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Geology > (10) + (11) The Hydrologic Cycle T3 > Flashcards

(10) + (11) The Hydrologic Cycle T3 Flashcards

1
Q

World’s Water Distribution

A
  • Oceans: 97%
  • Glaciers & other ice: 2%
  • Ground water: 0.6%
  • Lakes, freshwater: 0.01%
  • Lakes, saline: 0.01%
  • Soil Moisture: 0.005%
  • Atmosphere: 0.001%
  • Rivers: 0.0001%
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2
Q

Fresh water usage

A

In Canada, average self-contained household used 400-1500 liters of water per person per day

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3
Q

Stream and Flood Erosion

A
  • Surficial process
  • Running water:
    o Major geologic agent on earth for erosion transportation and deposition of sediment and landscape development
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4
Q

Why are streams important?

A 
- Role in hydrologic cycle
o	Carry most of water that goes from land to sea
- Transport sediment
o	Billions of tons per year (~20 billion tons/year)
o	Sediment can be preserved as rock
- Transport dissolved salts to ocean
o	Products of weathering
o	Role in saltiness of seawater
- Shape major landforms on earth
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5
Q

Stream

A
  • Body of running water
  • Confined in a channel
  • Moves downhill (gravity)
  • Drain the land surface
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6
Q

Parts of stream

A
  • Headwaters (top of mountain)
  • Mouth (to the sea)
  • Channel
  • Bed stream banks
  • Flood plain (places where the stream used to be)
  • Valley wall (on either side of the flood plain)
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7
Q

Sheet Wash

A
  • Thin layer (few mm) of unchanneled water flowing downhill
  • Ground becomes saturated – water flows overland
  • Between mass wasting and stream erosion
  • Common in deserts
  • Common in humid areas with heavy thunderstorms
  • Driven by gravity
  • Promoted erosion once its moving
  • And leads to development of stream channels (downcutting)
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8
Q

Stream Valleys: Formed by…

A
  • Downcutting by streams

- Mass wasting and sheetflow down banks/ valley walls

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9
Q

How does a river expand its own valley?

A
  • Eroded rock and sediment
    o Deepens channel (downcutting)
    o Widens channel (meanders; lateral erosion makes a flood plain)
    o Lengthens channel (headward erosion and deposition at mouth)
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10
Q

Drainage patterns

A
  • Arrangement in a map view of a river and its tributaries
  • Tributaries join a main stream forming a V (or Y) that points downstream
  • Reflect nature and structure of underlying rocks
  • Stream drainage patters
    o Dendritic
    o Rectangular
    o Radial
    o Trellis
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11
Q

Dendritic drainage pattern

A
  • Most common
  • Uniformly erodible rock
  • ‘Tree-like’ appearance to pattern
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12
Q

Radial drainage pattern

A
  • Looks like spokes on a wheel

- Form on high conical mountains

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13
Q

Rectangular drainage pattern

A
  • Develop on jointed rock (rocks that breaks and fractures in a rectangular pattern)
  • Right angle bends
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14
Q

Trellis drainage pattern

A
  • Layers of resistant rock alternate with layers of nonresistant rock (water flows between resistant rock)
  • Parallel main streams
  • Short tributaries, near right angles
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15
Q

Drainage basins, tributary, and divide definition

A
  • DB: Total area drained by a stream and its tributaries
  • T: small stream flowing into a larger one
  • Divide: ridge or strip of high ground dividing one drainage basin from another
    o ‘Continental divide’ – Pacific Ocean/ Atlantic Ocean
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16
Q

Rivers energy used for

A
  • Carry sediment (erode, transport, deposit)
  • Overcome resistance to flow (changes in the channel shape, roughness, and length)
    o Changing one of these will affect the other
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17
Q

Velocity

A
  • Distance per unit time
  • Moderately fast river: 5km/h
  • High velocity leads to erosion and transportation of sediment
  • Low velocity leads to sediment deposition
  • Velocity varies
    o Water travels at different speeds within the stream
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18
Q

What affects velocity?

A
  • Gradient (slope)
  • Channel shape (deep narrow (faster) vs shallow wide (slow))
  • Channel roughness (creates friction and turbulence)
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19
Q

Max velocity of stream location

A
  • Near middle

- Curved stream: toward outside of curve

20
Q

Discharge

A
  • Volume of water that flows past a given point in a unit of time
  • Discharge increases downstream
    o Tributaries join, adding more water
    o Water flows out of the ground into the river through the stream
  • But in dry climates discharge decreases
21
Q

What else affects discharge?

