(10) + (11) The Hydrologic Cycle T3 Flashcards
(46 cards)
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%
2
Q
Fresh water usage
A
In Canada, average self-contained household used 400-1500 liters of water per person per day
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
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
5
Q
Stream
A
- Body of running water
- Confined in a channel
- Moves downhill (gravity)
- Drain the land surface
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)
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)
8
Q
Stream Valleys: Formed by…
A
- Downcutting by streams
- Mass wasting and sheetflow down banks/ valley walls
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)
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
11
Q
Dendritic drainage pattern
A
- Most common
- Uniformly erodible rock
- ‘Tree-like’ appearance to pattern
12
Q
Radial drainage pattern
A
- Looks like spokes on a wheel
- Form on high conical mountains
13
Q
Rectangular drainage pattern
A
- Develop on jointed rock (rocks that breaks and fractures in a rectangular pattern)
- Right angle bends
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
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
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
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
18
Q
What affects velocity?
A
- Gradient (slope)
- Channel shape (deep narrow (faster) vs shallow wide (slow))
- Channel roughness (creates friction and turbulence)
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
Hydraulic action
- Ability of flowing water to pick up and move rock and sediment
26
Solution
- Dissolving rock in water
- Slow but can be very effective
- Limestone: karst topography (caves)
27
Abrasion
- 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
Sediment transported as...
- 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
Water can be polluted..
with or without sediment
30
What is stream deposition and its types?
- 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
Bars
- Ridge or mound of sediment (sand/gravel)
- Middle or along banks of stream
- When discharge or velocity decreases and the load drops
32
Braided streams
- Excess of sediment
- Easily eroded banks
- Bars split main channel into many smaller channels
- Widens stream
33
Flood Plain
- Broad strip of land on either side of stream
- Built up by sedimentation as floodwaters recede
- Floodwaters carry suspended silt and clay (lots)
34
Delta
- 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
Shapes of deltas
```
- Depends on
o Amount of sediment carried in the river
o Waves
o Tides
- Triangular
```
36
Nile River delta
- Wave dominated
| - Note the barrier islands formed by waves
37
Ganges-Brahmaputra delta
- Tide dominated
| - Note the sediment shaped into bars parallel to tidal current
38
Deltas are a major area for sediment deposition: Example
- Ex: Meking river delta
o 90% sediment captured in delta
o
39
Delta petroleum reserves
- Venezuela
- Gulf of Mexico
- Nigeria
40
Delta’s and subsidence and example
- 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
Alluvial Fan
- Large, fan shaped pile of sediment
- Continental setting
- Often dry climates (but not limited)
- Caused by loss of velocity (stream gradient changes)
42
Meandering Streams
- 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
Flooding, recurence interval, flood erosion, and flood deposits
- 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
Downcutting
- 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
Controlling Floods
- 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
Running Water: Grain Movement
- 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
