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 gradient
- 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
Name the 2 types of erosion?
lateral
vertical
What is vertical erosion?
- deepens river valley and channel 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 and channel 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?
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?
waterfalls form where 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?
- doesn’t 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, England
Why did Banbury need a management scheme?
- 1998- flooding led to closure of the twon’s railway station, local roads were shut, caused £12.5 million of damage
- more than 150 homes and businesses were affected
- 2007- town was hit by floods again
What has been done to reduce the risk of flooding in banbury
- 2.9km earth embankment built parallel to M40 to create a flood storage area
- raising A4361 road in the flood storage area
- improvement to drainage beneath roads- prevents flooding
- new pumping station to transfer excess rainwater to river below town
What are the social benefits with the flood management scheme in Banbury
- raised A361 route into Banbury will be open during a flood to avoid disrupting peoples lives
- quality of life for local people= improved- new footpaths and green areas
- reduced levels of anxiety and depression through fear
What are the economic benefits with flood management scheme in banbury
- cost of scheme £18.5 million
- by protecting 441 houses and 73 commercial properties- benefits are estimated to be over £100 million
What are some environmental issues with the Banbury flood managment scheme
- around 100,000 tonnes of earth were required to build embankment- this was extracted from nearby creating a small reservoir
- part of floodplain will deliberately be allowed to flood if river levels are high
where is banbury
-located in the cotswolds hills on the floodplain of the River Cherwell
