RIVERS Flashcards
What is a drainage basin?
A area of land drained by a river and its tribuities
Interception?
Leaves on vegetation, collect water
Precipitation?
- rainfall
- snow
- sleet
-(any form of moisture forming from the earths atmosphere
Surface storage?
- storage of water
- e.g, a puddle
Infiltration?
When water soaks into the soil
Evaporation?
Water is heated by the sun, and it rises as water vapour
Transpiration?
Loss of water from plants into the atmosphere
Throughflow?
Movement of water through the soil
Groundwater flow?
Movement of water through underground rocks
Surface run off?
- when water moves across the surface
- quickest form of water transfer
Evapotranspiration?
The sum of evaporation from the atmosphere and transpiration from plants
Lateral erosion?
Horizontal erosion, that makes the river banks wider
Vertical erosion?
Downward erosion, making the river banks deeper
Upper course characteristics?
- faster velocity
- steep gradient
- vshaped valley
- vertical erosion
- rough/bumpy
Middle course chacteristics?
- less steep
- wider valley
- lateral erosion
- channel gets steeper
- faster velocity
- less angular
Lower course characteristics?
- gentle gradient
- very wide valley
- deposition most active here
- high velocity
- smooth river bed
- depth is wide and deep
What is deposition and when does it take place and why?
- deposition is when everything is dropped by the river that its been carrying
- occurs most in the lower course
- if the velocity is reduced, there’s less energy as it cant be carried, so it gets dropped, as they require less energy
Traction?
Large boulders rolled along the river bed
Saltation?
Rocks bounce along the river bed, rocks get smaller and smoother
Solution?
Naturally occurring chemicals/acidic water dissolve rocks like limestone that contain calcium carbonate
Suspension
Fine like material is suspended and carried near the water surface
Attrition?
Larger rocks bang together making them smaller, larger and smoother
Hydraulic action?
Sheer force of the water blasting away small rock fragments, air expands in the cracks
Abrasion?
The load that the river is carrying wears away the bed and banks as its carried
Interlocking spurs chacteristsics?
- vshaped valley
- alternate projections sticking into the valley
- narrow channel
- convex shape
- scree slopes
Interlocking spurs formation?
-energy cant cut round valley, so it goes straight through
Waterfalls characteristics?
- plunge pool
- hard rock overlies soft rock
- undercut
- overhang
Gorges characteristics?
- steep sided
- narrow valley
- large angular bed load
- found down stream from a waterfall
- white fast flowing water
Waterfalls and gorges formation?
- form in the upper course
- hard rock e.g, granite, overlies soft rock, e.g, sandstone
- fast flowing water erodes soft rock because its easier
- leaving a undercut in the soft rock
- overhang of hard rock is left
- undercut grows larger
- overhang collapses under gravity due to a lack of support
- fallen rock falls into plunge pool, which is used to deepen it by abrasion
- waterfall moves backwards and forms steep-sided gorge
- e.g, high force waterfall
Meander chacteristics?
- steep sided river cliff, located on outside bend
- inside bend is a slip off slope
Meander formation?
- As the river erodes laterally, to the right side then the left side, it forms large bends, and then horseshoe-like loops called meanders.
- The formation of meanders is due to both deposition and erosion and meanders gradually migrate downstream.
- The force of the water erodes and undercuts the river bank on the outside of the bend where water flow has most energy due to decreased friction.
- On the inside of the bend, where the river flow is slower, material is deposited, as there is more friction.
- Over time the horseshoe become tighter, until the ends become very close together.
- As the river breaks through, eg during a flood when the river has a higher discharge and more energy, and the ends join, the loop is cut-off from the main channel.
- The cut-off loop is called an oxbow lake.
Oxbow lake characteristics?
- steep drop on the outside
- gentle slip off slope
- marsh plants colonise the edges of the oxbow lake
- fairly stagnant water in the middle of the river channel
Oxbow lake formation?
- The river is meandering across the valley.
- The river is eroding laterally (from side to side).
- The river flows faster on the outside bends and erodes them.
- The river flows slowly on the inside bends and deposits material so its course is changing.
- Continual erosion and deposition narrows the neck of the meander.
- Often during a flood the river will cut through the neck.
- The river continues on its straighter path and the meander is abandoned.
- New deposition seals off the ends and the cut-off becomes an oxbow lake that will eventually dry up.
Floodplain chacteristics?
- layers of alluvium
- meanders
- oxbow lakes
- levees
- salt marsh
Floodplain formation?
- flooding is essential for formation, coming into contact with the river banks
- generating friction
- decreasing energy
- so the large sediment is dropped further
- aluvimum
Levée chacteristics?
- steep sided banks on the channel side
- gradins of sediment gets smaller
- the smaller it is the further it moves
- fairly flat top
Levée formation?
- flooding is essential for formation
- and comes into contact with river banks, generating friction
- decreasing its energy
What is river flooding?
A natural event which occurs as a result of the river, receiving a large amount of water, beyond its normal limits
Lag time?
The time between peak discharge and peak rainfall
Rising limb?
Rapid increase in the volume of water in the river
Falling limb?
Rapid decrease in the volume of water in the river
Peak discharge?
When the river reaches its highest level
Base flow?
Normal everyday level of the river
Storm flow?
Rapid increased water level as a result of surface runoff
Bankfull discharge?
Maximum capacity of a river before it floods?
What is a hydrograph?
