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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
stream velocity
controlled by stream gradient (slope), channel shape and channel roughness; maximum velocity near center of channel
26
discharge
volume of water passing a | particular point in a stream over time (Q = W * D * V)
27
_______ stream velocities promote erosion | and transport of coarser sediments
higher; erosion of very small particles difficult due to | molecular binding forces
28
stream gradient
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
channel shape and roughness
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
hydraulic action
ability to pick up and | move rock and sediment
31
solution
dissolving of rocks
32
abrasion
grinding away of stream channel by the friction and impact of the sediment load
33
potholes
are eroded into streambed by the abrasive action of the sediment load in the stream
34
bed load
large or heavy particles that travel | on the streambed
35
traction load
large particles that travel along | the streambed by rolling, sliding or dragging
36
saltation load
medium particles that travel by | bouncing along
37
suspended load
small/light sediment that remains above the stream bottom by turbulent flow for an indefinite period of time
38
dissolved load
dissolved ions produced by chemical weathering of soluble minerals upstream
39
bars
ridges of sediment deposited in the | middle or along the sides of a stream
40
braided streams
contain sediment deposited as numerous bars around which water flows in highly interconnected rivulets
41
delta
``` 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
meandering streams
flow faster along the outside of bends and more slowly along the inside, depositing point bars on the insides of the meanders
43
meander cutoffs
may form when a new, shorter channel is cut through the narrow neck of a meander (as during a flood)
44
floodplains
are broad strips of land built up by sedimentation on either side of a stream channel
45
floodplain sediments
are left behind as flood waters slow and recede at the end of flood events
46
natural levees
main channel has slightly raised banks | with respect to the floodplain
47
downcutting
process of deepening a | valley by erosion of the streambed
48
v-shaped valleys
typically form from downcutting combined with mass wasting and sheet erosion
49
base level
the level which streams cannot erode below
50
graded streams
``` have concave-up longitudinal profile, lack rapids and waterfalls, represent a balance between available sediment load and transport capacity ```
51
lateral erosion
widens stream valleys by undercutting of stream banks and valley walls as stream swings from side to side across the valley floor
52
headward erosion
the slow uphill growth of a valley above its original source by gullying, mass wasting, and sheet erosion
53
stream terraces
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
incised meanders
``` retain sinuous pattern as they cut vertically downward; may be produced by profound base level changes, as when rapid tectonic uplift occurs ```
55
alluvial fan
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
flooding
Overbank flow condition, discharge | greater than channel’s holding capacity
57
stage
The height of the water level in a river at a | given location at a given time
58
hydrograph
Graphic representation of a river’s | discharge over time
59
lag time
The amount of time between the occurrence of peak rainfall and the onset of flooding
60
flash flood
local, sudden floods of large volume and short duration; typically triggered by heavy thunderstorms
61
recurrence interval
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
dams
designed to trap flood waters in reservoirs upstream and release it gradually over time
63
artificial levees
designed to increase capacity of river channel and works well until stream overtops levees, leading to extremely rapid flooding and erosion
64
wise land-use planning
including prevention of building within 100-year floodplains, is most effective
65
factors affecting flood damage
``` 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
adjustments to flood hazards
``` 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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