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EAS 205 > Flooding > Flashcards

Flooding Flashcards

1
Q

What are the steps of the hydrologic cycle?

A
  1. evaporation
  2. condensation
  3. precipitation
  4. runoff
  5. infiltration
  6. percolation

(repeat)

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2
Q

Is the water flow of the North Saskatchewan River relatively fast?

A

no

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3
Q

stream vs river

A
  • stream - body of flowing water confined to a channel, regardless of its size
  • river - major branch of a stream system
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4
Q

drainage basin

A

region from which stream draws its water supply

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5
Q

where are the divides of a drainage basin usually found?

A

usually between countries/provinces

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6
Q

stream discharge? units? calculation?

A
  • volume of water that passes a given point in a given time through a channel of a certain width and depth; m^3/s
  • cross sectional area x velocity of flow
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7
Q

laminar flow

A
  • straight or gently curved streamlines run PARALLEL to one another (no mixing)
  • characteristic of SLOW rivers or along EDGES of FAST rivers
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8
Q

turbulent flow

A
  • streamlines mix, forming eddies
  • characteristic of FAST rivers
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9
Q

How do streams do work?

A

transport sediments down hill

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10
Q

total sediment load

A

stream’s capacity

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11
Q

stream’s competence

A

stream’s ability to carry a material of a given size

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12
Q

How is capacity related to discharge?

A

faster the stream flows, the more water is present; the more (and larger) material can be moved

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13
Q

How does stream velocity impact sediment sorting?

A
  • slow water = fine-grained sediments
  • fast water = wide range of grain sizes
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14
Q

TRUE or FALSE: sediments are commonly WELL SORTED by size and density

A

TRUE

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15
Q

graded stream? are low spots filled in/eroded? high spots?

A
  • stream in which various factors combine to yield an average of neither erosion nor sedimentation
  • AT EQUILIBRIUM
  • low spots filled in
  • high spots eroded
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16
Q

What is the velocity of a stream largely dependent on?

A

its gradient - steepness of a stream’s channel

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17
Q

base level? What happens to gradient as the stream approaches base level?

A
  • base level = lowest elevation to which a stream can flow
  • gradient DECREASES as it reaches the base level
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18
Q

What is one way that the base level of a stream can be changed?

A

human intervention –> BUILD A DAM

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19
Q

On what kind of gradients do meandering streams often occur? Are they erosive? if so, what materials do they erode?

A
  • occur on gentle gradients
  • erode unconsolidated sediments and weak bedrock –> carry FINE sediments
  • path may shift significantly with erosion and deposition
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20
Q

On what kind of gradients do braided streams often occur? Are they typical of low or high sediment loads?

A
  • many diverging and merging channels
  • steep gradient
  • high sediment load
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21
Q

Describe the formation of a braided stream during low discharge period (summer).

A
  • high velocity, high sediment streams flow over nearly flat, easily eroded terrain
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22
Q

Describe the formation of a braided stream during high discharge period (spring snow melt).

A
  • high velocity, high sediment streams does NOT form OXBOW BENDS
  • instead, cuts across soft sediments at edges of existing channels, creating braided channels
23
Q

When do braided streams usually form? (high or low discharge period)

A

high discharge period (spring snow melt)

24
Q

Describe the formation of a meandering stream.

A
  • current faster at outside banks, which are eroded
  • sediment deposited at inside banks, where current is slower –> FORM POINT BARS
25
Q

TRUE or FALSE: building bridges can disrupt stream flow.

A

TRUE

26
Q

As floodwaters spread out over the floodplain, what happens to the velocity and the capacity of a stream?

A

decrease velocity and capactiy

27
Q

What are natural levees and how are they formed?

A
  • ridges of coarse material that confine the stream within its banks between floods
  • formed by successive floods
28
Q

What is a hydrograph? What does it record? why is it useful? What is on the vertical axis? horizontal axis?

A
  • plot of stream discharge at a point over time
  • records fluctuations in discharge or stream height over time
  • usefule to monitor stream behaviour REMOTELY
  • vertical axis = discharge
  • horizontal axis = time
29
Q

TRUE or FALSE: hydrograph does not use a logarithmic scale.

