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1410 Chap 10 - 14 > Sem#2 Chap 5 > Flashcards

Sem#2 Chap 5 Flashcards

1
Q

Inland floods in non-coastal regions result from:

A
  • Oversupply of rainfall
  • Oversupply of melting snow
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2
Q

Stream floods:

A
  • When water spills over the banks of a stream channel
  • Most inland flooding results from stream flooding.
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3
Q

Areal floods:

A
  • When low areas collect water and become submerged
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4
Q

Urban floods:

A
  • When cities are inundated due to insufficient drainage
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5
Q

Floods also occur when _____
and ______fail.

A

dams and levees fail.

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6
Q

Hydrologists:

A
  • Scientists who study water on and below the land
  • Distinguish between flood types
  • Research stream discharge, competence, and capacity
  • Use spatial data to create flood probability maps
  • Use models to predict flood interval probabilities
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7
Q

Slow-onset floods (development time)

A
  • Develop over days or weeks
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8
Q

Flash floods (development time)

A

Develop over minutes or hours

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9
Q

Runoff:

A

water flowing from an area in response to gravity

  • Overland flow: water flows across land as a thin layer (sheetwash).
  • Stream flow: water flows down a trough or channel.
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10
Q

Stream

A

any flowing body of water in a channel
* Medium-sized streams are called creeks or brooks.
* Large-sized streams are called rivers.

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11
Q

Streams form when ?

A

runoff carves a trough into the ground.
* Downcutting deepens stream channels.
* Headwater erosion lengthens stream channels.

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12
Q

Slide #5 Chap #5

A

Slide #5

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13
Q

Headwater

A

where a stream begins to flow

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14
Q

Mouth

A

where a stream empties into another body of water

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15
Q

Gradient

A

a stream’s slope, in the downstream direction

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16
Q

Longitudinal profile:

A
  • Plots elevation on the vertical axis
  • Plots distance from mouth on the horizontal axis
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17
Q

Floodplains

A
  • Wider than stream channel
  • Submerged during a flood
  • Often contain fertile soil
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18
Q

Base level:

A
  • The elevation below which a stream surface will not drop
  • Local base levels lie upstream from mouth.
  • Lakes and tributaries are local base levels.
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19
Q

Stream flow creates ______ and dissolves _______.

A

sediment and dissolves minerals.

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20
Q

Dissolved load

A

mineral ions in solution

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21
Q

Suspended load

A

silt and clay particles within a stream

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22
Q

Competence

A

the maximum clast size a stream can carry
* Faster flowing streams have greater competence.
* Muddy (denser) streams have greater competence.

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23
Q

Capacity

A

the total quantity of sediment a stream can carry
* Competence and water Alluviumvolume dictate capacity

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24
Q

Alluvium

A

a layer of settled stream sediment

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25
Q

Coarse alluvium settles from _______

A

faster-flowing streams

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26
Q

Fine alluvium settles from __________

A

slower-flowing streams

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27
Q

Bar

A

an accumulation of gravel and sand along or within a channel

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28
Q

Alluvial fan

A

a wedge of sediment deposited at a canyon mouth

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29
Q

Floodplain deposits consist largely of _____ and _______.

A

largely of silt and clay.

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30
Q

Natural levees

A
  • Sediment ridges on the banks of a stream channel
  • Form as water slows and spills into a floodplain
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31
Q

Deltas

A
  • Sediment wedges at the mouth of a stream
  • Form as water empties into a standing body of water
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32
Q

Distributaries

A
  • Small channels cutting across a delta
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33
Q

Delta plains

A

are broad lowlands liable to flooding.

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34
Q

Permanent Streams

A

 Fed by sufficient overland flow, tributaries, and springs
 Stream bed remains submerged
 Water table lies above stream bed
 Common in temperate and tropical regions
 Flow all year

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35
Q

Ephemeral Streams

A

 Fed by insufficient overland flow, tributaries, and springs
 Stream bed is often exposed
 Water table lies below stream bed
 Common in semiarid and arid regions
 Flow only part of the year
 Dry wash/arroyo/wadi: a completely dried up ephemeral stream

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36
Q

Meandering Streams

A

Often flow across broad floodplains with deep alluvium

May carve meandering canyons:
* Base level must drop relative to land surface.
* Stream downcuts into bedrock.
 Course changes are common:
* Water flows faster on outer curves, creating cut banks.
* Water flows slower on inner curves, creating point bars.
Oxbow lakes form when a meandering neck is eroded away.

