RIVERS - PAPER 1 Flashcards
How does the profile of a river change going downstream?
At the upper course, the river is narrow and steep, because of erosion by the river along with weathering/mass movement of the slopes
At the middle course, the valley floor is wider because of lateral erosion and gentler slopes
At the lower course, there is a wide floodplain and meandering reiver, with the valley floor mostly being sediment dumped by the river
What is deposition?
Sediment dropping as it is transported by the river
Deposited in low flow conditions, can occur anywhere on the river
What are interlocking spurs?
Found in the upper course, flowing down fingers of land
Vertical erosion mainly occurs here, making the valley deeper but not eroding sidewats
How do waterfalls form?
As water flows over a junction between hard and soft rock, the soft rock erodes quicker and the water falls.
Over time, the edge of the hard rock loses support as the soft rock below is eroded
An indentation forms at the base when soft rock breaks off
Hydraulic action weakens rocks behind the waterfall, because of splashback
The unsupported hard rock breaks off
A plunge pool forms as the fallen rock breaks up and caught in the water flow, becoming trapped and drilling into the bed
A new overhand forms as undercutting continues
As erosion repeats, the waterfall retreats leaving a gorge
How do gorges form?
As the waterfall retreats, a steep sided valley is left downstream - this is a gorge
As the overhanging cap breaks off, the gorge grows longer as it retreats
How do meanders form?
Fast flowing water causes lateral erosion (abrasion and hydraulic action), forming a river cliff
There is helicoidal flow - corkscrew - where the top part of the flow erodes the outside of the bank
The flow corkscrews to the next inside bend, depositing load as friction slows flow
How do oxbow lakes form?
These form from meanders
Because of lateral erosion, the neck of the meander narrows on opposite sides of the meander bed
During high flow conditions, the neck is broken through
The river follows the new route formed, rather than the meander
Deposition fills in the gaps of the straight section, isolating the meander
An oxbow lake forms, and over time it silts up forming marshland
What are levees? How do they form?
Naturally raised river banks found on either side of a river channel prone to flooding
When the river bursts its banks, friction reduces velocity and there is deposition, the heaviest deposited closest to the river
Over many floods, the banks build up higher and higher
What are floodplains and how do they form?
During a flood, large amounts of river silt pour over the flat valley floor
The water soaks away, and the deposited sediment is left
Over many years, repeated flooding forms a thick alluvial deposit
This area is fertile; good for farming
What are the different hard engineering strategies?
Dams and reservoirs - controlling river flow by creating a reservoir
Channel straightening - cutting off meanders, creating more efficient channels
Embankments - artificially raised river banks; the river holds more water
Flood relief channels - channels made to bypass towns
What are the different soft engineering strategies?
Flood warnings - constantly monitoring rivers using technology to predict possible flooding
Floodplain zoning - restricting land use in high-risk areas
Planting trees - afforestation reduces amount of water flowing into the river
River restoration - restoring straightened channels to the original meandering patterns
What are the benefits with hard engineering strategies?
Dams - provide hydroelectric power, creates source of drinking water
Channel straightening - effective in speeding up water flow, and decreases insurance premiums
Embankments - creates walkways for locals, new riverbank habitats can be created
Flood relief channels - provides opportunities for walking and fishing. and insurance premiums are decreased
What are the issues with hard engineering strategies?
Dams - high costs (£167m in Kielder Dam), reservoir can silt over time, reducing capacity
Channel straightening - expensive and high maintenance, and the sections can look unnatural and unnatractive
Embankments - look artificial and unattractive, and can be very expensive
Flood relief channels - regular maintenance required to maintain efficiency, and habitats may be disturbed
What are the benefits with soft engineering strategies?
Flood warning - ensures safety without high cost, helps people to be prepared and act accordingly
Floodplain zoning - Reduces insurance costs, protects water meadows for wildlife
Planting trees - fairly cheap, can reduce the amount of CO2 in the atmosphere
River restoration - effective in reducing flooding downstream, restores wetland areas and increasing biodiversity
What are the issues with soft engineering strategies?
Flood warnings - equipment and expertise needed are very expensive, people won’t always respond in ideal ways
Floodplain zoning - habitats can be destroyed by building in other areas, restricts economic development in the area
Planting trees - loss of potential farmland, and can lead to higher acidity in soils
River restoration - expensive to construct and maintain, and is also an inconvenience for people using the area
