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Geology 120 > Streams and Floods (Ch 10) > Flashcards

Streams and Floods (Ch 10) Flashcards

1
Q

Running Water

A

the most important geologic agent in eroding,

transporting and depositing sediment

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2
Q

Hydrologic Cycle

A

the movement and
interchange of water between the sea, air, and
land

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3
Q

evaporation

A

solar radiation provides energy

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4
Q

precipitation

A

rain or snow

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5
Q

transpiration

A

evaporation from plants

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6
Q

runoff

A

water flowing over land surface

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7
Q

infilitration

A

water soaking into the ground

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8
Q

Stream

A

a body of running water, confined to
a channel, that runs downhill under the
influence of gravity

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9
Q

headwaters

A

upper part of stream near its

source in the mountains

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10
Q

mouth

A

place where a stream enters sea,

lake or larger stream

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11
Q

channel

A

a long, narrow depression eroded

by a stream into rock or sediment

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12
Q

stream banks

A

sides of channel

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13
Q

streambed

A

bottom of the channel

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14
Q

floodplain

A

flat valley floor composed of

sediment deposited by the stream

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15
Q

drainage basin

A

the total area

drained by a stream and its tributaries

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16
Q

tributary

A

a small stream

flowing into a larger one

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17
Q

divide

A

ridge or high ground that
divides one drainage basin from
another

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18
Q

continental divide

A

separates
the streams that flow into the
Pacific from those that flow into
the Atlantic and Gulf of Mexico

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19
Q

drainage pattern

A

the arrangement, in map
view, of a stream and its tributaries; most tributaries join the main stream at an acute
angle, forming a V or Y pointing downstream

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20
Q

dendritic

A

drainage pattern resembling the branches

of a tree

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21
Q

radial pattern

A

streams diverge outward like the

spokes of a wheel, such as on conical mountains

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22
Q

rectangular pattern

A

tributaries have frequent 90°

bends and join other streams at right angles

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23
Q

trellis pattern

A

parallel streams with short tributaries

meeting at right angles

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24
Q

stream erosion

A

Controlled by flow velocity and discharge

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25
Q

stream velocity

A

controlled by stream
gradient (slope), channel shape and channel
roughness; maximum velocity near center
of channel

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26
Q

discharge

A

volume of water passing a

particular point in a stream over time (Q = W * D * V)

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27
Q

_______ stream velocities promote erosion

and transport of coarser sediments

A

higher; erosion of very small particles difficult due to

molecular binding forces

28
Q

stream gradient

A

the downhill slope of the
streambed; typically measured in feet/mile in the U.S., and in
meters/kilometer elsewhere, and usually decreases downstream

29
Q

channel shape and roughness

A

effect stream velocity due to drag, narrower, deeper channels allow faster flow, smoother channels allow faster flow, wider, shallower channels decrease flow speed, and rougher channels decrease flow speed

30
Q

hydraulic action

A

ability to pick up and

move rock and sediment

31
Q

solution

A

dissolving of rocks

32
Q

abrasion

A

grinding away of stream channel
by the friction and impact of the sediment
load

33
Q

potholes

A

are eroded into streambed by the
abrasive action of the sediment load in the
stream

34
Q

bed load

A

large or heavy particles that travel

on the streambed

35
Q

traction load

A

large particles that travel along

the streambed by rolling, sliding or dragging

36
Q

saltation load

A

medium particles that travel by

bouncing along

37
Q

suspended load

A

small/light sediment that
remains above the stream bottom by turbulent
flow for an indefinite period of time

38
Q

dissolved load

A

dissolved ions produced by
chemical weathering of soluble minerals
upstream

39
Q

bars

A

ridges of sediment deposited in the

middle or along the sides of a stream

40
Q

braided streams

A

contain sediment
deposited as numerous bars around
which water flows in highly
interconnected rivulets

41
Q

delta

A 
body of sediment deposited at
the mouth of a river when flow velocity
decreases; surface marked by shifting
distributary channels; shape of a delta depends on whether
its wave-dominated, tidedominated,
or stream-dominated
42
Q

meandering streams

A

flow faster along
the outside of bends and more slowly along
the inside, depositing point bars on the
insides of the meanders

43
Q

meander cutoffs

A

may form when a new,
shorter channel is cut through the narrow
neck of a meander (as during a flood)

44
Q

floodplains

A

are broad strips of land built
up by sedimentation on either side of a
stream channel

45
Q

floodplain sediments

A

are left behind as
flood waters slow and recede at the end of
flood events

46
Q

natural levees

A

main channel has slightly raised banks

with respect to the floodplain

47
Q

downcutting

A

process of deepening a

valley by erosion of the streambed

48
Q

v-shaped valleys

A

typically form
from downcutting combined with
mass wasting and sheet erosion

49
Q

base level

A

the level which streams cannot erode below

50
Q

graded streams

A 
have concave-up
longitudinal profile, lack rapids and
waterfalls, represent a balance between
available sediment load and transport
capacity
51
Q

lateral erosion

A

widens stream valleys
by undercutting of stream banks and valley
walls as stream swings from side to side
across the valley floor

52
Q

headward erosion

A

the slow uphill
growth of a valley above its original source
by gullying, mass wasting, and sheet erosion

53
Q

stream terraces

A

step-like landforms
found above a stream and its floodplain; occurs when river rapidly cuts
downward into its own floodplain, represents relatively sudden change
from deposition to erosion, and can be caused by rapid uplift, drops
in base level, or climate changes

54
Q

incised meanders

A 
retain sinuous pattern as
they cut vertically
downward; may be produced by
profound base level
changes, as when rapid
tectonic uplift occurs
55
Q

alluvial fan

A

large, fan- or cone-shaped pile of sediment that
forms where stream velocity decreases as it emerges from a
narrow mountain canyon onto a flat plain; well-developed in desert regions, such as the southwestern U.S., and larger fans show grading from large sediments nearest the
mountains to finer sediments farther away

56
Q

flooding

A

Overbank flow condition, discharge

greater than channel’s holding capacity

57
Q

stage

A

The height of the water level in a river at a

given location at a given time

58
Q

hydrograph

A

Graphic representation of a river’s

discharge over time

59
Q

lag time

A

The amount of time between the
occurrence of peak rainfall and the onset of
flooding

60
Q

flash flood

A

local, sudden floods of large
volume and short duration; typically triggered by heavy
thunderstorms

61
Q

recurrence interval

A

R = (N + 1)/M
N as the number of years of record, M is the rank
of individual flow within the recorded years; The probability of a given magnitude flood
P = 1/R; Statistical probability versus reality
Probability: One 25-year flood, on average, once
every 25 years
Reality: Two 25-year floods within the same year

62
Q

dams

A

designed to trap flood waters in
reservoirs upstream and release it
gradually over time

63
Q

artificial levees

A

designed to increase
capacity of river channel and works well
until stream overtops levees, leading to
extremely rapid flooding and erosion

64
Q

wise land-use planning

A

including
prevention of building within 100-year
floodplains, is most effective

65
Q

factors affecting flood damage

A 
Regional land-use changes, such as urban
development, deforestation, soil erosion, etc.
Land use on the floodplain
Frequency and magnitude of flooding
Lag time and duration of flooding
Sediment load
Effectiveness of forecasting, warning, and
emergency management
66
Q

adjustments to flood hazards

A 
The structural approach:
-Engineering barriers: Levee augmentation
-Channelization
-River-channel restoration
Flood insurance
Flood-proofing
Floodplain regulation: Obtaining the most
beneficial use of floodplains
-Flood-hazard mapping
-Floodplain zoning

Geology 120 (5 decks)

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