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37
Q

Evolving Meanders

A

A channel’s position changes within a floodplain as meanders evolve.

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38
Q

Meandering River

A

river with a single channel and high to moderate sinuosity.

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39
Q

Cutbanks (CB)

A

form on the outside of meander bends where the water is accelerated along the outside wall and erodes into the bank.

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40
Q

Point bars (PB)

A

form as sediment is deposited in the
slower water on the inside of the
meander bends.

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41
Q

Thalweg

A

the deepest parts of the channel along the length of the stream bed

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42
Q

 Evidence of channel position changes:

A
  • Abandoned meanders, relict point bars, and oxbow lakes
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43
Q

Braided Streams

A

 Carry large quantities of sediment when flow is high
 When flow slows, sediment settles into elongated bars.
 Stream separates into small channels flowing around bars.
 Channels resemble braided hair.

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44
Q

Braided River

A

a river characterized by multiple,
frequently shifting channels.

  • Common in regions where there is a strong seasonally and monthly variation in stream discharge
  • During short periods of high discharge a braided river carries the coarsest sediment
  • Develop in regions where sediment is readily available
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45
Q

Watershed

A

the land area from which water drains
* Also called catchments or drainage basins

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46
Q

Watershed tributaries feed water into a ______.

A

trunk stream

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47
Q

Trunk stream drains water from ______.

A

watershed

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48
Q

Drainage network includes:

A
  • Watershed’s tributaries
  • Watershed’s trunk stream
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49
Q

Drainage divide

A
  • Elevated land separating drainage networks
50
Q

Continental Divide

A
  • Separates drainage networks flowing into different oceans
51
Q

The Amazon Drainage Network

A

 The largest drainage network in the world
 Drains much of South America
 Continental divide follows the crest of the Andes

52
Q

1st-order streams:

A
  • Small streams
  • No tributaries
  • Near margins of drainage network
53
Q

Low-order streams drain _____ areas

A

small

54
Q

High-order streams drain _____ areas.

A

large

55
Q

Two 1st-order steams merge to
form a 2nd-order stream

A

(just a knowledge thing, repeat for every #stream take 2 to from the next)

56
Q

 A trunk streams is a network’s _______

A

highest-order stream.

57
Q

Stream Discharge

A

The water volume passing a cross-sectional area

58
Q

 Cross-sectional area

A
  • A plane drawn perpendicular to the banks of the stream
59
Q

 Cross-sectional area formula

A

𝐷𝐷 = 𝐴𝐴 × 𝑣𝑣
* D = discharge
* A = cross-sectional area
* v = average water velocity

Reported in m3 or ft3 per second

60
Q

Gauging stations

A

record stage and average velocity.

61
Q

Stage

A
  • A reference elevation just below the streambed
62
Q

Temperate and tropical
places(Discharge Variations):

A
  • Tributaries and springs add water to flow.
  • Discharge often increases downstream.
63
Q

 Arid and semi-arid places(Discharge Variations):

A
  • Water seeps into ground, evaporates, or is removed.
  • Discharge often decreases downstream.
64
Q

Trunk stream discharge (what does it represent)

A
  • Reflects watershed size and climate
65
Q

Turbulence develops from ________

A

shearing water flows

66
Q

(Discharge Variations): Calculations are inexact due to _________

A

friction and turbulence.

