Unit 2 Rivers & Landslides Flashcards Preview

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Flashcards in Unit 2 Rivers & Landslides Deck (141):
1

Rivers feed into the _____

ocean

2

branch of river; stream that feeds into a larger stream

tributary

3

the line that separates neighbouring, smaller drainage basins

drainage basin divide

4

a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea

continental divide

5

What is the greatest/biggest drainage in the US?

Mississippi River

6

volume of water flowing past a point in the stream in a particular time interval

discharge

7

cfs

cubic feet per second

8

volume of sediment passing a point in the stream in a time interval

sediment load

9

Rivers appear to stay the same, because _____ and _____ occur at the same rate.

deposition; erosion

10

Rivers always carry as much _____ as they can.

sediment

11

If a river is carrying too little sediment, it will _____ until it has enough.

erode

12

If a river is carrying too much sediment, _____ will occur until it can carry the load.

deposition

13

How much sediment a river can carry depends on...

discharge, speed (gradient, roughness), size of available clasts

14

How are rivers shaped?

concave up

15

the size of a flood as measured in discharge that happens every 100 years

100 year flood

16

changes in rivers from headwaters to ocean

trends

17

If clast size decreases, the gradient will _______.

decrease

18

If the roughness decreases, the gradient will ____.

decrease

19

If sediment load increases, the river elevation will _____.

rise

20

If a river is lengthened, river elevation will ____.

rise

21

If we shorten a river, it will ____ river elevation.

raise/lower? Ask Dan.

22

steep gradients, v-shaped valleys, large clast sizes (to boulders), little or no floodplain, relatively low discharge

mountain streams

23

mountain streams

steep gradients, v-shaped valleys, large clast sizes (to boulders), little or no floodplain, relatively low discharge

24

many active streams, increased discharge, medium clast size (cobbles), wide and shallow, narrow floodplain

braided streams

25

braided streams

many active streams, increased discharge, medium clast size (cobbles), wide and shallow, narrow floodplain

26

meandering channel (looping back and forth), wide floodplain, clasts sand to mud, low gradient, deep and narrow (vs braided streams)

meandering streams

27

meandering streams

meandering channel (looping back and forth), wide floodplain, clasts sand to mud, low gradient, deep and narrow (vs braided streams)

28

outside bank of a water channel (stream), which is continually undergoing erosion; has vegetation

cut bank

29

depositional feature made of sand and gravel that accumulates on the inside bend of streams and rivers

point bar

30

meander channels that are cut off and abandoned

oxbow lakes

31

Lakes, over geologic time, fill up with mud/sediment and become ______ then ______.

meadows; forests

32

sand, silt, and clay deposits left by successive floods

levees

33

Levees make small floods ____ and big floods _____.

better; worse

34

form where sediment from streams enters calm water, balance the erosion of the drainage basin, have distributaries that deposit sediment in lobes

deltas

35

deltas

form where sediment from streams enters calm water, balance the erosion of the drainage basin, have distributaries that deposit sediment in lobes

36

Rivers try to take the ____ route to the ocean as long as they have a way to find it.

shortest

37

one river captures the entire flow of another and leaves the first high and dry

stream capture

38

high water event that results in a river overflowing its banks

flood

39

What causes rivers to flood?

intense rainfall (stationary thunderstorm, hurricane), prolonged rainfall (wet year), major snowmelt events (large snow pack or sudden thaw)

40

Individual flood events are _____, but they do follow _____ ______ _____.

unpredictable; regional climactic patterns

41

How often do rivers flood on average?

every 1.5 years

42

Flood size is measured in _____.

discharge

43

If discharge exceeds bank-full discharge, the river is in _____.

flood

44

the average length of time between floods of equal or greater magnitude

recurrence interval (RI)

45

buildings and pavements increase ____

runoff

46

development reduces ___ of floodplain

area

47

pavement reduces _____

infiltration

48

land use results in ____ flood levels and _____ duration

higher; longer

49

Cullowhee Creek was naturally a…

meandering stream

50

How can you tell the structure in Cullowhee Creek is man-made?

rocks are marble, rocks are too big for stream to carry; rocks are lined up too well

51

Why was the structure put in Cullowhee Creek?

diversify environment for animals (stream rehabilitation)

52

Does Cullowhee Creek have a levee? Why, or why not?

