Rivers Flashcards
What percentage of the earths water is freshwater (+ where is that water stored)?
2.5% of earths water -> freshwater
68.7% is glaciers and ice sheets
30% ground water
1.3% rivers, soil moisture, lakes, atmosphere
Define hydrological cycle
Continuous circulation of water in the earth-atmosphere system
Close system -> water recycled
What are examples of stores in the hydrological system?
Water in atmosphere
Surface stores -> puddle, lake, river, interception (on leaves and such)
Aquifers -> permeable rocks (can hold water)
Ice and snow
Seas and oceans
What is the hydrological cycle?
Evaporation:
Change of water from liquid -> gas due to heat (sun)
Condensation:
Water cools and changes from gas -> liquid (creates clouds)
Transpiration:
Plant releases water vapor from their leaves
Precipitation:
Transfer of water from atmosphere to surface (sleet, snow rain)
Percolation:
Transfer of water down into rocks/aquifers
Interception:
Leaves catch rain as it falls
Infiltration:
Water moves down from surface to soil
What are the different types of flow?
Throughflow:
Movement of water through soil between groundwater store and surface
Groundwater flow:
Flow of water through rock
Evapo-transpiration:
Combined transfer of water vapor from earths surface and plants
Overland flow/surface runoff:
Water flowing across surface
What are drainage basin?
Very important part of system
Drain all water which lands on earths surface
Open system
Every one has different: rock type, relief, land use, shape, size
What are features of a drainage basin?
Watershed:
an area or ridge of land that separates waters flowing to different rivers, basins, or seas
Source:
the point furthest from the mouth where the river starts, this can be an upland lake, spring or glacier
Confluence:
when two rivers converge into one river
Tributary:
small river that flows into a larger river
Mouth:
where a river enters the sea/ocean and sometimes a lake
What is drainage density?
A quantity that can describe the physical parameters of a drainage basin
Defined by the number of tributaries in the drainage basin
Lots -> high drainage density
Few -> low drainage density
What are the four erosion types in a river?
Hydraulic action:
Force of water removing material from bed and bank
Abrasion:
Materials carried by river scrape away at bed and bank
Attrition:
Material carried by river hit each other and pieces become rounder+smoother
Corrosion (solution):
when rocks are dissolved by the slightly acidic water
What is vertical and lateral erosion?
Vertical:
Dominant in upper course of rivers
Increase depth of river/valley -> erodes downward
Lateral:
Dominant in middle and lower course
Increase the width of the river/valley -> erodes sideways
What are the 4 processes for transport?
Traction:
Large rocks (or material) rolled along river bed
Saltation:
Smaller material lifted by the water -> bounces
Suspension:
Lighter material carried by river flow
Solution:
Material dissolved in the water
What is deposition?
When a river doesn’t have enough energy to carry material it drops them
What causes the reduction of energy in deposition?
Reduced discharge (lack of precipitation, abstraction (taking water))
-> friction from river bed and banks
-> friction inside bend
-> tide influence flow at estuaries and mouths
Decreased gradient (slope)
Slower flow on the inside of a bend (shallower)
River enters sea/ocean or lake
What are bedload and alluvium?
Bedload -> larger materials which are deposited first
Alluvium -> smaller materials (gravel, sand slit) which are deposited further down stream
How does the Bradshaw model show how the characteristics of a river change as a result of erosion, transportation and deposition?
As you go down stream:
Increase:
Discharge
Channel width
Channel depth
Average velocity
Load quantity
Decrease:
Load particle size
Channel bed roughness
Slope angle
What is the wetted perimeter?
the measure of how much water contact there is with the bed and the banks of a river
What are river loads?
the total amount of sediment being transported
What are the types of sediment in river loads?
Dissolved (solutes from chemical weathering of bedrock and soil) , suspended (suspended in the water) and bed load (along the bottom of the river)
Describe the form of the river valley as a long profile
Shows change in gradient
Most have a concave shape
Source upland
Upper course is much rougher and steep
Middle course -> gradient decreases
Lower course -> gradient decreases and almost flat
Describe the form of the river valley as a cross profile
Cross section from one bank to the other
Upper:
Shallow with steep sides
Narrow
Low velocity
Rough channel bed
Large bed load
High friction
Vertical erosion
Middle:
Deeper
Gentler sides
Wider
More velocity
Material decreases
Smoother bed
Lower friction
Lateral erosion
Lower:
Deeper
Flat
Wider
More velocity (minus mouth)
Smooth bed
Low friction
Deposition-> dominant
Describe the shape of the valley at different points
Upper:
Narrow V shape (spare energy used to transport boulders -> vertical erosion)
Narrow, rough, slow flow channel
Many large boulders, turbulent waters
Mostly vertical erosion
Traction and saltation
hydraulic action, attrition and abrasion
Middle:
Deeper and wider, more of a U shape
Lots of deposits
Lateral erosion
Discharge increase -> velocity increase
Suspension
Lower:
Wide valley and large channel
Smaller rocks, smother channel
Fast flowing river
Lateral erosion
How is a V shaped valley formed?
Vertical erosion -> cuts down into river bed deepens channel
Weathering and mass movement -> material from sides collapsing into river
Steep V shape
How are interlocking spurs created?
Upper course of river -> meander
Erosion on outside of bends
Upland -> interlocking spurs
How are waterfalls and gorges formed?
Formed where there is a drop in the river bed from one level to another
Drop-> change in hardness of rock (hard on soft)
Mainly hydraulic action and abrasion
Process:
Soft rock erodes quicker, undercuts harder rock and creates steep drop-off (and pool at bottom)
Creation of overhang of hard rock -> collapses
Over hang -> pool and increases abrasion and pool is deeper
Cycle (cliff retreated creates steep gorge)