67
Q

Flood stage:

A
  • When water rises above a stream bank
  • Significant areas outside channel are submerged.
  • Cross-sectional area and average flow velocity increase.
68
Q

Large elevation increase in flood stage:

A
  • When stream channel lies within a narrow valley
69
Q

Small elevation increase in flood stage:

A
  • When stream channel lies within a low-lying floodplain
70
Q

Discharge changes during a
flood.(increase and decrease explain)

A
  • Increases as flood develops
  • Decreases as flood recedes
71
Q

Discharge resembles a ________

A

bellshaped curve

72
Q

Peak discharge:

A

the highest point on a hydrograph

73
Q

Flood crest:

A

when water reaches highest stage

74
Q

Lag time is the difference between:

A
  • The event triggering flooding
  • Flood crest
75
Q

Slow-Onset Floods

A

 Water rises for days or weeks.
 Water recedes over weeks or months.
 Affect high-order trunk streams in downstream places
 Hydrographs display wide curves.
 Common in Bangladesh, within the Ganges River Delta
 ~80% of Bangladesh’s people live on the Ganges River Delta.
 Flooding requires millions of people to evacuate

76
Q

Flash flood characteristics

A
  • Discharge becomes hazardous in < 6 hours.
  • Discharge increases after a short lag time.
  • Floodwaters quickly recede.
  • Affect small areas
  • Affect low-order streams
77
Q

Hydrographs have a _______

A

narrow, bell-shaped curve

78
Q

Flash Flood Dangers

A

 People and motorists are often caught by surprise.
 Water may flow faster than people can run or drive.
 Helicopters may be required to save people.
 Turbulent water causes rapid erosion.
 Dynamic pressure of sedimentladen water destroys structures.
 Heavy debris batters and buries areas downstream.

79
Q

Rapid melting snow may cause ________

A

flash floods

  • Spring rain melts winter ice.
  • Volcanic eruptions melt glaciers and snow caps.
80
Q

Ice dams:

A

natural walls of ice holding back water

81
Q

Outburst floods result when ______

A

ice dams fail

82
Q

Iceland’s “Jökulhlaup” floods:

A
  • Meltwater accumulates beneath a glacier.
  • Outburst flood results when water breaches glacial toe.
83
Q

Glacial Torrents

A

Immense outburst floods from melting glaciers

84
Q

Ice Jams

A

 Form when river ice breaks up during the spring
 Ice encounters an obstacle and piles up.
 Ice blocks water from flowing downstream.
 Water floods into floodplain.
 Outburst flooding may result when ice jam breaks

85
Q

Areal Flooding

A

 Land is submerged due to heavy rain or rapid snowmelt.
 Flooding occurs without input from a nearby stream.
 May delay agricultural planting
 Farmland and low-lying communities at risk

86
Q

Urban Flooding

A

A flood that inundates a built
environment

 May occur during slow-onset and flash-flood events
 Flood control channels may expedite water removal.

87
Q

Urban Flooding: Two causes:

A

Impermeable surfaces that prevent water infiltration
* Inadequate drainage

88
Q

Urban Flooding: Potential impacts:

A
  • Toxic runoff causing environmental damage
  • Higher flood crest
89
Q

Before urbanization

A
  • Rainwater infiltrates the ground.
  • Less discharge, and peak occurs after a long lag time
90
Q

After urbanization:

A
  • Rainwater flows directly into streams.
  • More discharge, and peak occurs after a short lag time
91
Q

Artificial Levees

A

 Constructed ridges of gravel, sand, and compacted clay
 Built along a stream to confine flow to main channel
 Prevent flooding along many river channels
 Vulnerable to accidental or deliberate damage
* Military conflicts may intentionally damage levees.

92
Q

Artificial Levees: Construction parameters

A

Construction parameters:
* Base should be 3 times wider than height
* May be built atop natural levees

93
Q

Levee Failure: Overtopping

A

Occurs when water rises high enough to flow over a levee
* Water velocity and volume increase.
* Erosive power increases as water flows over levee.
* Water may scour a channel in levee wall.
 May also occur due to:
* Tree roots disturbing soil
* Floating debris colliding with levee wall
* Slumping in levee wall

94
Q

Levee Failure: Underseeping

A

 Also called undermining
 Water pressure difference:
* May force water through levee base
* May force water through sediment beneath levee
 Fountaining may develop:
* Water flows through narrow pathways beneath levee.
* Sand volcanoes may appear.
 Fountaining indicates that a breach is imminent.

95
Q

Levee Failure: Structural Damage

A

 Structural weakness may be caused by:
* Bad concrete
* Poorly compacted clay
* Weak foundation
 Concrete barriers may crack.
 Levee foundation may shift.
 Slumping may occur on either side of levee.

