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Geography > Rivers > Flashcards

Rivers Flashcards

1
Q

What is river discharge?

A

The volume of water going through a point in the river. Measured in cumecs. Can either show annual flow or storm event.

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2
Q

What effects the rate of erosion.

A

Height above sea level, volume of water in the river, gradient of channel.

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3
Q

What is the capacity of a river?

A

The total load of a river at a particular time or location.

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4
Q

What is calibre?

A

The size of a pebble of particle.

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5
Q

What is the competence?

A

The size of the largest sediment particle that can be carried by the river at a particular point or location.

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6
Q

What does the hjulstrom curve show?

A

Shows the relationship between river velocity and competence.
Also shows the processes of erosion, deposition and transport.

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7
Q

What is the hydrological cycle.

A

The circulation of water between the oceans atmosphere and land. It’s a closed system.

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8
Q

What is fall/ settling velocity?

A

The average velocity at which grains are too heavy to be carried at the current velocity so are deposited.

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9
Q

Types of erosion?

A 
Hydraulic action- pressure and force of water
Attrition- smash, rounded off, smaller 
Abrasion- rub, scrape 
Solution- dissolving   
Cavitation
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10
Q

Depositional land forms?

A

Delta’s
Braided channels
Floodplain
Levees

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11
Q

What is brackish water?

A

When salt and fresh water mix.

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12
Q

What is alluvial deposit?

A

Fine sediment deposit.

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13
Q

Types of transportation?

A

Traction- boulders
Suspension- silt
Solution- limestone
Saltation- cobbles

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14
Q

What factors increase downstream?

A 
Discharge 
Channel width
Channel depth
Average velocity 
Load capacity
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15
Q

What factors decrease downstream?

A

Calibre
Roughness
Gradient

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16
Q

Pothole formation?

A

Small circular hollows in river bed.
Turbulent swirls- eddies
Abrasion on bedload
Scrape out holes

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17
Q

How do Rapids form?

A

Bands of resistant and less resistant rock on bed of river, soft rock gets eroded leaving ridges of hard rock which cause the water to be turbulent and its erosive power increases

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18
Q

Describe interlocking Spurs?

A

They form when the river winds around protrusions which appear to interlock when viewed looking upto a valley.

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19
Q

Three features of river rejuvenation?

A

Incised meanders
Nick points
River terraces

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20
Q

What is river rejuvenation?

A

Isostatic or eustatic change to cause base level to decrease.
Rivers gravitational potential energy is increased.
River wants to get back to graded profile. Vertical erosion dominant to regrade itself.

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21
Q

Term to describe a rivers perfect profile?

A

Graded profile

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22
Q

Word to describe fine sediment?

A

Alluvium

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23
Q

Formation of V shaped valley?

A

Bolders and cobbles can only be transported by traction and saltation- erode bed- intensive vertical erosion
Steep sides

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24
Q

First 3 steps of waterfall formation?

A

Change in gradient
Resistant rock underlain by less resistant bed
Less resistant bed is undercut

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25
Q

Second 3 steps of waterfall formation?

A

Plunge pool forms, vertical erosion
Overhang collapses
Waterfall retreats upstream, gorge sometimes formed

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26
Q

Precipitation?

A

All forms of moisture that reach the earths surface

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27
Q

Evaporation?

A

The transformation of water droplets into water vapour due to heat

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28
Q

Evapotranspiration?

A

The loss of water from a drainage basin into the atmosphere from the leaves of plants

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29
Q

Surface storage

A

The total volume of water held on the earths surface in lakes, ponds and puddles

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30
Q

Groundwater storage

A

The storage of water underground in rock strata

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31
Q

Infiltration?

A

The downwards movement of water into the soil surface

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32
Q

Percolation?

A

The gravity flow of water within soil and through permeable rock

33
Q

Through flow

A

The movement of water downslope within the soil layer

34
Q

Groundwater flow?

A

The deeper downward movement of water through underlying rock strata

35
Q

Dynamic equilibrium?

A

Rivers changing to reach a balanced state.

36
Q

Velocity definition?

A

The speed in a specific direction at which a body of water moves

37
Q

Interception?

A

The prevention of water reaching the earths surface by trees and plants

38
Q

Another term for drainage basin?

A

Catchment area

39
Q

Watershed?

A

A boundary between two drainage basins

40
Q

What is vegetation storage?

A

Water that has been taken up by plants

41
Q

What are rocks that hold water?

