Rivers Flashcards
What is the course of a river?
The downhill flow of the river
What are the characteristics of the Upper Course?
Steep, V shaped Valley, Deep channel, Narrow Channel
What are the characteristics of the Upper Course?
Medium Gradient, Sloping Sides, Widening deepening channel
What are the characteristics of the Lower Course?
Wide channel, flat valley, deep channel
What is vertical erosion?
Deepens the valley and channel, scraping angular erosion
What is lateral erosion?
Widens the valley and channel, forms meanders
What is Hydraulic Action?
The force of the river colliding with rocks to break them
What is Abrasion?
Eroded rocks are picked up by the river and scrape against the channel
What is attrition?
Rocks crash into eachother, shattering into smaller fragments, the rocks round off
What is solution?
When rock is dissolved by river water
What is Traction?
When large boulders are forced across the river bed by water
What is saltation?
Pebbles are bounced off the river bed
What is suspension?
When small particles are suspended in water and carried by it
What is solution?
When materials are dissolved in water
What factors cause deposition?
- Water losing energy
- The volume of water falls
- There’s more eroded material and the water can’t carry it
- The water gets shallower
- The river reaches its mouth
How is a waterfall formed?
- Water flows over hard and soft rock
- Soft rock erodes by abrasion
- Creates a step
- Water flows over the step
- The waterfall undercuts the area under the step
- This causes the step to collapse
- The step falls and is swirled under the waterfall
- This erodes into a plunge pool
- Repeat! Causing Retreat
How do meanders form?
Faster currents on the outer bend, erode the outside bend
Small River Cliffs form at the bends
Since current is stronger inside, material is deposited on the outside of the bend
A slip off slope makes the inside bend shallower and the outside deeper
How are oxbow lakes formed?
Meanders continue to widen
The neck gets closer and closer until it breaks through
The river takes the shortest course and doesn’t carry sediment into the meander because there’s not enough energy
Deposition occurs and closes off the meander
What are levees?
Natural embankments along the edges
Why do we get levees?
The river floods and rises over the channel
The heaviest material is deposited at the edges of the channel
Deposited Material creates levels
What is a Floodplain?
The valley floor around the sides of a river where flooding occasionally occurs\
Material builds up here due to deposition
What are the 4 types of Soft Engineering?
- Warnings
- Zoning
- Tree Planting
- River Restoration
What do Warnings do?
Alerts through TV, Radio and Mobile Phones
Warnings: Negatives
Doesn’t prevent flooding, may give a false sense of security
Warnings: Positive
Allow for planning and preparedness, moving possessions etc.
What is flood plain zoning?
Refraining from building on parts of a flood plain
Zoning: Positives
Fewer impermeable surfaces are created
No Buildings to damage
Zoning: Negatives
Not helpful in already developed areas.
Limited expansion of urban areas
What is tree planting?
Increasing interception and lag time
Tree Planting: Benefits
Discharge and flood risk decrease
Tree Planting: Negatives
Reduces land that can be used for agriculture
What is river restoration?
Making the river more natural, allowing the floodplain to flood naturally
Restoration: Positiives
Less Maintainance required
Less risk of flooding downstream
Restoration: Negatives
Local flood risk increases
What are the 4 Hard engineering tactics?
Dams and Reservoirs
Channel Straightening
Embankments
Flood Relief Channels
What are Dams?
Artificial lakes form behind a large dam in the upper course
What is channel straightening?
Meanders are removed, making channels straighter
What are the positives and negatives of channel straightening?
P: Water leaves the area quickly
N: Faster moving water may cause erosion downstream.
What are Embankments?
Raised walls along river banks
What are Embankment Positives and Negatives?
P: The river can hold more water
N: Severe flooding may occur if the embankments break
What are flood relief channels?
Channels are built to divert water around built up areas to divert water
What are flood relief channels positives and negatives?
P: The release of water can be controlled
N: Increased discharge occurs where the channels meet the river, causing flooding
