Flashcards
River flashcards
Cards in this deck (54)
- 1How does braiding form?1. Occurs when a river carrying a vast amount of eroded sediment
2. If the river's velocity drops of the sediment becomes too much for the river to carry, sediment is deposited in the channel
3. This causes the river to divide into small, winding channels that rejoin - 2How do floodplains form?1. When a river overflows its banks and floods the flat land either side of the river, there's an increase in the wetted perimeter and reduction in hydraulic radius
2. This increases friction, reducing the velocity of the river and causing fine silt and sand to be deposited - 3How do levees form?1. Natural raised embankments formed as a river overflows its banks
2. During a flood, material is deposited across the floodplain as the river loses velocity and energy due to increased friction
3. Heaviest material is dropped first closest to river channel
4.Over time material builds up - 4How do deltas form?1. When a river reaches the sea, the energy of the river is absorbed by the slower moving water of the sea
2. This causes the the river to deposit load
3. Deposits build up on the sea bed until the alluvium rises above sea level, partially blocking mouth of the river
4. River has to braid to reach the sea which forms a delta - 5What is rejuvenation?Base level lowered.
1. Ground level rising (crustal uplift)
2. Drop in sea level
River terraces and incised meanders - 6How do waterfalls form?1. Hard rock meets soft rock and the soft rock gets eroded faster, causing a step
2. Water flowing over the step speeds up due to lack of friction and increases erosive power causing erosion and undercutting
3. Hard rock is undercut and collapses
4. Deep plunge pool carved out by abrasion, as bits of rock is swirled round by turbulence
5. Retreat leaving steep-sided gorge - 7What are rapids?Relatively steep sections of river with turbulent flow where there are several sections of hard rock
Mini waterfalls - 8How are potholes formed?Small circular hollows in the river bed
1. Formed by abrasion as turbulence swirls rivers bed load in a round circular motion
2. Causes it to rub and scrape out holes - 9How do meanders form?1. Alternating pools and riffles develop at equally spaced intervals along a river
2. Channel deeper in pools more efficient, greater energy & erosive power
3. Energy lost due to friction over riffles
4. Flow uneven and maximum flow on one side of the river
5. Turbulence increases in and around pools as water speeds up
6. Water begins to twist and coil
7. Helicoidal flow, spiral bank to bank, causes further erosion and deepening of pools. Eroded material deposited on inside of next bend when loses energy - 10What is deposition?Dropping of eroded material
Happens when the river loses energy
When it slows down, it has less energy and drops some of its load - 11What are the four types of transportation?1. Traction- pushed
2. Saltation- bounced
3. Suspension- carried
4. Solution- dissolved - 12What are the four types of erosion?1. Hydraulic action- waves and pressure
2. Attrition- hitting each other
3. Abrasion- rock hitting river bed
4. Solution- dissolving of rocks - 13What is the upper stage of a river like?Lots of erosion (abrasion)
Boulder, traction
Little deposition
Steep gradient
V shape valley, vertical erosion
Steep sloping sides - 14What is the middle course of a river like?Lateral, abrasion, attrition erosion
Suspension
Sand and gravel deposited
Gradient decreases
Wider valleys
Material deposited = floodplain - 15What is the lower course of the river like?High velocity and discharge
Little erosion
Suspension and solution
Sand, silt, clay deposited
Little potential energy low gradient
Wide valley and flodoplain
Gently sloping sides - 16What is river velocity influenced by?Gradient
Discharge
Shape and roughness - 17What does a long profile show?How the gradient of the river channel changes from the river's source to its mouth by showing the height of the river bed above the base level for the whole length of the river
- 18What does cross profile show?Shows you what a cross section of the river channel or river valley looks like
- 19What does headward erosion do?Makes the river longer
- 20What does vertical erosion do?Makes the river deeper, happens in upper stage of a river
- 21What does lateral erosion do?Makes the river wider, occurs in the middle and lower parts of a river
- 22What does the hjulstrom curve show?Link between river velocity and competence
- 23What is capacity?Total amount a river can carry
- 24What are the physical factors that affect flooding?1. Sparse vegetation/ deciduous trees
2. Circular drainage basin
3. Steep slopes
4. High drainage density
5.Impermeable ground - 25What are the human factors that affect flooding?1. Urbanisation
2. Deforestation
3. Flood management strategies
4. Agriculture
5. Climate change - 26What are examples of hard engineering to protect a river from flooding?1. Dams
2. Levees
3. Channel straightening
4. Diversion spillways - 27What are examples of soft engineering to protect a river from flooding?1. Forecasts and warning
2. Wetland and river bank conservation
3. Land use management
4. Alteration of urban surfaces
5. River restoration - 28How do dams work?Huge walls built across rivers
A reservoir is formed behind the dam.
