplift is more rapid and results on a symmetrically shaped cross-profile.

River Wear, Durham

59
Q

Ingrown meanders

A

Occur when vertical erosion is slower, over a longer period of time. Meander has time to erode laterally as well as vertically to form an asymmetrical river valley with steep cliffs on the outside bend.

River Wye, Tinton

60
Q

Knickpoints

A

Sudden change in river’s gradient and mark the point at which the river is cutting down due to rejuvenation.
Form river terraces.
Begins at sea level and retreats up long profile. Knickpoint is where old profile joins new. Usually marked by waterfalls, rapids.

61
Q

Dynamic equilibrium of a river valley

A

All factors in balance (kinetic energy for water transport with no excess for erosion or deposition).

If volume and load change both long profile and channel morphology will also change.

62
Q

The Impact of rejuvenation on a river valley

A

If sea level falls relative to level of land rejuvenation will occur. New base level - potential energy inc.

63
Q

Isostatic change

A

When land rises relative to sea (result of crustal movements).

64
Q

Eustatic change

A

When sea level falls/rises (usually due to ice caps melting/growing).

65
Q

Physical causes of flooding

A 
Excessive rain over long time
Intensive rain over short time
Snow melt
Climatic hazards (hurricanes)
Nature of drainage basin
Relief
66
Q

Influence of human activity on flooding

A

Urbanisation
Deforestation
River management
Global warming

67
Q

Magnitude frequency analysis

A

Used to predict probability of a flood of a particular magnitude happening. Based upon reccurance intervals and highest peak discharge recorded every year.

68
Q

Soft engineering characteristics

A

Cheaper
Sustainable
Don’t affect environment

69
Q

Hard engineering characteristics

A

Expensive
Unsustainable
Changes/damages environment

70
Q

Soft engineering techniques

A

Do nothing
Warn people
Afforestation
Land use zoning

71
Q

Hard engineering techniques

A

Build dams/reservoirs
Levees
Dredging
Straightening rivers

72
Q

Management advantages and disadvantages of:

Do nothing

A
  • discourage new floodplain dev
  • flooding continues
  • costly to recover damage
  • doesn’t prevent flooding
    + cheap
    + river naturally floods
    + fertile silt/water supply for farmers
73
Q

Management advantages and disadvantages of:

Land use zoning

A
  • changes/damages environment
  • difficult to move settlements and communications
    + cheap
    + promotes suitable land use
    + quick to implement
    + effective for a long time
74
Q

Management advantages and disadvantages of:

Build dams/reservoirs

A
  • high construction
  • long time to build
  • damages environment
  • ugly
  • if breaks disaster
    + reduces flooding and costs
    + promotes multi-purpose use
    + built in upper basin
75
Q

Management advantages and disadvantages of:

Warning people

A
  • useless if ignored
  • doesn’t solve problem
    + allows evacuation
    + less flood damage
    + requires good communication network
76
Q

Management advantages and disadvantages of:

Levees

A
  • expensive
  • serious flooding if breached
    + reduces flooding
    + increase channel capacity
77
Q

Management advantages and disadvantages of:

Dredging

A
  • affects local eco-systems
  • costly
  • temporary
    + inc channel capacity
    + reduces flooding
78
Q

Management advantages and disadvantages of:

Afforestation

A
  • trees may not be native - affect ecosystem
    + low cost
    + improve environment
    + wood can be used if sustainably done
79
Q

Management advantages and disadvantages of:

Straightening rivers

A
  • may inc flooding downstream
    + reduces flooding
    + remove excess quicker
    + faster transfer of water
80
Q

Flood management scheme

Three Gorges Dam, China
Benefits

A

Socio-economic: afford protection from 1in100year flood, save lives and livelihoods
Economic: hydropower provide 10% China’s needs, create jobs, enable 5000 vessels to reach Chongqing at all times of year, water supply for towns
Environmental: reduced air pollution as hydropower replaces thermal power, reduced siltation in lakes

81
Q

Flood management scheme

Three Gorges Dam, China
Costs

A

Socio-economic: some settlements completely submerged, some people have to be moved, some to higher altitudes-poorer soils-poorer quality of life, loss of social tradition(live in same place as born)
Economic: loss of businesses as submerged, $24bn, decreased tourism as 1200 sites of cultural heritage drowned
Environmental: increased pollution(sewage, drowned factories toxicate water), siltation if reservoir, ecosystems affected, large dams can cause earthquakes

82
Q

York 2000 Flood

Causes

A

Physical causes: catchment area 3000km2, relief steep high runoff, vegetation heather moorland low interception, climate heavy rainfall
Human causes: farming-cattle eat grass low interception high runoff, urbanisation-impermeable surfaces-drains-water to river ouse quick
Specific to flood: wettest autumn on record, series pf deep depressions from atlantic, global warming wetter winters

83
Q

York 200 flood

River management strategies

Effects

A

Clifton ings: natural floodplain: store 2.3m3: 1982 embankments raised £1.25m
Almery terrace: concrete floodwalls with rubber sealed gates protect houses
Effects: >300 homes flooded, residents evacuated, businesses flooded-Kings Head pub loss of revenue, high costs to repair, city centre car parks flooded, rail track maintenance paused due to flooding

84
Q

Bangladesh Flooding 2004

Climatic processes

A

Summer:land warmer:low pressure:monsoon winds bring moist air from sea
Winter:land cold:high pressure:dry winds blow out from land to sea
Random variations of intensity, flood
One of wettest climates on record, 1525 mm rain/year hills:5080mm
Brahmaputra river swollen by rain, himalayan burst dam, flooded B dozens killed, millions to seek refuge.
4 days underwater, ave rain 300mm per day, himalayan snow melt every year

85
Q

Bangladesh Flooding 200

Terrestrial processes

A

Relief rainfall in himalayan mtn. feeds rivers.
Most of B next to deltas of many rivers flowing from himalaya
1/3 country floods yearly
Approx 80% fertile land (fplain) prone to severe flooding which irrigates crops and adds fresh silt to padi fields keeping fertility.
Most of B is under 10m above sea level.

86
Q

Bangladesh Flooding 2004

Human activity

A

Global warming
Extraction of groundwater for irrigation has lowered water table.
Use of water upstream for irrigation and reservoirs has reduced amount of silt deposited.
More urbanisation, higher peak discharge and shorter lag time.
Pop growth pressure on food so more land farmed so less interception-landslides/deposition-dec channel capacity.

AS Geography (4 decks)

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