Records the changes in river discharge over time
Physical causes of flooding-precipitation?
- after heavy rainfall, the ground becomes saturated
- less infiltration
- more surface runoff
- shortening lag time
- increased flood risk
Physical causes of flooding-relief?
- steeper relief
- water travels faster because of surface runoff
- less opportunity for infiltration
- shorter lag time
- increased flood risk
Physical causes of flooding-temperature?
- higher temperatures means more évapotranspiration
- lower river levels
- reduced flood risk
Physical causes of flooding-geology?
- permeable pours rocks can absorb/store water
- meaning less surface runoff
- longer lag time
- decreased flood risk
Human causes of flooding-urbanisation?
- comes more imperiable surface
- infiltration cant happen
- more surface runoff
- shorter lag time
- increased flood risk
Human causes of flooding-deforestation?
- less interception
- less uptake by the roots
- more surface runoff
- shorter lag time
- increased flood risk
Impacts of flooding-social, temporary shelters?
- diseases can spread more easily
- due to cramped spaces and lack sanitation
- e.g, cholera
Impacts of flooding-social, loss of homes?
- homelessness
- lack of personal valued possessions
Impacts of flooding-social, deaths and injuries?
- increased death toll
- trauma
Impacts of flooding-social, damage to communication links?
- emergency services cant reach those in need and help them
- increased recovery time
- increased death toll
Impacts of flooding-economic, many business are forced to close?
- they cant trade
- touristes scared to visit/put off visiting
Impacts of flooding-economic, high repair/rebuilding costs?
- takes money away from other areas
- négative impact on local economy
Impacts of flooding-economic, insurance premiums may rise?
- many people cant afford to pay them
- many people left unprotected
Impacts of flooding-economic, people cant get to work?
- individual money losses
- could lead to homelessness or death
Impacts of flooding-environmental, animal and plant habitats?
-resulting in a loss of biodiversity
Impacts of flooding-environmental, fertiliser can be washed into rivers?
- can kill fish
- an kill other marine life
Impacts of flooding-enviromental, rivers can be polluted?
-polluted by sewage if flood water mixes with raw sewage
Impacts of flooding-environmental, loss of sensitive ecosystems?
- such as salt marshes and mudflats
- destroyas habitats for nesting birds
Where is boscastle?
- north coast of Cornwall
- near Plymouth
Physical causes of boscastle floods?
- stormy weather occurred leading up to the 16th of August 2004, making the ground saturated, increasing surface runoff in the area, making it flood easier
- evaporation rates were high, because the temperatures leading up to the 16th were also very high
- lots of thunder clouds/storm clouds
- located in valency valley
- located in a steep vshaped valley, less infiltration, steep relief, faster water travel by surface runoff
- higher concentration of water in the bottom of the valley
Human causes Boscastle floods?
- human built structures, low lying bridge, so the river became blocked, so the river went around the bridge, sweeping away debris like cars, and houses were affected by this
- pure lack of preparation, no flood management was in place, meaning more severe impacts and more people would of survived/not been affected
- drainage system was out of date and old, only a small capacity meaning they could overflow easier so raw sewage was everywhere
Long term consequences of boscastle flood?
- insurance premiums, so people are left unprotected, local people cant afford to pay the price
- burst sewage pipe causing long term effects as it cost a lot of money
- badly damaged buildings which costs thousands to repair
- loss of tourism and the associated income resulting in a massive economic loss
- witchcraft museum got destroyed and wasnt able to be recovered, so it had to permenatley close
- tourists didnt want to return due to fear of it happening again
Flood management scheme for boscastle?
- cost £4.6 million
- raised the car park to stop the cars from being washed away
- removed the bridge and built a higher one
- encouraged land owners to plant vegetation/trees on the valley sides to increase interception
- cleared dead trees away from the valley
- channel was widened and deepened so it could hold more water, making it less likely to flood again
Short term consequences of boscastle flood?
- roads were blocked so emergency services couldn’t reach the area, so only 2 helicopters at a time could reach them but that wasn’t enough, meaning prolonged rescue
- houses were destroyed by cars and trees being carried at a high speed by the fast flowing river
- people were trapped and had to climb to the roof of their houses for recovery
- burst sewage so water was contaminated
- homelessness, because temporary accommodation/shelter had to be set up, as the guest houses were fully booked up due to the fact it was in the summertime
Damns and resivoir?
They store the water, then release it in a controlled manor
Dams and resivoirs advantages?
- provide hydroelectric power, which is sustainable
- provides drinking water for wildlife to drink
Disadvantages of dams and resivoirs?
- the floods displace people, usually farmers from their homes
- unattractive, interferes with migration of fish
Channel straightening?
The rivers travel faster, meaning the water travels faster, which reduces flood risk
Channel straightening advantages?
- easier for navigation for boats, helping trade and the economy
- insurance costs go down, if its less likely to flood
Channel straightening disadvantages?
- visually unattractive
- habitats can be disrupted
Embankments?
Raising and strengthening the river banks, meaning the river can hold more water, so flooding is less likely
Émbankments advantages?
- cheaper
- provides habitats for animals
Embankments disadvantages?
- higher maintience costs
- visually unattractive
Flood relief channels?
Atrifically made channel, which is a backup channel for a river that floods a lot
Flood relief channel advantages?
Insurance costs are lower in the area because the flood risk is less likely
Flood relief channels disadvantages?
Expensive to set up, maintain and repair
