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Geological natural hazards > Flooding_intro > Flashcards

Flooding_intro Flashcards

1
Q

What are type A,B and C flooding?

A

A - flash
B - long duration
C - long duration & high magnitude

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2
Q

What is an example of a type A flood?

A

Boscastle 2004

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3
Q

What was the combination of factors that lead to flooding in boscastle?

A

weather conditions (relatively short time
scale intense rainfall) & physical setting (small, steep catchment with impermeable geology)

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4
Q

How much rain was their at boscastle?

A

75mm in ~2hrs

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5
Q

What were the effects of the boscastle flood?

A

200 homes/ businesses damaged
No fatalities

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6
Q

How is flood risk usually attributed?

A

On a catchment basis

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7
Q

What is an example case study for a type B flood?

A

Gloucetershire 2007

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8
Q

What was the cause and effect of glocestershire 2007?

A

78mm rain ~12hrs
widespread flooding across the Uk (5000 homes, no fatalities)

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9
Q

What is another name for type C floods?

A

Mega floods

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10
Q

What is usually the cause of type C floods?

A

Failure of a retaining structure (glacial outbursts)

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11
Q

When is an example of a type C flood?

A

Middle Pleistocene – Northern
Europe

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12
Q

What were the effects of the Middle pliestocene type C flood?

A

Evidence of large-scale scours, streamlined hills, giant bars and run-up deposits (initial wide spreading of flood waters). And trench-like channels (concentrated flow of later drainage)
Set the drainage pattern of all subsequent glacial retreat/post-glacial drainage

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13
Q

What were peak discharges from the Mid pleistocene type C?

A

465,000 to 673,000 m*3/s

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14
Q

what as the flow depth of the Mid- pleistocene type C?

A

87m deoth with velocity of 7m/s

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15
Q

What might some future causes of mega flood be?

A

Failure of infrastructure
Climate change glacial retreat

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16
Q

How can intensity of rainfall events be calculated?

A

divide rainfall (depth of water) by duration

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17
Q

What is the weighting of intensity and duration like for the different flood types?

A and B

A

Intensity is important in flash floods (type A), whereas overall rainfall is more important for long duration floods (type B)

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18
Q

What is the return period/ probability of rain fall events?

A

The liklihood of a similar scale event occuring in an area again (1 in 100yr event)

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19
Q

What is the tempora spacong of floods like?

A

Independant and random

20
Q

WHat are structures in vulnerbale flood areas designed to be like?

A

withstand a specific max flood for a specific time (return periods can calculate failure)

21
Q

How much of total water does flooding account for?

A

2% of 0.9% of 3% of all water

22
Q

What is the fundamental component of flooding?

A

precipiation

23
Q

What parts of the water balance equation can be altered to reduce the effects of flooding?

A

Evapotranspiration
Change of water storage

24
Q

What is the weakness of the water balance equation?

A

1 dimensional only looks at one point in time and space not accouting for when and where the rain falls

25
Q

What are the 3 main types of runoff?

A

Over land flow
Throughflow
Ground flow

O and T are quick flow G is base flow

26
Q

Will water that ends up in ground flow influence the discharge of the food event?

A

No as the water will be moving at a much flow rate

27
Q

What are the types of overland flow?

A

– Infiltration excess flow (Hortonian)
– Saturation excess flow
– Return flow

28
Q

What are the ypes of throughflow?

A

Unsaturated throughflow
– Saturated throughflow
– Pipe flow

29
Q

WHat is pipe flow?

A

Floe through relic root systems which connect pore spaces

30
Q

What influeneces throughflow?

A

Soil texture and pipe flow

31
Q

What can evapotranspiration also cover?

A

Infiltration and canpoy stroage in leaves
Taking water from the subsurface storage via roots (allows more infiltration)

32
Q

Will the same type of flood happen in different catchments ?

A

No as there will be different triggers, topography and nature of precipitation

33
Q

WHat are some examples of less common causes of floods? (anything other than rain)

A

Snow and ice melt
Ice jams (large ice block dam)
Landslides (landsldie dams)
Failure of dams and control works

34
Q

Why are floods from structure failure seen as more devestating/ unexpected?

A

Due to the comfort in the thinking that the measures will remain in place

35
Q

What are flood intensifying factors?

A

Driver (volume of water)
Basin factors stable i.e. area
Basin factors variable i.e. Climate and geology
Drainage network
Channel factors

36
Q

What is the boscastle catchment like?

A

SMall with narrow steep valleys typical of cornish area

37
Q

What is the probability of the boscatle flood like over the whole or cornwall?

A

Relatibely high with many areas being sensitive to a similar event

38
Q

How does the distribution and intensity of rainfall in a catchment affect flooding?

A

If lower intensity rain is in the process of enetering the channel and then a high intenisty period occurs and overland flow takes place both rain packets will reach the flood area at the same time

39
Q

What type of flood was Valencia?

A

Type A - with flood water being able to carry and stack cars
Dirty flood (sewage and lots of sediment in the water)

40
Q

Why was valencia primed for a flood event?

A

The ground was already saturated pre-event

41
Q

WHat flood type is the UK most used to experiencing?

A

Tybe B

42
Q

Why is type B flooding so damaging?

A

As rainfall occurs for a long time over a wide part of the catchment with each time a head waters meet the volume combines

43
Q

Why is prediction of type B floods easier?

A

As you know how much rain is in the system so can tell what water levels will be at a certain point alomg the river

44
Q

What was the cause for the pleistocene mega flood?

A

Glacial retreat which created a melt lake which when ice had retreated enough exposed a topogrpahic low allowing spillage

45
Q

WHy is return period and risk used for structural deisgn for flooding?

A

depeding on lifetime will need ridgity to different levels of event i.e., dams with long life time 1 in 10000 yr event

46
Q
A

Geological natural hazards (20 decks)

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