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Geohazard Finals > Flooding > Flashcards

Flooding Flashcards

1
Q

The basic role of streams and rivers (larger streams) within the Earth system

A

to drain water off the landscape and to transport sediment

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2
Q

When a bank’s ability to carry water is overwhelmed by the
sheer volume of water flowing off the landscape, what happens?

A

Flood

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3
Q

True or False: humans tend to concentrate their settlements along waterways.

A

True

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4
Q

Described as the volume of water moving through a channel over a given time interval, commonly measured in units such as cubic feet per second (ft3/s)

A

Stream Discharge

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5
Q

a process where water flows through stream channels

A

Discharge

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6
Q

discharge of groundwater into the surface environment; fairly continuous unlike the sporadic input of water to a stream and groundwater may travel anywhere from a few days to thousands of years before discharging into a stream channel

A

Groundwater baseflow

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7
Q

What processes allows water to return back to the atmosphere?

A

Evaporation and plant transpiration

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8
Q

They provide information about a river or stream by simply plotting the discharge versus time.

A

Stream hydrographs

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9
Q

The amount of time for water to move across the landscape and into channels; will vary depending on the distance between where the rain is falling and the particular channel where discharge is being measured.

A

Lag time

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10
Q

Continuous input of groundwater baseflow allows streams in many areas to keep flowing at some minimum level. This contribution of groundwater baseflow keeps streams from going dry between rain events, thus is critical in maintaining the health of stream ecosystems.

A

Baseflow conditions

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11
Q

High precipitation allows more water to infiltrate to the water table which causes the water table in humid regions to be higher than the streams channel, thereby forcing groundwater to flow into streams. Such streams are often referred as

A

Gaining streams

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12
Q

are a result of less deep infiltration in arid areas resulting in a water table that is below the level of most stream channels. Under these conditions, the water in the stream will flow into the groundwater system.

A

Losing streams

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13
Q

is a network of stream channels where merging tributaries (smaller of any two merging channels) form progressively larger streams

A

Drainage System

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14
Q

The term _____ is often applied to the larger stream that
serves as the principal channel within a drainage system

A

River

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15
Q

The upper portion of the drainage system

A

Headwaters

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16
Q

found in the lower part of the system where a river empties into an ocean, lake, or another river

A

Mouth

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17
Q

True or False: Headwater streams are generally large and relatively slow, moving and occupy narrow valleys, but then evolve
toward the mouth into gently flowing rivers that occupy wider valleys.

A

False, they are generally small and relatively fast.

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18
Q

Individual systems are separated from one another by a topographic high or crest in the landscape called

A

Drainage Divide

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19
Q

Also known as a watershed

A

Drainage basin

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20
Q

What is the largest river in the world in terms of discharge?

A

Amazon river (7.8 million cubic feet per second)

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21
Q

All of the water within this basin will drain down to a
stream then flow out of the basin

A

Drainage basin

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22
Q

True or false: drainage basins are categorized by their size.

A

False, size does not matter

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23
Q

are any smaller streams that feed larger streams within a
drainage basin

A

Tributaries

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24
Q

A method of classifying or ordering the hierarchy of natural channels

A

Strahler Stream Order

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25
Q

It reflects downstream trade off between discharge and slope in setting transport capacity (and thus ability to move sediment and incise rock).

A

Stream Longitudinal Profile

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26
Q

The level below which a river or stream cannot incise. It is the limiting level below which a stream cannot erode the land.

A

Base level

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27
Q

The ultimate (or absolute) base level for most streams

A

Global sea level

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28
Q

approximately equals the inverse of the source basin length

A

Drainage density

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29
Q

The formula for drainage density

A

D = L/A

D = Drainage Density
L = Total stream channel length
A = Area of the Drainage Basin

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30
Q

Steep terrain tends to be highly dissected and thus have

A

High drainage density

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31
Q

Gentle terrain tends to be less well dissected, with substantial hillslope convexities and has

A

Low drainage density

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32
Q

An example of high drainage density but small source areas

A

Mancos Shale Badlands, Utah
Rill field, Mt. Pinatubo, Philippines

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33
Q

common on gently sloping convex

A

Low drainage density, large source areas-

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34
Q

Types of drainage patterns

A

 Dendritic
 Parallel
 Trellis
 Rectangular
 Radial
 Annular
 Multibasinal
 Contorted

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35
Q

Most commonly formed on horizontally bedded and uniform sediments or on uniformly resistant crystalline rocks.