A 
- Human activity
o	Diversions
o	Irrigation
- Floods
- Seasonal variation
22
Q

Stream Erosion

A
  • Streams usually erode the rock and sediment over which it flows
  • Results in characteristic “v-shaped” valley profile
23
Q

Stream erosion involves processes of

A
  • Hydraulic action
  • Solution
  • Abrasion
24
Q

Streams are turbulent

A
  • Their waters flow in a complex fashion
25
Q

Hydraulic action

A
  • Ability of flowing water to pick up and move rock and sediment
26
Q

Solution

A
  • Dissolving rock in water
  • Slow but can be very effective
  • Limestone: karst topography (caves)
27
Q

Abrasion

A
  • Grinding away by friction and impact
  • Usually most effective erosion process on a stream bed
  • The more sediment a stream carries, the faster it is likely to wear away its bed
  • Coarse sediment most effective
  • Can leave a pothole (depression) after eroded (from swirling)
28
Q

Sediment transported as…

A
  • Bed load (sand and gravel, on the bottom and middle) (only this, water clear)
    o Large heavy sediment that travels in stream bed
    o Traction – rolling, sliding, and dragging
    o Saltation – bouncing
  • ** Suspended load (on the top) (gives colour)
    o Sediment carried along by water turbulence – doesn’t settle
  • ** Dissolved load (in the suspended load)
    o Products of chemical weathering
29
Q

Water can be polluted..

A

with or without sediment

30
Q

What is stream deposition and its types?

A
  • Reflects a drop in velocity (loses energy)
  • Along stream can form
    o Bars
    o Braided streams
    o Flood plains
  • At or near end of stream
    o Delta
    o Alluvial fan
  • Meandering streams
  • Material deposited is called alluvium
31
Q

Bars

A
  • Ridge or mound of sediment (sand/gravel)
  • Middle or along banks of stream
  • When discharge or velocity decreases and the load drops
32
Q

Braided streams

A
  • Excess of sediment
  • Easily eroded banks
  • Bars split main channel into many smaller channels
  • Widens stream
33
Q

Flood Plain

A
  • Broad strip of land on either side of stream
  • Built up by sedimentation as floodwaters recede
  • Floodwaters carry suspended silt and clay (lots)
34
Q

Delta

A
  • Body of sediment deposited at the mouth of a river
  • Lowest point on the stream channel
  • Deposition occurs because river’s velocity decreases
    o River enters sea or large lake
  • Distributary: small, shifting channels
    o Carry water away from main river channel
  • Petroleum reserves possible
35
Q

Shapes of deltas

A 
- Depends on
o	Amount of sediment carried in the river
o	Waves
o	Tides
- Triangular
36
Q

Nile River delta

A
  • Wave dominated

- Note the barrier islands formed by waves

37
Q

Ganges-Brahmaputra delta

A
  • Tide dominated

- Note the sediment shaped into bars parallel to tidal current

38
Q

Deltas are a major area for sediment deposition: Example

A
  • Ex: Meking river delta
    o 90% sediment captured in delta
    o
39
Q

Delta petroleum reserves

A
  • Venezuela
  • Gulf of Mexico
  • Nigeria
40
Q

Delta’s and subsidence and example

A
  • Large volume of sediment deposition common
  • Weight of sediment -> subsidence
  • EX: gulf of mexico
    o Sediment pile > 18 000 m thick
    o Geological rate of subsidence avg 2mm/yr
    o We changed it to 8-12 mm/yr
41
Q

Alluvial Fan

A
  • Large, fan shaped pile of sediment
  • Continental setting
  • Often dry climates (but not limited)
  • Caused by loss of velocity (stream gradient changes)
42
Q

Meandering Streams

A
  • Young streams – relatively straight courses
  • As river matures, rivers develop sinuous curves: meanders
    o Caused by river velocity highest on outside of curves, so erosion promoted there
    o Point bar: sand/gravel bar deposited on inside of curves
  • Meander cutoff – especially develop during floods
    o New shorter channel across the neck of a meander
  • Oxbow lake
    o Cut-off meander
    o Crescent shaped
43
Q

Flooding, recurence interval, flood erosion, and flood deposits

A
  • Natural process on all rivers and streams
  • Usual causes: heavy rain, rapid snow melt
    o Seasonal or episodic
  • Recurrence interval: avg. time between floods of a given size
  • Flood erosion: high velocity and high volume of water
  • High water
  • Flood deposits: silt and clay
44
Q

Downcutting

A
  • Deepens valley by erosion of the stream bed
  • Smooths out
  • Base level = limit of downcutting (concave up shape of the profile)
  • Sea level is the ultimate base level
  • Resistant rocks, layers give higher base levels
45
Q

Controlling Floods

A
  • Structural dams
  • Levees (dike)
  • Channelization
    o Red river floodway
    o Building reservoirs
  • Flood plain management
    o Goal: increase water retention, lessen runoff
    o Agriculture, wetlands
    o Less urbanization
46
Q

Running Water: Grain Movement

A
  • Grain movement: controlled by settling and critical velocities dependant n grain sizes
    o Critical velocity – required for initial movement
    o Once moving, lower velocity is required for continued transport
    o Settling velocity – below which deposition occurs

Geology (20 decks)

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