Rivers Flashcards
Features of a drainage basin
Watershed
Source
Confluence
Tributary
Mouth
Four processes of transportation
Traction
Saltation
Suspension
Solution
What is traction and saltation
T - The action of pulling something over a surface
S - leaping or jumping
Deposition
When a river does not have enough energy to carry materials it drops them
Causes of deposition
Decreased gradient
When a river enters sea ocean or lake
Slower flow on the inside of a river bend or where the river is shallower
What’s carried up and downstream in Bradshaw model
Up - load particle size,channel bed roughness,gradient
Down - discharge,occupied channel width, channel depth,average velocity,load quantity
Upper course characteristics
Shallow
Steep valley sides
Narrow
Low velocity
Middle course characteristics
Deeper than upper course
Gently valley sides
Wider than upper course
Greater velocity than upper couse
Lower course characteristics
Deeper than middle course channel
Flat floodplains
Wider than middle course channel
Greater velocity than the middle course channel
Upland characteristics
Waterfalls
Gorges
V shaped valleys
Interlocking spurs
How is waterfalls formed
Soft rock drops undercutting the hard rock - makes plunge pool
Makes overhang of hard rock
The overhang falls into plunge pool - abrasion increases and plunge pool deeper
Process repeats waterfall retreats upstream leaving a steep sided gorge
Formation of v shaped valley
Vertical erosion is dominant in upper course
Cuts down into the river bed deepens river channel
Weathering and mass movement leads to material collapsing into river forming v shaped valley
Formation of interlocking spurs
Upper course of river starts to meander
Erosion happens on the outside of the bend
Upland areas this forms interlocking spurs
Lowland features
Meanders
Oxbow lakes
Floodplains
Levees
Oxbow lakes formation
More Distance downstream = the size of meanders increase
Erosion bends and forms meander neck
At a flood the river cuts through the meander forming a straighter course for the water
The flow of water at entry and exit from meander will be slower leading to deposition
Meander becomes cut off from the main river channel forming oxbow lake
Levees formation
• Increased friction reduces velocity and material is deposited across the floodplain gradually increasing the floodplain height
* The heaviest material is deposited first nearest to the river channel forming natural embankments called levees
Flood plain formation
The migration of meanders leads to the formation of the floodplain
High discharge may cause the river to overflow the banks
More of the water is in contact with the land surface as the water spreads across the floodplain
Opportunities from rivers
A source of food
Leisure and tourism
Generating electricity
Transporting goods and people
Used to irrigate farmland
Natural causes of river flooding
Steady rain prolonged
Landslides
Snow
Storm surge
How can flooding be increased by humans
Urbanization
Deforestation
Building of bridges and dams
Agriculture
Delta formation
Deltas are formed when streams flow into standing bodies of water
• Rivers must carry a large amount of sediment for deltas to form
• Flocculation increases deposition
• Bioconstruction increases deposition
• Delta formation must have a rapid drop in stream velocity
Case study flooding
Ganges
2.5k long
650 million people there
Opportunities - water supply,agriculture,culture,tourism,energy
Hazards - 1000 people died,700k,hectares of crops were destroyed
Solutions - fap - flood action plan which monitored flood levels and built 5k shelters
Hard engineering
Dams and reservoirs
Levees
Straightened channels
Soft engineering
Afforestation
Flood plain zoning
River restoration
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