π§Rivers Flashcards
What is a river drainage basin?
The area drained by a river and itβs tributaries
What is watershed?
The area of high land surrounding the river drainage basin
What are tributaries?
Small streams that feed into the main river
What is the mouth?
Where a river meets the sea or a lake
What is the source?
Where the river begins, high up in the mountains
What is a confluence?
The point where 2 or more tributaries meet together
What is the channel?
The main body of the river in which the water flows
What is erosion?
The wearing away of the land by the river
What is deposition?
The depositing (dumping) of material carried by the river
What are the 3 parts of a river?
The upper, middle and lower course
What type of erosion happens in the upper course?
Vertical erosion
What type of erosion happens in the lower course?
Lateral erosion
What are some features of a river in the upper course?
Waterfalls
Vertical erosion
Narrow V shaped valley
Rapids and large boulders
Fast flowing
Tributaries
The source of the river is found here
What shape is the upper course?
A narrow v shaped valley
What are some features of the middle course of a river?
Wide floodplains
River starts to meander
River starts to slow down
Gorges can be found here
Oxbow lakes
Raised banks caused by flooding are called leeves
What is the shape of the middle course?
Wider, less steep u shaped valley
What begins to happen in the middle course?
Meandering and slower speed
Where is the river at its slowest?
The lower course
What are some features of a river at its lower course?
River is at its slowest
Lateral erosion
Very wide flat valley
Industry and ports are found here
Large meanders
Sand and alluvium deposited
Where are industry and ports found on a river?
Lower course
What is the shape of a river at its lower course?
Very wide, flat valley
What are the 4 main processes of erosion?
- Hydraulic action
- Corrasion/Abrasion
- Attrition
- Solution/Corrosion
What is hydraulic action?
The sheer force of the water hitting the banks and river bed
What is corrasion/abrasion?
This is the process by which the bed and banks are worn down by the river load. The river throws there particles against the bed and banks, sometimes at high velocity
What is attrition?
Material (the load) carried by the river bump into each other and so are smoothed and broken down into smaller particles
What is solution/ corrosion?
This is the chemical reaction of river water. The acids in the water slowly dissolve the bed and banks, particularly limestone
What are the 4 main factors that affect the rate of river erosion?
- Gradient
- Rock resistance
- Discharge
- Velocity
What is discharge?
The amount of water in a river
How does discharge affect the rate of river erosion?
Erosion increases if the discharge increases. The more water in a river the more power it has. Therefore rivers have more power when they are full/in flood
How does the gradient affect the rate of river erosion?
A steeper gradient results in the river water being pulled by gravity, cutting down and eroding the channel. Rivers are steepest in their upper course
How does rock resistance affect the rate of river erosion?
Less resistant, softer rock erodes more quickly- for example, limestone is easily eroded- harder rocks such as igneous rocks are difficult to erode
How does velocity affect the rate of river erosion?
Erosion rate increases as velocity increases- more load can be carried and therefore more erosion occurs.
What is bedload?
The material carried by a river as it moves
How does bedload enter the river channel?
Falling in or attrition via erosion
Why does the bedload get smaller downstream?
Attrition
Where is the most material transported?
The lower course since itβs bigger so it can carry more
What can a river carry?
Rivers can on,y carry so much load depending on their energy
What is the rivers capacity?
The maximum volume of load that a river can carry at a specific point in its course
What is the rivers competence?
The biggest sized particle that a river can carry at a specific point
What are the 4 transportation processes?
- Traction
- Saltation
- Suspension
- Solution
What is traction?
The largest rocks in the river are slowly rolled along the bottom of the river by the force of the water. This primarily occurs in the upper reaches of the river
What is saltation?
Smaller rocks are bounced along the river bed. This occurs in the upper and middle sections of the river in general
What is suspension?
The water carries smaller particles of material. This process occurs throughout the course of the river, but increases the closer you get to the mouth of the river
What is solution?
Material is dissolved within the water and carries along by it. Primarily this occurs in the middle and lower reaches of the river.
What is solution?
Material is dissolved within the water and carries along by it. Primarily this occurs in the middle and lower reaches of the river.
What is deposition?
Simply dropping the material. Itβs occurs regularly along the riverbed, but also at a range of other particular points
When does deposition occur?
When the water in river channel no longer has the sufficient energy to move the material
What are 3 places that deposition occurs?
- Inner bend of meander
- Floodplain
- River mouth
Why does deposition occur on the inner bend of a meander?
The river flow is slowest here, which means it doesnβt have enough energy and deposits it
Why does deposition occur on a floodplain?
When a river floods, the water on the floodplain becomes still and has no energy so deposition occurs
Why does deposition occur at the river mouth?
The flow of the water is at its slowest, so has little to no energy and deposition occurs
Why do upper-course landforms have a steep sided v shaped valley?
The landscape is eroded by vertical erosion- the river cuts downwards into the landscape
What is an interlocking spur?
Hard resistant rock
How is a v shaped valley formed? (4 stages)
By vertical erosion
1. The river erodes downwards as boulders, stones and rock particles are bounced and scraped along the channel bed (saltation and traction)
2. As the river cuts vertically downwards, the steep sides are attacked by weathering. This breaks up and loosens the soil and rock.
3. The loosened material slowly creeps down the slope because of gravity or is washed into the river by rainwater. The river begins begins to transport it away.
4. The end result is a steep sided valley that has the shape of a letter βvβ.
When does differential erosion occur?
In waterfalls, the hard rock and soft rock are in parrallel bands which erode at different speeds.
What is differential erosion?
Eroding at different speeds.
How is a plunge pool created?
Hydraulic action and abrasion
How is a waterfall formed?
When a river flows over layers of hard rock and soft rock.
1. The soft rock starts to erode overtime, through abrasion and hydraulic action leaving an overhanging platform of hard rock.
2. The hard rocks in the plunge pool begin to wear away through attrition and the pool becomes deeper
3. The hard rock eventually becomes weak and collapses.
4. Overtime the waterfall retreats creating a vertically sided gorge