A

Aquifers

42
Q

What is the water balance?

A

Shows the balance between inputs and outputs.
Affects how much water is stored in the basin
Used to show seasonal patterns

43
Q

What happens to the water balance during wet seasons?

A

Precipitation exceeds evapotranspiration.

Water surplus- ground stores fill - more run off & increased discharge

44
Q

What happens in drier season?

A

Precipitation is lower than evapotranspiration.
Ground stores are depleted.
End of dry season there is a deficit but ground stores are recharged next wet season.

45
Q

What is a hydrograph?

A

Graphs to show the discharge at a certain point of the river. Storm hydrograph shows this following a storm event

46
Q

Lag time?

A

Delay between peak rainfall and peak discharge.

47
Q

What does a shorter lag time mean?

A

Will increase peak discharge as more water will enter the river during a shorter period of time.

48
Q

Drainage basin characteristics to affect lag time?

A

Gradient
Size
shape
Number of tributaries

49
Q

What is a hydrograph with a steep rising limb?

A

Flashy

50
Q

Rising limb?

A

Part of the graph leading up to peak discharge. Shows the increase in discharge as rain water flows into river

51
Q

Other factors affecting lag time?

A 
Saturated soil
Rock type- aquifers 
Soil type- sandy or clay
Vegetation- deciduous trees
Precipitation- rainfall and snow
Temperature
52
Q

Human factors affecting lag time?

A

Urbanisation
Impermeable surfaces- concrete
Drainage systems- pipe flow

53
Q

What is bed load?

A

Material transported by traction and saltation.

54
Q

Why do silt and clay require a higher velocity to erode?

A

As they stick together so are harder to dislodge.

55
Q

What is the critical erosion velocity curve?

A

The minimum velocity required to erode and transport material of different calibre.

56
Q

What is the other curve of the hjulström curve?

A

Mean settling velocity curve

57
Q

What is the long profile?

A

A diagram to show how a river changes from source to mouth by showing the height of the river above base level.

58
Q

Base level?

A

The highest point a river can erode to - sea level

59
Q

Upper course?

A

Most gpe
Steep gradient
High channel roughness- turbulence
Vertical erosion dominant

60
Q

Why does velocity increase downstream?

A

GPE is converted to kinetic energy.

Channel is smoother so less friction.

61
Q

What is the wetted perimeter?

A

The total length of the banks and bed in contact with water

62
Q

What does a small hydraulic radius mean?

A

That a river is less efficient.
More friction so more energy loss.
Reduced velocity

63
Q

What can increase wetted perimeter?

A

Channel roughness

Protrusions and angular boulders

64
Q

How to work out hydraulic radius?

A

Cross section divided by wetted perimeter

65
Q

Why does calibre decrease downstream?

A

Lots of attrition in middle stage.

66
Q

Why are lower stage valleys wide with gentle sloping sides?

A

Increased floodplain due to deposition.

67
Q

Magnitude?

A

Size of flood

68
Q

Term to describe how often a specific level of flood will occur?

A

Recurrence interval

69
Q

Hard engineering?

A

Dams
Levees
Channel straightening
Diversion spillways

70
Q

Soft engineering strategies?

A

Land use zoning
Afforestation
Wetland creation
River restoration

71
Q

Floodplain formation?

A

Water overspills from bank and floods the flat land
Floodwater is shallow and has extensive wetted perimeter
Alluvium is deposited

72
Q

Levees formation

A

River floods
Coarser material deposited closest to banks
Builds up overtime

73
Q

Braided channel formation?

A

Coarsest material dropped
Blocks main channel
Channel no longer competent to transport material
Channel Subdivides into a series of converging and diverging channel to seek easier a route

74
Q

When may river velocity drop?

A

Discharge decreases
At mouth as sea absorbs energy
Increased friction

75
Q

Delta formation?

A

Energy decreases
Sediment deposited at mouth
River braids into distributaries to reach the sea

76
Q

First 3 steps of meander formation?

A

River takes most efficient route
Riffles reduce hydraulic radius
Alternatively water flows over pools

77
Q

Last three steps of meander formation?

A

Water will swing to avoid riffles- increases turbulace
Helicoidal flow transports eroded material from outside and deposits inside
Water travels fastest on outer bend

78
Q

Oxbow lake formation?

A

Sinuosity of meander increase. Neck of start and end of bend get narrower.
Flood event- river breaks through
Straight path current more dominant
Meander cut off

Geography (6 decks)

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