2.2 Rivers Flashcards
Opportunities of living near a river
- abundant water supply
- fertile soil
- water for transport (e.g. trading, fishing, tourism)
- leisure and tourism (more job opportunities)
- navigation
- lower house prices
5 management for river flooding
- dams
- widen, deepen, straighten river to carry more water
- plant more trees to block water from overflowing
- naturally letting it flood to prevent flooding in other areas
- planning policies (warnings and evacuation procedures)
2 hazards of rivers
- Spread of diseases (e.g. