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GEO1009F > GEOMORPHOLOGY OF RUNNING WATAER > Flashcards

GEOMORPHOLOGY OF RUNNING WATAER Flashcards

1
Q

Most important agent of landscape formation

A

water

other factors may be locally dominant

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2
Q

distribution of earth’s water

A

fresh water = 3%

saline = 97%

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3
Q

distribution of fresh water

A

ice-caps and glaciers= 68.7%
ground water = 30.1%
other = 0.9%
surface water = 0.3%

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4
Q

distribution of surface water

A 
rivers = 2%
swamps = 11%
lakes = 87%
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5
Q

why does the total amount if water on earth’s surface stay constant?

A

due to processes associated with the hydrological cycle

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6
Q

what are the interconnected elements of the hydrological cycle?

A
  • precipitation
  • interception
  • evaporation
  • evapotranspiration
  • filtration/percolation
  • surface runoff
  • ground water
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7
Q

precipitation

A

clouds form due to ascent of saturated air parcel and associated cooling
Rain/snow results from coalescence of cloud water droplets.
Fog/mist is the same, except that the cooled air is found close to ground surface

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8
Q

spatial variation

A

Distribution and intensity of rain is highly variable, e.g. rain shadow; high spatial variability

areas in the rain shadow (it rains on one side of the mountain and the water cant pass to the other side of the mountain) are often very dry

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9
Q

spatial vaiability

A

means that some places get more rainfall than others

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10
Q

temporal variability

A

differences over time
short-term variab
seasonality
long term variab

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11
Q

intensity of precipitation

A

can also be variable

how much precip falls in a set amount of time??

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12
Q

intensity of precipitation

A

can also be variable

how much precip falls in a set amount of time??

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13
Q

precip variability in arid regions

A

lower precip
more variable precip
less reliable precip

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14
Q

interception

A
  • rain doesnt always fall directly on the grounf

- vegetation cover - precip is intercepted by plant foliage

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15
Q

geomorph importance of interception by foliage?

A

vegetation protects the land surface from direct impact of rainfall - reduces raindrop impact

vegetation also protects the soil through the binding action of plant roots

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16
Q

evaporation

A

-causes the huge difference between precip inputs and outputs along with transpiration (evap - storage and trans - comsumption)

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17
Q

evapotranspiration

A

accounts for 84% of precip in Africa

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18
Q

runoff ratio/ co-eff

A

ratio of total rainfall to total runoff in a catchment

low in semi arid seasonal rainfall climates such as across large areas of southern africa

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19
Q

Infiltration

A

depending on rainfall intensity and the nature of soil some precip enters soil by infiltration

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20
Q

what is infiltration capacity

A

maximum rate of absoption – if this is exceeded then surface water runoff happens

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21
Q

what factors influence infiltration capacity

A

soil conditions and land-use
-coarse vs fine grained soil
-heavy used land
less permeable surfaces - outcome may be erosion and transport of material

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22
Q

what happens to water that doesnt evap or runoff

A

infiltrates/percolates downwards to become groundwater

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23
Q

groundwater

A

precipitation that passes from soil later into underlying bedrock and meets zone of saturation (surface of which is referred to as the water table)

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24
Q

ground water variability

A

water table follows the general shape of surface topography

water table follows the general shape of surface topography

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25
Q

original ideas about runoff

A

American hydrologist: RE Horton

overland flow occurs on a slope in response to precipitation intensities that exceed infiltration capacity

26
Q

Hortonian overland flow

A

(infiltration excess overland) flow envisaged to occur across the landscapeand be main cause of the rapid rise of river levels during storms

27
Q

problems with hortonian flow model

A

1) surface runoff is rarely simultaneously widespread in the landscape
2) rainfall intensities do not always exceed infiltration capacity even during severe storms

28
Q

additional mechanism to explain how runoff occurs

A

saturation overland flow

29
Q

difference between hort and sat flow

A

hort = rainfall intensity is the initiating factor

sat = rainfall duration is the initiating factor

30
Q

interflow/through flow

A

lateral movement of water within soil that may produce pipes or even tunnels which transmit water at considerable speed

31
Q

movement of water on slopes is a combination of flow types

A

hortonian overland flow
saturation overland flow
through flow
ground water flow

ultimate destination - channel/river

32
Q

what is water measured as once in rivers?

A

discharge

the volume of water flowing through the stream per unit time

33
Q

extreme discharge -

A

flood

34
Q

changes in discharge over time are recorded on a …

A

flood hydrograph

35
Q

discharge formula

A

cross-sectional area x velocity

Q

36
Q

what is the flood hydrograph?

A

record of changes of discharge over time

37
Q

what causes variation is flood hydrograph shape

A

conditions in the catchment

38
Q

why do different surfaces have different infiltration capacities?

A

differences in interception (evaporation) and infiltration

39
Q

what to consider when looking at contrasting flood hydrogr

A

natural vegtation vs agricultural vs urbanisation

40
Q

different graphs flood hydros

A

size of drainage basin – small vs large

vegetation –
bare vs forest

valley side steepness –
steep vs gentle

soil type –
impermeable vs permeable

41
Q

what processes of water do geomorph work in channels

A

erosion
transport
deposition

42
Q

erosion

A

after weathering
running water erodes rock
–abrasion
–undercutting

stream ability to erose is dependent on type of flow

43
Q

types of stream flow

A

laminar

turbulent

44
Q

entrainment

A

once eroded material is transported in the direction of flow

45
Q

types of transport in a stream

A

in solution
suspended load
bedload

46
Q

saltation

A

jumping of particles

47
Q

bedload

A

carried along stream bottom

48
Q

suspended load

A

carried either in suspension or by saltation

49
Q

solution transport

A

sediment is dissolved in stream water and carried along steam in solution

50
Q

competence of a stream

A

ability of a stream to transport sediment

51
Q

what is stream competence dependent on

A

velocity of flow
volume of flow
periodicity of flow
periodicity of flow

52
Q

what results in deposition

A

loss of stream competence

53
Q

what causes loss in stream competence?

A

changes in discharge

change in gradient of river bed

54
Q

what does a Hjulstrom diagram depict?

A

relationship between erosion, transport and deposition

55
Q

zones of a drainage basin and dominant processes

A

erosion - headwaters
transport - middle reaches
deposition - lower reaches - floodplains and deltas

56
Q

what does the nature of relationship between particle size and velocity of flow determine

A

whether a particle will be eroded, transported or deposited

57
Q

Hjulstrom diagram parameters

A

x axis = grain size
y ax = stream velocity
headings top x axis - fine particles - coarser particles

58
Q

why is a greater velocity needed for fine particles?

A

clump together and form a relatively large mass

59
Q

what are three human processes that impact the environment (fluvial systems)

A

land use changes
urbanization
dam construction

60
Q

what are the impacts on fluvial systems by three human processes

A

hydrolog cycle is modified

  • -discharge
  • -channel form
  • -sediment load
61
Q

changes in streams following landuse changes…

A

in annual and seasonal discharge (may be positive or negative) e.g. in fynbos catchments the effect of a change from fynbos to forest plantation (increased biomass) is to reduce runoff

–flood characteristics (increases or decreases)

–water quality e.g. fertilizers

– erosion (increases)

62
Q

effects of dam construction (check written notes for better explanation)

A

Decreased sediment load downstream of the impoundment results in ‘clearwater erosion’ (i.e. incision of stream below dam wall due to increased competence)

Decreased sediment supply to the coast impacts beach and dune systems (sediment ‘starvation’)

Shrinking deltas and accelerated relative sea level rise

Mass of water as well as increased pore water pressures in underlying geology may increase risk of slope failure (e.g. Vaiont, Chinese examples)

GEO1009F (16 decks)

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