River Enviounmnets Flashcards
What is erosion
River erosion is the wearing away of the landscape by the action of water.
What is vertical erosion?
When a river has a large load made up of coarse materials these scrape or rub against the channel bed, eventually lowering the level of the bed, to create steep valley sides. This is known as vertical erosion.
What is lateral erosion?
When a river is flowing fast the water has enough energy to wash away parts of the bank of the river. This leads to undercutting and collapse.
What is corrosion
Scraping and rubbing action of the load carried by the river. Rock fragments scrape along the bed and banks wearing them away.
What is attrition?
When particles become smaller and rounder in the river as they collide with one another, the bed and the banks.
What is solution
When a river flows over the alkaline underlying geology minerals in the rock are dissolved by the weak acids in the water. As they are dissolved they are carried in solution.
What is hydraulic action?
Caused by the sheer power of moving water. Air is pushed into the cracks and the rock is broken apart.
What is transportation?
The movement of material across earths surface
What is traction
The rolling and sliding of large rocks along the river bed. This process requires a lot of energy, and the largest bed load is only moved in times of flood.
What is saltation?
The bouncing of medium sized / pebbles load along the river bed.
Suspension
Very small load, which is continually held up or suspended in the water. Makes the water opaque
Solution (transportation)
Soluble minerals are carried via solution transport.
What is deposition
Deposition is the dropping of material on Earths surface.
Why does deposition occur?
Energy of water reduces. This could happen because
The river channel reaches a smaller gradient
River enters lake or sea
Discharge is reduced following a period of low rainfall
Areas of shallow water where friction reduces velocity.
What is discharge
The amount of water in a river which is passing a certain point in a certain time. Measured in cumecs (cubic meters per second)
How is a waterfall formed?
Hard rock and soft rock
Soft rock erodes faster creates a step
Hydraulic action and abrasion deepen it until a waterfall is formed
Plunge pool created by erosion
Blocks of rock are broken down in plunge pool and erode the base of waterfall causing it to collapse
This collapse causes a gorge to from back up the river stream .
What is a meander
Bends that develop in a river channel as the gradient evens out.
Characteristics of the outside of the bank of meander
Faster
Undercut bank
Fine material in suspension
Characteristics of inside of meander
Slower
Slip-off-slope
Sand and shingle deposited on inside of the bed
What is a floodplain
An area of flat low lying ground over which a river meanders, formed of mainly river sediment and subject to flooding
What is a levee
A ridge of sediment deposited naturally alongside a river in times of flood
Physical causes of flooding
Heavy rainfall
Prolonged rainfall as in monsoon climate
Melting of a glacier or snow
Underlying rock is impermeable or clay soil
Ground is frozen.
Human causes of flooding
Deforestation
Urbanisation
Narrowing a river channel
Building of levees.
What is the example of a flood in the British isles
Somerset on the rivers tonnes and parrett.
Physical causes of flooding in Somerset
Impermeable bed rock
Heavy rainfall (207mm in jan)
High tides
Human causes of Somerset flood
River tonnes and river parrett hadn’t been dredged properly in 20 years.
Extra water sent into the levels from Taunton and Bridgewater
Types of hard engineering used on Mississippi flood
100 dams on the Ohio river
Levees were strengthend and raised to 15m along 3000 km of the river.
Straightened the river channel
Types of soft engineering used in Mississippi flood
Afforestation
Safe flood zones
Washlands- Morganza spillway was opened to flood 12,000km2 of farmland in Louisiana deliberately.