A

Dendritic drainage pattern

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36
Q

Usually develops on moderate to steep slopes, but also where regional structure, such as outcropping resistant rock bands, are elongated and parallel. All forms of transition can occur this type and dendritic and trellis pattern.

A

Parallel drainage pattern

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37
Q

Patterns most commonly on dipping or folded sedimentary or weakly metamorphosed sedimentary rocks; also areas of joints and faults which intersect with right angles and old sand dunes with parallel alignment

A

Trellis drainage pattern

38
Q

Usually have a more or less perpendicular turns mainly
caused by criss-crossing fractures.

A

Rectangular drainage pattern

39
Q

Occurs around domes or cones, and particularly common on
volcanic areas.

A

Radial drainage pattern

40
Q

Patterns also develop around domes, where there exists alternating resistant and weak beds, so that the major channels cut through the strike and the low order streams follow the dip of the rocks.

A

Annular drainage pattern

41
Q

Can occur in a variety of conditions where local hummocks and depressions inhibit a continuous channel network. Irregular glacial deposits or erosional hollows due to solution of underlying lithology, irregular thawing permafrost. Coastal dunes, delta plains, and wind eroded hollows

A

Multibasinal drainage pattern

42
Q

Incised into rocks with complicated structural patterns. Associated with crystalline metamorphic rocks with a history of intense folding, jointing, intrusions, alterations, and faulting.

A

Contorted drainage pattern

43
Q

Checkpoint: Types of streams can be divided and subdivided according to:

A

 Whether they are water-holding or not, (perennial, intermittent, & ephemeral)

 Linear form of the river, i.e. straight, meandering, & braiding

 Cross-profile or “transverse” section of the river, i.e., a gently or steeply sloping channel form. They can be either smooth or irregular in shape

 The length-profile or “longitudinal” section of the river, i.e., a graded or interrupted profile, with waterfalls and lakes

 The genesis or evolution of the river caused by bedrock structure, main geologic structure and riverbed stability

44
Q

are loose rock particles/sediments deposited on a stream

A

Alluvium

45
Q

One of the key factors in a stream’s ability to erode the landscape is the

A

velocity of the water

46
Q

When water enters a meander bend it is forced to (A)_________ on the inner part of the bend, but (B)_________ on the outer part.

A

(A) slow down, (B) speed up

47
Q

are unstable overhang located at the outer bank which is produced by the velocity increase on the outer bank which subsequently enhances the ability of the water to cut (erode) into the bank.

A

Cutbanks

48
Q

On the inner bank where velocity decreases, sediment tends to accumulate and form a deposit known as a

A

Point bar

49
Q

What is the primary cause of erosion and undercutting on the outer bank of a bend in a stream channel, leading to the formation of an unstable overhang that eventually collapses?

A

Increased water velocity on the outer bank of the bend

50
Q

is the vertical erosion of a river or stream channel, resulting in the deepening of the channel over time

A

Downcutting

51
Q

Downcutting by streams is not performed by the water itself, but rather by the sediment that physically scrapes or wears away rock in a process called

A

Abrasion

52
Q

These form during periods of high stream discharge when the water column develops a swirling motion called an eddy current.

A

Potholes

53
Q

The velocity of a particular stream segment is controlled
by the steepness of the channel, called the

A

Stream gradient

54
Q

used to describe the lowest level to which a stream can erode

A

Base level

55
Q

is often referred to as ultimate base level

A

Sea level

56
Q

forms when the ability of a river flow to cut downward is reduced by a resistance rock body, lake, or inland sea.

A

Temporary base level

57
Q

The ability of running water to transport and deposit sediment is dependent on both the water velocity and the types of particles being transported.

A

Stream Transport and Deposition

58
Q

describes the fraction of solid particles that is in a suspended state and moving at the same velocity as the water— suspended material is what makes streams appear muddy.

A

Suspended load

59
Q

Consists of sediment particles that roll, bounce, or remain stationary on the streambed.

