Rivers Flashcards
What is the rivers course?
the path of a river as it flows downhill
What are the three courses of a river?
upper, middle, lower
what do rivers form as they flow downhill?
channels and valleys
What does the long profile of a river tell you?
how the gradient changes over different courses
What does the cross profile of a river show you?
what a cross section of the river would look like
Describe the upper course of a river?
- steep
- v-shaped valley
- steep sides
- narrow, shallow channel
Describe the middle course of a river?
- medium gradiant
- gently sloping valley sides
- wider deeper channel
Describe the lower course of a river?
- gentle gradient
- very wide
- very flat valley
- very wide, deep channel
what can erosion be? two things
lateral or vertical
What is vertical erosion?
- deepens river valley making it v-shaped
- dominant in upper course of river
- high turbulence causes rough rocks to be scraped along river bed causing intense downward erosion
What is lateral erosion?
- widens river valley during formation of meanders
- dominant in middle and lower courses
What are the 4 processes of a river?
hydraulic action, abrasion, attrition, solution
What is hydraulic action?
the force the water breaks rock particles away from the river channel
What is abrasion?
eroded rocks picked up by the river scrape and rub against the channel causing it to wear away
What is attrition?
eroded rocks picked up by the river smash into each other and break into smaller fragments . their edges become rounded as they rub together
What is solution?
river water dissolves some type of rock
What are the 4 processes of transportation?
traction, saltation, suspension and solution
What is traction?
large particles like boulders are pushed along the river bed by the force of water
What is suspension?
small particles like silt and call are carried along the water
What is saltation?
pebble sized materials are bounced along the river bed by the force of water
What is solution?
soluble materials dissolve in the water and are carried along
What is deposition?
when a river drops the eroded material its transporting
where are waterfalls and gorges found?
in the upper course of the river
Explain how a waterfall is formed?
- river flows over area of hard rock and then soft rock
- the soft rock is eroded more then hard rock creating a step in the river
- as water goes over step it erodes more and more of softer rock
- steep drop eventually created and waterfall formed
- hard rock eventually undercut by erosion, becomes unstable and collapses
- collapsed rocks are swirled around at foot of waterfall where they erode soft rock by abrasion making a plunge pool
- over time more undercutting and collapsing occurs
- waterfall retreats leaving a steep gorge
Where do waterfalls form?
were river flows over an area of hard rock followed by soft rock
Explain how interlocking spurs occur?
- in upper course, mostly vertical erosion creating steep v-shaped valley
- rivers arnt powerful enough to erode laterally, they have to wind around the high hillsides that stick out wither side
- the hillsides that interlock with each other as river winds around them are called interlocking spurs
What are some soft engineering methods to reduce the effect of flooding?
flood warning, preparation, flood plain zoning, planting trees, river restoration
what are flood warnings?
environmental agency warns people about possible flooding through TV, radio, internet and newspapers
What is preparation for floods?
buildings modified to reduce the amount of damage a flood could cause.
people make plans if a flood occurred
keep items needed in accessible place
What is flood plain zoning?
restrictions prevent buildings on parts of a flood plain that are likely to be effected by flood
What does planting trees do for floods?
planting in river valley increases interception of rainwater and also increases lag time
What does river restoration do for floods?
making rivers more natural, removing man made levees so flood plains can flood naturally
What are the benefits of flood warnings?
- impact of flooding is reduced
- give people time to move possessions upstairs, put sandbags in position
What are the disadvantages of flood warnings?
- don’t stop flood from happening
- people may not hear or have access to warnings
What are the benefits of preparation?
- impact of flooding is reduced
- buildings less damaged
- people know what to do
- less likely to worry about threat
What are the disadvantage of preparation?
- doesnt guarantee safety from a flood
- false sense of security
- expensive to modify buildings and homes
what are some advantages of flood plain zoning?
- risk of flooding is reduced
- impermeable sufaces arnt created
- impact of flooding is reduced - no buildings to damage
What are some disadvantages of flood plain zoning?
- expansion of urban area is limited
- no help to areas that have already been built on
What are some advantages of planting trees?
- dishrag and flood risk are reduced
- vegetation reduces soil erosion in valley and provides habitats to wildlife
What are some disadvantages of planting trees?
-less land for farming
What are some advantages of river restoration?
- less risk of flooding downstream because discharge is reduces
- little maintenance
- more habits for wildlife
What are some disadvantages of river restoration?
- local flood risk can increase
Name a place that needed flood management?
banbury
Describe banbury?
in cotswold hils about 50km north of Oxford.
population of around 45000 people.
most of town on a floodplain of river cherwell and river thames
How has Banbury been effected by flooding?
- 1998 flooding led to closure of towns railway station, shut local roads and caused 12.5 mill of damage
- more then 150 homes and buisnesses were effected
- in 2007 town was hit again by flooding
What has been done in banbury to reduce risk of flooding?
- 2.9km earth embankment was built parallel to M40 motorway to create flood storage, 4.5 meters tall and is capable of 3 million cubic meters of water
- flow control structures to control rate of flow downstream, excess water backs up behind structure filling resourvoire
- raising A361 road in the flood storage area and added drainage
- earth embankments and flood-walls to protect property and businesses ( Pro-drive)
- new pumping station to transfer excess rainwater into the river below the town
- Biodiversity action plan, habitat with ponds, trees and hedgerows to absorb and store excess water
social benifits of flood management scheme?
- raised A361 will be open during flood
- quality of life for locals improved with new footpaths and green areas
- reduced levels of anxiety through fear of flooding
What are some economic benefits of flood management scheme?
- cost was £18.5 million
- by protecting 441 houses and 73 properties benefits are over £100 millon
enviromental benefits + downsides of banbury flood scheme?
- 100000 tonnes of earth were required to build embankment
- biodiversity action plan created
- part of floodplain deliberaterly allowed to flood
