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Geohazard > Flooding - Flood Hazards > Flashcards

Flooding - Flood Hazards Flashcards

1
Q

this refers to when a normally dry areas of the land become inundated

A

flooding

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2
Q

what is the most common way that a flood can occur?

A

when excessive amounts of overland flow cause an increase in discharge, river channel can no longer hold all of the flow of water and will eventually overflow its banks

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3
Q

scientists use _________ and __________ to compare floods in a quantitative manner

A

stream discharge and height

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4
Q

is the height at which a river begins to overflow ots banks

A

flood stage

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5
Q

how is discharge computed?

A

multiplying cross sectional area of a river to its average velocity

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6
Q

t or f: flood stage gets higher as you go further from banks

A

t

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7
Q

the severity of flood is quantified by measuring wither __________ or _____

A

stream discharge or stage

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8
Q

refers to any level where stream has gone over its banks

A

flood stage

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9
Q

t or f: there is an inverse relationship between discharge and height

A

F (direct)

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10
Q

why are floods difficult to predict?

A

because they are largely dependent on specific weather events that have a high degree of natural variability

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11
Q

t or f: flood frequency does not tell us when a flood of a certain magnitude will occur, but rather the probability or chance of it happening

A

t

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12
Q

represents the frequency of a particular discharge value can be expected to repeat itself

A

recurrence interval

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13
Q

what does a 100-year recurrence interval mean?

A

on average, 100 years should pass before that same discharge will occur again

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14
Q

t or f: a 100-year flood could take more than 100 years to repeat, but could just as easily reoccur in less than 100 years

A

T

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15
Q

t or f: low discharge events occur frequently more than high discharge events

A

t

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16
Q

the inverse or reciprocal of recurrence interval (1/RI)

A

percent probability

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17
Q

a 10-year flood has a percent probability of?

A

10%

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18
Q

what does a 10% probability of a flood means?

A

10 percent probability that a flood will take place in any given year

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19
Q

this tell us how often we can expect floods of a certain size

A

recurrence interval

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20
Q

indicate the chances of occurring of flood of certain size

A

percent probabilities

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21
Q

what is the difference between recurrence interval and percent probabilities?

A

recurrence interval tell us how often we can expect a flood of certain discharge can occur, whereas percent probabilities can tell us their chances of occurring

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22
Q

the reliability of recurrence interval is dependent on the ___________

A

availability of historical discharge records

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23
Q

formula for recurrence interval

A

RI = (N+1)/M

where:
N = number of values in the record
M = rank of the discharge

24
Q

what is the unit for recurrence interval?

A

year

25
Q

the potential for flooding in a given area naturally increases as the ________ and _________ of rainfall increases

A

intensity and duration

26
Q

rainfall events might range from _______ to ______

A

light to torrential rains

27
Q

t or f: light rains are steady and may last for few days while torrential rains only last for a few minutes to several hours

A

t

28
Q

another important factor associated with rainfall is the ____________

A

size of the area over which the rain falls

29
Q

relatively small storms that tend to keep moving and may generate intense rains, but flooding is more localized

A

isolated thunderstorm

30
Q

storms that move inland from the ocean and can drop tremendous amounts of water over large areas, thereby producing widespread flooding

A

large regional storms

31
Q

a generic term used by meteorologists to describe a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has closed, low-level circulation

A

tropical cyclone

32
Q

The weakest tropical cyclones are called

A

tropical depression

33
Q

when is a tropical cyclone considered a hurricane or typhoon?

A

when its wind reaches 74 miles per hour or higher

34
Q

where is the term “hurricane” used?

A

Atlantic ocean, Eastern Pacific ocean

35
Q

where is the term “typhoon” used?

A

Northwest Pacific

36
Q

where is the term “tropical cyclone” used?

A

South Pacific and Indian Ocean

37
Q

what are the natural factors that affect flooding?

A
  1. nature of precipitation events
  2. ground conditions
  3. vegetation cover
38
Q

the ability of ground to absorb water

A

infiltration capacity

39
Q

explain how infiltration capacity plays a critical role in flooding

A

water that is unable to infiltrate will br eventually forced move as overland flow

40
Q

the actual rate at which at which water can infiltrate is determined by the _______, _______, and ________

A

slope of the surface, type of ground material, and moisture content of material

41
Q

t or f: as slope becomes progressively steeper, infiltration capacity decreases

A

t

42
Q

t or f: gravel and sand-rich soils have higher infiltration capacity than clay soils

A

t

43
Q

t or f: infiltration capacity decreases as soil becomes more saturated

A

t

44
Q

how can vegetation cover affect flooding?

A

vegetation intercepts and stores a certain fraction of rain, thereby preventing it from reaching the land surface and moving as overland flow

vegetation enhances absorptive capacity, decreasing runoff and overland flow

45
Q

the potential for flooding depends on:

A
  1. how much and for how long precipitation rate exceeds the infiltration rate
  2. size of the area of which the rain falls
  3. vegetation density
46
Q

floods that have short duration with relatively high peak discharge

A

flashfloods

47
Q

t or f: flashfloods generally affect only localized areas

A

t

48
Q

t or f: flashfloods are dangerous due to their sudden nature

A

t

49
Q

why are flashfloods dangerous?

A

they are sudden in nature, which means people have less time to evacuate

50
Q

flashfloods are also referred to as

A

upstream floods

51
Q

t or f: flashflooding can occur in downstream areas

A

t

52
Q

where in downstream areas can flash floods occur?

A

along small tributaries

53
Q

t or : flashfloods can also occur from sudden failure of dams

A

t

54
Q

can be defined as one where the river leaves its channel farther down in its drainage basin, flowing out into floodplain and inundating large areas of the valley floor

A

downstream flood

55
Q

what does downstream flood inundate?

A

valley floors

56
Q

what causes downstream floods?

A

regional accumulations of water higher up in the drainage basin

57
Q

how does downstream flood differ from flashfloods?

A
  1. lag time between the rain event and peak discharge (higher on downstream floods)
  2. length of time the river remains above flood stage (higher on downstream floods)

Geohazard (25 decks)

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