No, it hasn't flooded, because the creek is cut low in the channel and can't get out.

53

What evidence shows that Cullowhee Creek is a meandering stream?

small channel, wide floodplain

54

What evidence suggests that Cullowhee Creek is not a meandering stream?

too straight

55

What is the formula to find the RI?

R = N + 1 / m

56

In R = N + 1 / m, what does n represent?

years of data

57

In R = N + 1 / m, what does m represent?

rank of flood

58

What is a 5-year flood?

the magnitude (discharge) of a flood expected to occur, on average, every 5 years

59

A 5-year flood has a __% possibility of occurring on any given year.

20

60

What is the formula to determine the probability of a flood occurring on any given year?

probability = 1/RI

61

The 100-year flood has a __% chance of occurring in any given year.

1

62

There is a __% chance of a 100-year flood occurring in any 100-year period.

63.4

63

T/F: A 100-year flood occurs every 100 years like clockwork.

false

64

T/F: A 100-year flood lasts for 100 years.

false

65

a stream that branches off and flows away from a main stream channel

distributary

66

an area of land where surface water (from rain and melting snow or ice) converges to a single point at a lower elevation where the waters join another body of water

drainage basin

67

incline or slope

gradient

68

the rapid abandonment of a river channel and the formation of a new river channel; occur as a result of channel slopes that are much lower than the slope that the river could travel if it took a new course

lobe switching

69

sinking to the bottom, as a sediment

subsidence

70

the removal of water from solid material or soil by solid-liquid separation processes

dewatering

71

What is the relationship between sediment transport and river profiles?

to maintain homeostasis along the gradient, sediment-lacking rivers erode and sediment-heavy rivers deposit. the size of the rocks/clasts decreases from headwaters to ocean.

72

What is the effect of increased sediment?

deposition

73

What is the effect of dams?

erosion; hungry water

74

What is the effect of levees?

make small floods better; make big floods worse

75

What is the effect of channelization?

reduces biodiversity; stream more suitable for navigation; flood control; reduce natural erosion

76

Reducing the length of the channel by substituting straight cuts for a winding course

channelization

77

What is the effect of channel lengthening?

decreased gradient and sediment load capacity

78

How does gradient vary along the length of the river?

decreases

79

How does discharge vary along the length of the river?

increases due to tributaries

80

How does clast size vary along the length of the river?

decreases due to abrasion

81

How does roughness vary along the length of the river?

decreases due to clast size decreasing and discharge increasing

82

How does sediment load vary along the length of the river?

increasing due to tributaries

83

Why do rivers have concave up profiles?

If clast size decreases, the gradient will decrease. If the roughness decreases, the gradient will decrease. Discharge and sediment cancel out.
Deposition and erosion occur at the same rate along the river profile.

84

What are the flood risk effects of cutting off a bayou?

discharge increases

85

What are the flood risk effects of channelization?

low in channelized area; greater downstream

86

What are the flood risk effects of building levees?

small floods better; big floods worse

87

What are the flood risk effects of starving the floodplain of new sediment?

???

88

CC: How does channelization affect flooding?

the river is cut too far down into the channel to flood; it has never flooded

89

CC: How does channelization affect channel depth?

the channel is cut very deep

90

CC: How does channelization affect biodiversity?

reduces biodiversity but the man-made structure fixes that

91

CC: What is the goal of stream rehabilitation?

reinstate biodiversity

92

A: What are the hazards facing New Orleans?

water around New Orleans is rising, causing the city to sink further below sea level; the Mississippi's change in course would disconnect New Orleans's economy from inland commerce

93

A: What are the hazards facing Morgan City?

