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EAS 205 > flooding and streams! > Flashcards

flooding and streams! Flashcards

1
Q

what is the hydrosphere?

A

all water at or near the surface of the earth

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2
Q

what steps are in the hydrologic cycle

A

evaporation
condensation
precipitation
runoff
infiltration
percolation

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3
Q

what is the largest river?

A

amazon! 175,000 meters cubed per second water flow

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4
Q

what is a stream?

A

a body of water confined to a channel

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5
Q

what is a river?

A

major branches of a stream system

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6
Q

what is a drainage basin

A

region from which a stream draws its water supply
isolates water
the size of a stream is related in part to the size of the drainage basin, which determines how much water can flow into the stream

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7
Q

what is the drainage basin defined by?

A

topographically determined divides

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8
Q

what is stream discharge?

A

volume of water that passes a given point in a given time through a channel of a certain width and depth

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9
Q

how would you calculate discharge?

A

multiple cross-sectional area (width x depth) by velocity of the flow (distance/time)

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10
Q

what will change the shape of the stream / land?

A

faster moving water

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11
Q

what is laminar flow?

A

straight or gently curved streamlines run parallel to one another without mixing (slow moving rivers)

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12
Q

what is turbulent flow?

A

streams mix, forming eddies (fast flowing rivers)

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13
Q

what is a streams capacity?

A

total sediment load carried by a stream

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14
Q

what is a streams competence?

A

ability to carry material of a given size

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15
Q

how are capacity and discharge related?

A

the faster the stream flows, more water present, more material moved, larger material moved

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16
Q

what does stream velocity impact?

A

sediment sorting
- slow moving water: fine-grain
- swift currents: wider range of grain

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17
Q

what is a graded stream?

A

various factors combine to yield an average of neither erosion or sedimentation over the course of the stream
at equilibrium!
low spots filled in, high spot sediment grabbed

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18
Q

what can effect the equilibrium of sediment transport?

A

discharge, base level, tectonics, resistance of weathering, human intervention

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19
Q

what is a streams gradient?

A

velocity of stream largely dependent on steepness of the stream
gradient decreases as the stream approaches its baselevel

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20
Q

what is the base level of a stream?

A

lowest elevation to which a stream can flow

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21
Q

longitudinal stream profile

A

approaching base level (potentially sea level)
slide shaped line on graph

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22
Q

a change in the base level disrupts?

A

equilibrium! tries to go back

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23
Q

steps of changes to a graded stream

A
  1. normal stream profile
  2. change in bas level changes profile
  3. erosion moves material toward sea level. sediment moving to river delta is deposited in lake. previous delta (where sediment is deposited) abandoned
  4. eventually stream profile restored
24
Q

how can humans change base level?

A

by building a dam, which also changes longitudinal profiles

25
Q

what are the two major stream types?

A

meandering and braided

26
Q

what is a meandering stream?

A

gentle gradients, generally erode unconsolitaed sediment and weak bedrock. carry fine sediment, path may shift significantly with erosion and deposition

edmonton! straight line

27
Q

what is a braided stream?

A

many channels which diverge and merge, steep gradients, high sediment loads, variations in discharge

jasper / banff !

28
Q

how is a braided stream created?

A

high velocity / high sediment streams flow over nearly flat, easily eroded terrain, the fast-moving sediment-laden water cuts across soft sediments at the end of existing channels

29
Q

what is a point bar?

A

a place where sediment is left behind

30
Q

how are meandering streams formed?

A

shift from side to side in a snaking motion
current is faster on outside banks: erode
current is slower on the inside banks: deposited (forms point bar)

31
Q

where do you want to build you house?

A

point bar!

32
Q

how is a floodplain formed?

A

deposit and erosion in meandering streams

33
Q

what are natural levees?

A

ridges of course material that confine the stream within its banks between floods

34
Q

how are natural levees formed?

A

before flood: sediment deposit by flooding of stream channel build up low levees
after flood: water leaves channel, rapidly lose velocity, drop sediment along channel borders

35
Q

what is a hydrograph

A

a plot of steam discharge at a point over time
- records fluctuations in discharge or stream height over time
- discharge / stage on vertical axis; time on horizontal axis

36
Q

when the _____ exceeds the _______, a flood is caused

A

input; output

37
Q

what are the factors that can cause flooding?

A

excessive rainfall
snowmelt in mountains
severe storms
hazardous blockage of stream channel (trees, rock avalanches)

38
Q

what are the characteristics of a flood?

A

stage and crest

39
Q

what is a stage

A

elevation / height of the water

40
Q

what is a crest?

A

maximum stage reached (bulge of water coming downstream)

41
Q

where do upstream floods occur?

A

small, localized upper part of a basin

42
Q

where do downstream floods occur?

A

larger, lower part of a drainage basin

43
Q

what is a flash flood?

A

upstream flood characterized by a rapid rise of steam stage

44
Q

what events cause upstream floods?

A

locally intense rainstorms or dam bursts (flash floods)

45
Q

what events cause downstream floods?

A

heavy rain or snowmelts

46
Q

what would a hydrograph look like for an upstream flood?

A

sharp peak, short duration

47
Q

what would a hydrograph look like for an downstream flood?

A

lower peaks, broader duration

48
Q

what is the rate of surface runoff influenced by?

A
  1. ground cover: different rates in infiltration in soils, rocks and manmade structures
  2. topography: steepness of terrain governs how much is infiltrated into soil vs surface runoff
    3.presence of vegetation: plants may provide physical barrier +increase soil infiltration (absorb water)
  3. climate: determines level of rainfall and periodicity of storms
49
Q

how to calculate the flood frequency to plot curve?

A

R = (N+1)/M

R: recurrence
N: years
M: annual maximum

50
Q

reasons why people live in floodplain

A

ignorance of hazards + inexpensive land that is often beuatiful

51
Q

what impact does climate change have on floods?

A

faster hydrological cycle = more frequent floods
plus raise in sea level

52
Q

what are some flood hazard reduction strategies?

A

restrictive zoning
retention pond
diversion channel
channelization
levees
flood control dams and reservoirs
do not build in a floodplain

53
Q

how do levees prevent flooding?

A

allowing waters to reach higher stage without spilling onto the floodplain. sometimes artificially enlarged or constructed to constrict flooding

54
Q

what are flood control dams?

A

retain excess runoff and release in a controlled manner to not overwhelm the stream

55
Q

what was the worlds most catastrophic flood?

A

breaching of the ice dams and retreating of continental ice sheets

EAS 205 (17 decks)

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