A

FALSE –> IT IS LOGARITHMIC

30
Q

What are some factors that govern flooding?

A
  • excessive rainfall
  • snowmelt off in mountains
  • severe storms
  • hazardous blockage of stream channel (e.g. trees, avalanches)
31
Q

stage vs crest (flood characteristics)

A
  • stage: elevation of water (flood stage = stream exceeds crest)
  • crest: maximum stage is reached
32
Q

upstream flood vs downstream flood vs flash flood

A
  • upstream flood: occurs in small, localized upper part of basin
  • downstream flood: occurs in a larger, lower part of basin
  • flash flood: type of upstream flood; rapid rise of stream stage (water elevation)
33
Q

describe the peak of an upstream vs downstream flood in a hydrograph.

A
  • upstream flood = sharp peak
  • downstream flood = broad peak
34
Q

What is the rate of surface runoff influenced by?

A
  1. ground cover - different rates of infiltration occur with diff soils, rocks, pavement
  2. topography - steepness of terrain determines infiltration vs surface runoff
  3. presence of vegetation - plants provide physical barrier that decrease water velocity; increase infiltration; absorb water
  4. climate - determines level o rainfall and periodicity of storms; frozen soil during spring runoff
35
Q

How can we predict floods?

A

flood-frequency curve

36
Q

What is on the vertical axis vs horizontal axis of a flood-frequency curve? What is the formula for recurrence interval?

A
  • vertical = discharge
  • horizontal = recurrence interval
  • R = (N+1)/M

note: R = recurrent interval; N = number of years; M = ranking of annual maxima

37
Q

How do asphalt and concrete affect flood plains?

A

reduce infiltration

38
Q

How do buildings affect flood plains?

A

replace water volume; raise stream height

39
Q

How does filling in floodplain land affect flood plains?

A

reduce volume

40
Q

How do storm drains affect floodplains?

A

rapid delivery of storm water to streams –> INCREASE IN STREAM HEIGHT

41
Q

how does vegetation loss affect floodplains?

A
  • streams can “silt up”
  • silt reduces stream capacity to rapidly carry water away
42
Q

In general, hos does development affect flood stage for a given discharge?

A

development INCREASES flood stage

43
Q

TRUE or FALSE: building a dam increase flood risk and urban growth decrease flood risk

A

FALSE:
- dam –> decrease flood risk
- urban growth –> increase flood risk

44
Q

How does climate change affect the hydrological cycle and floods?

A

warmer climate –> faster hydrological cycle –> more frequent floods

also sea levels rise

45
Q

How does straightening a stream affect flooding?

A
  • speed up flow and reduce local damage –> decrease risk of upstream flood
  • increase erosion –> higher flood stages downstream –> increase risk of downstream flood
46
Q

TRUE or FALSE: artificial levees contain high discharge, but cause flooding.

A

FALSE: high discharge without flooding

47
Q

Which dam caused earthquakes by their added weight on the rocks?

A

Hoover Dam

48
Q

What is the issue with flood control dams?

A
  • as velocity rapidly decreases at dam site, waters deposit their load –> increase stage –> lead to failure of dam
  • sediment free water released by dams –> erosion downstream
49
Q

which company was fined $1 million for polluting incidents that impacted fish in Alberta?

A

Sherritt

50
Q

which river tailings spill caused downstream communities to not draw water in Alberta?

A

Athabasca River

51
Q

What was the world’s most catastrophic floods caused by?

A

breaching of ice dams of the retreating continental ice sheets

52
Q

Describe the Channeled Scablands. Which 3 rivers encircle the Scablands? How did it form? Which ice sheet? What is the floor made of?

A
  • erosional features result of giant flood during Great Ice Age
  • basalt floor
  • Columbia River, Spokane River, Snake River
  • formation: CORDILLERAN ICE SHEET formed an ice dam, creating Glacial Lake Missoula –> ice dam breach caused 40 catastrophic floods –> Channeled Scablands
53
Q

Describe thermohaline circulation.

A
  1. warm water from tropics goes to poles
  2. water at poles cool from ice and SINK –> deep water formation
  3. water goes back to tropics
54
Q

What drives thermohaline circulation?

A

deep water currents

EAS 205 (16 decks)

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