96
Q

Danger Due to Moving Water

A

 Driving across flooded roads can be fatal.
 Water’s dynamic pressure rises with the square of its velocity.
 Even shallow water can easily push vehicles sideways.
 Buoyancy force pushes vehicles upward.
 Flash flood casualties result from people trapped in cars.
 Debris in floodwater often destroys bridges and buildings.
 Floodwaters erode riverbanks.
 Floodwater alluvium may bury streets and buildings.

97
Q

Damage Due to Rising Water

A

 Floodwaters may submerge fields, homes, and businesses.
 Transportation and communication networks fail.
 Animals drown if unable to escape to higher ground.
 Power generation fails, so electricity goes out.
 Floodwater residue contains garbage, sewage, and chemicals.
 Mud and silt muck are left behind as water recedes.
 Secondary disasters of cholera and dysentery are common.

98
Q

Monsoon

A
  • A seasonal reversal in wind direction
  • Wind reversal causes shift in precipitation.
99
Q

South Asia’s intense monsoonal rainy season:

A
  • Intertropical convergence zone (ITCZ) drifts north.
  • Indian Ocean moisture spawns heavy rains.
100
Q

Atmospheric rivers:

A
  • Narrow bands of moist air flowing inland from Pacific ocean
  • Air flows along the south side of a mid latitude cyclone.
101
Q

 Recurrence interval:

A

Average years between two floods of a given discharge or greater

102
Q

How to calculate Recurrence Interval

A

𝑅 = (𝑁/1)÷ 𝑀
* R: recurrence interval
* N: number of years of flood
records
* M: rank of flood, with largest
ranked #1

103
Q

Hydrologists prefer using ____ to report flood likelihood

A

AEP

104
Q

AEP determines likelihood of:

A
  • A flood of a given discharge or greater will occur in a given year
  • AEP is reported as a percent.
105
Q

AEP Formula

A

𝐴 = (1÷𝑅)𝑥100

106
Q

Flood Frequency Graphs: Show Relationship Between

A
  • Recurrence interval
  • Peak discharge
107
Q

Lower-discharge floods: (flood graphs)

A
  • More frequent recurrence
  • Plot in graph’s lower left
108
Q

Higher-discharge floods:(flood graphs)

A
  • Less frequent recurrence
  • Plot in graph’s upper right
109
Q

Climate change will modify:

A
  • Recurrence intervals
  • Frequency curves
110
Q

National Weather Service (NWS) officials:

A
  • Track severe weather
  • Keeping public informed of potential flooding
111
Q

Flash flood watch:

A
  • Conditions may lead to flooding within 12–36 hours
112
Q

Flash flood warning:

A

Flooding has been detected.

113
Q

River flood warnings:

A
  • Issued when large rivers are expected to reach flood stage
114
Q

Predicted Flooding Risks Correlated

A

Minor: Low ground flooded, and low parts of
roads underwater; no internal house
flooding (maybe a few basements);
water over roads won’t stall vehicles

Moderate:Numerous buildings flooded; some
infrastructure affected; some people
need evacuation; water makes roads
impassable.

Major:Houses destroyed or floated off
foundations; infrastructure
destroyed; bridges washed away;
severe erosion; extensive
evacuations; National Guard
generally called in.

115
Q

Protecting Communities from Floods

A

 Sandbagging can reinforce and increase levee height.
* May increase flooding risk for downstream areas
 Additional efforts:
* Constructing diversion canals
* Restoring wetlands
* Passing laws that prohibit construction in floodways
 Adding sandbags to a levee to increase its height

116
Q

Private flood insurance is ______ available

A

rarely

117
Q

National Flood Insurance
Program:

A
  • Provided by the U.S. federal government
  • Premiums are expensive
118
Q

Federal buyout programs:

A
  • Purchasing flood-prone land for parks or wetlands
119
Q

Community wealth:

A
  • Poor communities often grow in flood-prone areas.
  • Building homes on stilts may be possible for some people.
120
Q

Floodway zoning ensures _____

A

minimal losses from a flood

1410 Chap 10 - 14 (5 decks)

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