A

Bed load

60
Q

The _____ particles to be removed from the bed load are the
smallest, least dense, and most angular.

A. First
B. Last

A

A. First

61
Q

The process whereby water separates sediment grains based on their size, shape, and density is called

A

Hydraulic Sorting

62
Q

The combination of hydraulic sorting and chemical
weathering eventually produces relatively pure deposits of ________________

A

Sand and Clay

63
Q

are mound-shaped channel deposits consisting of sorted material ranging in size from boulders to coarse gravel to fine sand

A

Bars

64
Q

Boulder deposits are generally found where?

A

near the headwaters of a drainage system

65
Q

Crescent-shaped bars, called point bars, develop on the ______ of meander bends where water velocity decreases.

A

Inside

66
Q

formed when a river enters a lake or ocean and splits into smaller channels and begins to deposit sediment due to a decrease in velocity

A

Delta

67
Q

are large fan-shaped deposits that form where steep mountain streams empty out onto valley floors at the mouth of rivers

A

Alluvial fans

68
Q

Streams also transport considerable amounts of dissolved ions (charged atoms) in what scientists refer to as

A

Dissolved load

69
Q

The erosion that occurs along the outside of meander bends produces wider valleys over time, whereas deposition on the inner banks helps to build a flat plain on the valley floor called a

A

Natural floodplain

70
Q

When rivers overflow their banks, the first area to be inundated is
what portion of the valley?

A

The flat portion of the valley.

71
Q

What is the floodplain’s primary role?

A

to periodically store large volumes of water moving through a drainage basin

72
Q

are pair of ridges that run parallel to the bank which are formed due to the deposition of sediment, commonly sand, at the edge of the bank

A

Natural Levees

73
Q

are areas on the floodplain that are poorly drained and can remain wet long after a flood

A

Backswamps

74
Q

are old floodplain left high and dry as river migrates

A

Stream terraces

75
Q

True or False: Well-defined terraces often develop in response to relatively rapid changes in base level resulting from tectonic uplift or lowering of sea level.

A

True

76
Q

Natural levees are typically found along river channels that have ___________ floodplains.

A

Well-defined floodplains

77
Q

Meanders tend to grow as the flow erodes the banks, favoring
development of _________________.

A

Meandering Channels

78
Q

Scientists use ________________ and __________ to compare floods in a quantitative manner.

A

Stream discharge and height

79
Q

is the height at which a river begins to overflow its banks.

A

Flood Stage

80
Q

computed by multiplying the cross-sectional area of a river by its water velocity

A

Discharge

81
Q

Floods are particularly difficult to predict because they are

A

dependent on specific weather events

82
Q

represents the frequency a particular discharge value can be expected to repeat itself. It tells us how often we can expect floods of a certain size.

A

recurrence interval

83
Q

Another useful way of measuring flood frequency is _____________, which is simply the inverse or reciprocal of the recurrence interval (1/RI).

A

Percent probability

84
Q

The reliability of recurrence intervals is dependent on the availability of __________________________.

A

historical discharge records

85
Q

The potential for flooding in a given area naturally increases as the _________ and __________ of rainfall increases.

A

intensity and duration

86
Q

The ability of the ground to absorb water is referred to as

A

infiltration capacity

87
Q

are floods that have short duration with relatively high peak discharge; small streams and rivers tend to rapidly overflow their banks.

A

Flash Floods

88
Q

can be defined as one where a river leaves its channel farther down in its drainage basin, flowing out onto its floodplain and inundating large areas of the valley floor. They are caused by regional accumulations of water higher up in the drainage basin.

A

Downstream floods

89
Q

Land-Use Factors that Affect Flooding

A
  1. Removal of natural vegetation
  2. Destruction of Wetlands
  3. Construction Activity
  4. Urbanization
90
Q

A phenomenon where excessive dislodged sediment is moved off the landscape into drainage systems which causes channels to become filled with sediment

A

Sediment pollution

91
Q

Flood Mitigation Measures

A

 Dams
 Artificial Levees
 Channelization
 Retention Basins
 Erosion Controls
 Flood Proofing
 Flood Plain Management
 Education

Geohazard Finals (3 decks)

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