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GEOGRAPHY UNIT 1 > Rivers, Floods and Mangement > Flashcards

Rivers, Floods and Mangement Flashcards

Mr Hamshaw's lessons

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1
Q

Define: Hydraulic Radius

What is it a measure of?

A

The cross-sectional area of the river / the wetted perimeter. A measure of efficiency of a river.

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2
Q

Define: Knickpoint

A

Occurs when isostatic/ eustatic movement of water levels give +ve or -ve water base level.

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3
Q

Define: Lagtime

A

Lagtime is the time between the rainfall and this water reaching the river.

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4
Q

Define: Incised meander

A

A section of meander that has more GPE so is eroding vertically and cutting an asymmetric channel for itself.

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5
Q

Define: Ingrown meander

A

A section of meander that has more GPE so is eroding vertically and cutting a symmetric channel for itself.

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6
Q

Define: Alluvial deposits

A

A deposit dropped by the river when it loses competence or exceeds its capacity.

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7
Q

Define: Pot holes

A

When turbulent eddies of water and bubbles erode vertically and pop causing holes and dips in the river banks and bed.

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8
Q

Define: Braided channel

A

A braided channel is when a river loses competence and drops load which blocks up its own channel. It then flows around this forming a new channel. Happens lots of times to form the braided channel.

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9
Q

Define: Flood plain zoning

What is prioritised near the river and what is not?

A

Flood plain zoning is where the land around a river is split off into sections of what can be built on these areas, with no buildings right by the water side and vegetation is prioritised.

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10
Q

Define: Evapotranspiration

A

Part of the hydrological cycle, the evaporation from the ground and trees and transpiration from leaves.

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11
Q

Define: Interception / Secondary Interception

A

Interception is rainfall being stopped by vegetation and trees, slowing the lag time of it reaching the river.

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12
Q

Define: Antecedent rainfall

A

Antecedent rainfall is previous rainfall, past 2 weeks ish.

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13
Q

Define: Competence

A

The maximum size of material the river can carry.

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14
Q

Define: Capacity

A

The maximum amount of material the river can carry.

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15
Q

Define: Corrasion

A

Same as abrasion, the effect of rocks eroding the banks of the river.

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16
Q

Define: Rejuvination

A

Is where regrades due to having more GPE so has become like a stream in its upper course again.

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17
Q

Define: Diversionary Spillaway

A

Hard engineering technique used to make a alternate channel for water to flow down during times of high discharge.

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18
Q

Define: Corrosion

A

The water’s chemical composition erodes the river banks and bed.

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19
Q

Define: Hard/ Soft engineering

A

Hard engineering is big structural constructions to manage flood risk. Soft engineering is more relaxed, cheaper engineering compared to hard.

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20
Q

Define: Isostatic and Eustatic

Why would these things change?

A

Isostatic is changes in land level and Eustatic is changes in water level.
Isostatic rebound and Global warming/Ice ages.

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21
Q

Define: Confluence

A

Where two rivers meet and join together.

22
Q

Define: Watershed

A

The line along the top of a hill that marks the drainage basin of an area.

23
Q

Describe how water reaches the river channel? (5 answers)

A
  • Channel precipitation.
  • Surface run-off.
  • Inflitration of the soil.
  • Groundwater flow.
  • Root flow in plants/leaves.
24
Q

Precipitation = ________ + _________ +/- ________

A

Evaporation + Runnoff +/- storage.

25
Q

What months of the year are times of “Soil Moisture Recharge” ?

A

September to December.

26
Q

What months of the year are times of “Potential Moisture Surplus” ?

A

January to April.

27
Q

What is the “Water Budget” ?

A

The Water Budget is the amount of water there is in the soil at different times of year.

28
Q

What months have a “Potential Moisture Deficit” ?

A

May to August.

29
Q

What 6 factors effect whether a flood hydrograph is normal or flashy?

A
  • Antecedent precipitation (saturated and unsaturated ground).
  • Land use (permeable or impermeable surfaces).
  • Rock and soil type (permeable or impermeable surfaces).
  • Vegetation type and season (deciduous trees and woodland).
  • Precipitation type, length an intensity.
  • Drainage basin relief, size, shape and height.
30
Q

Define: Abrasion

A

Rocks breaking down the river bed and banks by rubbing against it.

31
Q

Define: Attrition

A

Rocks colliding in the water and cracking and breaking up against one another.