It uses the river to launch oil boats, barges, rigs, and the like offshore. With too much water, Morgan City would be unable to function

94

A: What is the purpose and history of the control structures?

reduce flooding, control river; in 1973 sank into whirlpool b/c foundations anchored into bedrock at least 7000 ft down, built on sediment

95

A: What is the general history of flood-control efforts along the Mississippi?

Great Flood of 1973, Army Corps of Engineers

96

A: What are the general effects of flood-control efforts along the Mississippi?

people argue over how much water they want when; Great Flood of 1973; constant battle with Atchafalaya

97

A: Describe the main problem posed by the Atchafalaya River. Explain why the Mississippi “wants” to change course and describe what the consequences would be throughout the region (especially for Baton Rouge, New Orleans, and Morgan City) if it did. Be specific about the consequences for each of these three locations. The consequences are not the same in every location.

The Atchafalaya takes in large amounts of water, growing bigger and bigger. It overtook the Red River this way. The only thing stopping it or slowing it down is Old River Control. Both the Atchafalaya and the Mississippi want the latter to change course, making the former the main stream. Rivers try to take the shortest route to the ocean, if they can find it. Right now, Old River Control is preventing the Mississippi from finding it. If it were to find the route, however, the consequences would be detrimental for New Orleans, Baton Rouge, and Morgan City. New Orleans is Louisiana’s largest city. This change in course would disconnect its economy from inland commerce. Between Baton Rouge and New Orleans, many large industries dependent upon the river’s navigational convenience and fresh water would suffer. The two cities could not survive on the creek that would remain. Morgan City’s issues are slightly different. It uses the river to launch oil boats, barges, rigs, and the like offshore. With too much water, Morgan City would be unable to function.

98

A: Has the Mississippi changed course in the past? When? How often? Why? Be specific.

The Mississippi River has always moved around inside a two hundred mile area. In 800 B.C., the channel shifted abruptly from the east and flowed that way for roughly a thousand years. In the second century A.D., it was captured and taken south by Bayou Lafourche. By 1000, that bayou was losing its control over the river’s present course through what is now the Plaquemines. By the 1950s, the Mississippi was ready to shift again and make the Atchafalaya its main stream. The Mississippi River appears to majorly change course every thousand years in order to reach the Gulf by the shortest and steepest gradient.

99

A: How have pavement, bayou closings, and channelization affected floods on the Mississippi? Be specific.

Every bit of pavement—in parking lots, on roads, everywhere—over half the United States encourages water runoff toward Louisiana. Bayou Manchac, the only eastern-flowing distributary, was dammed at the source in 1828. The pressure in the master stream increased. In 1868, a major distributary and natural escape for high spring waters called Bayou Plaquemine was sealed by an earthen dam at its junction with the Mississippi River. The river began to swell, running higher levels of discharge than ever before. In 1904, Bayou Lafourche, another major distributary, was dammed. Now, the first place water naturally escaped the Mississippi was Bayou Baptiste Collette, located sixty miles below New Orleans. By 1924, floodwaters increased an average of eight feet. Shreve created a channel out of a loop that nearly bent back on itself. It quickly became the main channel of the river with the Mississippi’s help. Shreve’s goal was to provide steamboats with a shorter, less tumultuous route. As a bonus, he sped up the Mississippi and lowered its crests in flood. Also, the creation of the channel advanced the impending date of the Atchafalaya’s capture of the Mississippi.

100

A: Why is New Orleans sinking? How have the levees affected this? Explain the processes involved.

The water around New Orleans is rising, causing the city to sink further below sea level. People have built levees all around the city to keep the water out. These levees sink in the wet ground and push mud and sediment out on either side. To solve this, people have built concrete floodwalls on top of the levees. This turns the city into a bowl, keeping water and silt locked inside. Swampy areas’ elevations rise. Three hundred and fifty-six thousand tons of sediment kept within mainline levees is shot into the Gulf every day. Water rises between levees, and the ground behind levees recedes.