Water is released as a steady flow throughout the year
Flood water is caught by the dam which prevents flooding downstream. - 29What are advantages of dams?1. Turbines often built into dams which generate electricity
2. Steady water release allows irrigation of the land below throughout the year
3. People can use reservoir for recreational activities such as sailing - 30What are disadvantages to dams?1. Expensive
2. Land is flooded when reservoir is created can destroy farmland
3. Affect wildlife e.g salmon migrating
4. Trap sediment normally carried in rivers, can cause dam to fail and lead to increased erosion downstream - 31How does channel straightening work?Where meanders are removed by building artificial cut-throughs, makes water flow faster and reduced flooding as water drains downstream quicker. Doesn't build up to a point where river channel can't contain it anymore
- 32What are advantages to channel straightening?1. Takes less time to navigate the river because it has been made shorter
- 33What are disadvantages to channel straightening?1. Disturbs wildlife
2. More erosion occurs downstream because the river flows faster
2. Flooding may happen downstream, as flood water is carried there faster - 34How do levees work in protecting the river from flooding?Embankments built along rivers
The river can hold more water without overflowing and so it flows less often - 35What are advantages to levees?1. Allow the floodplain to be built upon
- 36What are disadvantages to levees?1. Quite expensive
2. Risk of severe flooding if the levees are breached - 37How do diversion spillways work?Channels that take water elsewhere if the water level in the river is too high
Water is normally diverted around an important river or to another river. Prevent flooding because discharge is reduced. Often have gates so there is control - 38What are disadvantages to diversion spillways?1. An increase in discharge when the diverted water joins another river, could cause flooding below that point
2. If spillways are overwhelmed, water will flood areas not used to flooding, this could cause bigger problems - 39What is land use management?Planning restrictions prevent buildings or roads being constructed on the floodplain
More water can infiltrate so there's less surface run off, which reduces discharge - 40What are advantages to land use management?1. There are no new buildings or roads on the floodplain to be damaged, so impact of flooding reduced
2. Provides recreational activities such as football fields - 41What are disadvantages to land use management?1. Restricts development, especially when there is a shortage of housing
2. Can't be used in areas that are already urbanised - 42What is wetland and river bank conservation?Wetlands store flood water and slow it down, this reduces flooding downstream so conserving gives natural protection.
Planting trees increases interception and lag time and reduces discharge - 43What are advantages to wetland and river bank conservation?1. Vegetation protects the surface soil from erosion
2. The vegetation provides habitats for wildlife - 44What are disadvantages to wetland and river bank conservation?1. Less land available for farming
- 45What is river restoration?Involves making the river more natural such as removing man made levees. Floodplain can flood naturally. As water spreads out on the floodplain discharge is reduced
- 46What are advantages to river restoration?1. Little maintenance is needed
2.River provides better habitat for wildlife - 47What are disadvantages to river restoration?1. Local flood risk can increase, especially if nothing is done to prevent major flooding
- 48What is alteration of urban surfaces?Building porous pavements or soakways increases infiltration which reduces rapid surface runoff to the river channel
- 49What are advantages to alteration of urban surfaces?1. Any pollutants in the water are filtered out by the soil before the water reaches the channel
- 50What are disadvantages to alteration of urban surfaces?1. Expensive
- 51Where has hard engineering been used to protect from flooding?Yangzte river, China
- 52Where has soft engineering been used to protect from flooding?Abingdon, South east england
- 53What MEDC suffered from flooding?Carlisle, Cumbria 2005
- 54What LEDC suffered from flooding?South Asia, 2007
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- Geography AS (Rivers) Flashcards on River flashcards, created by becca_walls on 08/05/2015.
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