32
Q

Define: Hydraulic action

A

The erosive power of the water eroding the bed and banks.

33
Q

Define: Cavitation

A

Air bubbles getting into rock cracks and exploding and causing holes and fractures in the rock.

34
Q

Define: Saltation

A

Large stones being bounced along the river bed.

35
Q

What does the Hjulstrom curve show?

A

The Hjulstrom curve shows the different processes going on in the river with different particle sizes and different rover velocities.

36
Q

Above what velocity is clay and silt eroded?

A

Above 100 cm/s

37
Q

What velocity is clay and silt deposited?

A

It never is.

38
Q

At high velocities there is little difference between what and what? Especially with what size of particles?

A

Erosion and deposition, especially with big, heavy particles.

39
Q

Which particle type is the easiest to be picked up?

A

Sand particles.

40
Q

What is the Bradshaw model?

A

The model shows us the characteristics of a typical river from source to mouth.

41
Q

Which characteristics get greater/bigger/more to the mouth of the river? (7 characteristics).

A
  • Discharge.
  • Channel width.
  • Channel depth.
    THEREFORE CROSS SECTION.
  • Load quantity
  • Hydraulic radius
  • Velocity
42
Q

Which 4 characteristics reduce/get smaller/less downstream?

A
  • Load particle size
  • Gradient
  • Channel bed roughness
    THEREFORE DECREASE IN WETTED PERIMETER.
43
Q

Name some V shaped valley characteristics. Give a named example. (At least 5)

A
  • 45 degree angle sides.
  • River fills bottom of the valley.
  • Interlocking spurs.
  • Narrow channel.
  • Large angular bed load.
  • Slow velocity.
  • Small discharge.
  • Upper course.
    Example: Grindsbrook Clough, Edale.
44
Q

Name some waterfall characteristics. Give a named example in the UK. (At least 5)

A
  • Hard rock top layer.
  • Softer rock below.
  • Plunge pool formed.
  • Hard rock overhang.
  • Water pressure causes it to crack and break off.
  • Upper course feature.
  • Corrasion, Abrasion and Hydraulic action.
    Example: Thornton Force, N. Yorkshire.
45
Q

Names some meander characteristics. Give a named example. (At least 5)

A
  • Middle course
  • Caused by deeper pools of water being faster.
  • Also caused by riffles of slower moving water.
  • Forms sinuous shape across the floodplain.
  • More erosion on inside bend/ Less on the outside bend.
  • Helicoidal (centripetal) flow bounces from inside to inside.
  • Thalweg is lowest point of all water.
  • Undercut bank on outside of meander.
  • Slip-off slope (+ point bars)formed on inside of meander.
    Example: River Thames, London.
46
Q

Name some flood plain characteristics. (At least 3)

A
  • Flat fertile land on either side of a river.
  • Lower course feature.
  • River erodes laterally.
  • Meanders migrate and move.
  • Caused by erosion and deposition.
  • Bluff line is the higher ground that hasn’t been flattened.
    Example: Millhouses Park, Sheffield.
47
Q

Describe the formation of natural levees. Give a named example.

A
  • Occur when river is in flood, spreads out over floodplain
  • Deposits that form them called alluvium.
  • Heaviest material deposited first, closest to river banks.
  • Forms raised lip on the edge of the river.
    Example: Afon Conwy, Wales.
48
Q

Describe the formation of braided channels. Give a named example.

A
  • Drop in water depth and so competence and capacity.
  • Deposits biggest load which blocks river channel.
  • Can’t move the deposit so goes round it.
  • Forms braided channels that diverge and converge.
    Example: Brahmaputra-Jamuna River, Asia.
49
Q

Describe the formation of a delta. Name 4 types of delta. Give a named example.

A
  • Sediment deposited when river meets sea.
  • Whole feature made up of alluvium.
    Types: Cuspate, Arcuate, Estuarine, Lobate (bird’s foot).
    Example: Nile Delta, Egypt.
50
Q

Describe the formation of an oxbow lake. Give a named example.

A
  • Neck of a meander erodes towards each other.
  • Too sinuous so the flow finds a way to flow across neck.
  • This eventually becomes the main route.
  • A crescent shaped lake is left.
  • Eventually dries up.
    Example: Isle of Dogs, River Thames, London.

GEOGRAPHY UNIT 1 (4 decks)

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