Water on the Land Flashcards
What are the 4 types of erosion and their brief definitions?
Hydraulic action: the force of the river against the banks and bed wears away at the rock
Abrasion: Rocks carried alongg by the river wear down the river bed and bank
Attrition: Rocks carried by the river smash into eachother and become smoother rounder particles
Corrosion/solution: soluble particles dissolve into river
What are the 2 directions of erosion?
Vertical- downward action that deepens the river (dominant in upper course)
Lateral erosion- sideways that widens river channel (dominant in lower course)
What’s are the 4 different processes of transportation?
- Solution- minerals are dissolved in the water and carried in solution
- Suspension- fine light material carried in the water
- Saltation- small pebbles and stones are bouncd along the river bed
- Traction- large boulders sand rocks are rolled along the river bed
What are the features of the upper course?
Vertical erosion, narrow and shallow river channels, large bedload, steep v- shaped valley, transportation: traction and saltation
What are the features of the middle course?
Lateral&vertical erosion, wider and deeper river channels, small bedload, meanders&oxbow lakes, transportation: suspension and solution, deposition and erosion
What are the features of the lower course?
Lateral erosion, wide and deep channels, suspended sediment, floodplains and leeves, deltas and estuaries, transportation; suspension and solution, mostly deposition
How are waterfalls formed?
- Softer rock eroded, causing an undercut in the hard rock
- Hard rock overhangs, collapses, adding large rocks to the base of the waterfall
- The power of the water falling into thhe base erodes the base into a plunge pool
- The undercutting and collapse is repeated
How are gorges formed?
- The constant undercutting and retreat of a waterfall process causes the waterfall to retreat upstream
- The retreat creates a steep sided gorge
How are meanders formed?
- As the river flows downstream, gradient over which it flows becomes less steep
- Lateral erosion increases
- To use extra energy the river begins to meander
- The erosion on the outside of meanders widens the valley, removing the interlocking spurs
- On the outside bend the water is deeper, has a faster current which causes a river cliff
- On the inside bend there is slack water, a less strong current and some deposition which causes slip-off slope
How are oxbow lakes formed?
- Meander bends become larger and more vigorous
- Continued erosion on the outside of the bends causes the neck to narrow and break
- Oxbow lake is then formed away from river
How are leeves formed?
- When a river floods, it spills onto a floodplain taking any sediment with it
- The finest sediment is deposited further along the floodplain
- The heavier sediment is deposited first and builds up into banks called leeves
What are the features of a river basin?
- River Source
- Tributary: small river channel
- Main river channel
- Confluence: where two rivers meet
- Mouth of the river
- Watershed: Boundary where any rain that falls wiithin it will go into the river
What is the definition of river discharge?
The volume of water in a river flowing- measured in cumecs (cubic metres per second)
What are the steps of the hydrological cycle?
Clouds- Precipitation - Percolation (or Transpiration to Air) - Ground water - Run off - Ocean - Evaporation - Air
What are the physical factors affecting river discharge?
- Rainfall- more rain= higher river levels
- Temperature- higher temperature= more evaporation
- Relief of the land- steep land= increased surface run off
- Rock type- impermeable rock= increased surface run off
What does a hydrograph do?
It shows how a river responds to a period of rainfall.
On hydrographs what are precipitation and discharge shown as?
Precipitation: bars
Discharge: lines
What are the definitions of: peak rainfall, peak discharge, lag time, rising limb and falling limb?
Peak rainfall: when rainfall is at its highest (mm)
Peak discharge: when river flow has reached its max (cumecs)
Lag time: the time between peak rainfall and peak discharge
Rising limb: when the river flow is rising
Falling limb: when the flow begins to fall after it’s peaked
What are the human factors affecting river discharge?
- Urbanisation- towns and cities= more impermeable surfaces (tarmac/concrete)
- Deforestation- fewer trees= less precipitation interception and increased surface run-off
What was the date, river and location of the Boscastle floods?
16th of August 2004, River Valency, Cornwall
What were the causes of the Boscastle floods?
Local area saturated by weeks of rainfall, 8 inches of rainfall fell on Boscastle, located in a steep v- shaped valley, confluence of three rivers increased discharge, car parks along the Valency increased the run off
What are the names of the 3 rivers that meet in Boscastle? (strippers)
Valency, Jordan and Paradise
What were the effects of the Boscastle floods? (Economic, environmental, social,)
Economic: infrastructure destroyed (homes/offices/bridges etc), visitor centre collapsed, tourism reduced, homes devalued, £15m in damages and claims
Social: Infrastructure destroyed, transport destroyed, no deaths
Environmental: Silt and debris left in village after waters subsided
What were the immediate and long term responses to the Boscastle floods?
Immediate: EA issues flood warnings, rapid evacuation, fire brigades and police on the scene within an hour, RAF helicopters saved 150 people, lifeboats go to houses, tmeporary accomodation set up on football pitch
Long term: People banned from homes for 10 days, silt and debris cleared, telephone/water/electricity all restored within 6 months, coompensation provided to home owners