101

A: Near the end of the essay, McPhee describes a barge in the Mississippi that was once left by the edge of the river, but is now 500 feet into the main channel. How did this happen? Describe the specific process responsible. Why is it relevant to his story? (Hint: the barge has not moved! Second hint: This is not the barge that was sunk at Morgan City.)

A sunken barge was left at the Mississippi riverbank twenty years before. The barge had not moved, but the Mississippi’s bank had been eroded by the water’s tremendous force in such a way that the barge now sat five hundred feet out in the river. The mention of this barge and the eroded bank reiterates the strength of the Mississippi River.

102

What controls the amount of friction?

roughness/stickiness; force of gravity into the slope

103

force of friction =

force into the slope x coefficient of friction (0-1)

104

coefficient of friction for most rocks

.6

105

coefficient of friction NASCAR tire

.8

106

coefficient of friction for normal tire

.65

107

What is the effect of slope angle?

increase force of gravity DOWN slope; decreases gravity INTO the slope (decreases friction)

108

Describe driving forces.

gravity (down the slope), weight, and slope angle; weight of initial slope material + weight of any structures built on the surface + steepening + weight of water or snow

109

holds rock together; rock sticks to itself

cohesion

110

List resisting forces.

friction and cohesion

111

pulling down slope

driving forces

112

keeps it from sliding

resisting forces

113

Shale and foliation planes are especially ____.

weak

114

Water is a ____.

lubrication

115

How are sliding surfaces usually shaped?

curved in unconsolidated or uniform material

116

The sliding surface is ____ at the top and ___ at the bottom. Therefore, driving forces are higher at the ___. Resisting forces are higher at the ___.

steeper; shallower; top; bottom

117

In a stable slope, humans often remove the toe for...

roads

118

In a stable slope, nature often removes the toe for...

meandering streams

119

In a stable slope, if A moves, so does B. B is the ___.

toe

120

way of inducing a slope to fail that's right on the edge of failure already

triggers

121

List triggers.

earthquakes, changes in slope angle or support, heavy rain events, rockfall

122

slurry of soil and weathered bedrock mixed with water that moves like a river; water is lubricating the flow not carrying the sediment

mudflows

123

like a mudlow but with large debris (up to house-sized); water is lubricating but not carrying the sediment

debris flows

124

particles move due to gravity, usually independent of each other; usually steep face

fall

125

coherent blocks of material move downslope, undeformed, along a discrete failure surface

slide

126

material deforms as it moves downslope

flow

127

a slow flow where expansion and contraction work with gravity to move material downslope

creep

128

slide vs. flow

slide- undeformed; flow- deformed

129

movement of material downslope by gravity

mass wasting

130

List types of mass wasting.

rock falls, rock slides, mud flows, debris flows, slumps, creeps

131

movement of rocks, sediments, or soil downhill as a coherent mass

landslides

132

What are the factors of a landslide?

weight and slope of the material (driving force); strength of the sliding surface (resisting force); shape of the sliding surface (affects both)

133

a cone-shaped deposit of sediment crossed and built up by a debris flow

debris fan

134

A bare rocky place on a mountainside or other steep slope

scar

135

landslide that occurs on a curved sliding surface (rotation)

slump

136

non-vegetated surface where land broke away

head scarp

137

boundary between rock that moved and rock that did not move

slip surface

138

bulging area at bottom of slump or landslide; undulating terrain

toe

139

The slow movement of rock debris and soil down a weathered slope.

creep

140

Give examples of evidence of creep.

curved tree trunk, tilted fence post, broken retaining wall, tension cracks

141

How can you prevent landslides?

limit infiltration, redirect surface water, support toe, unweight head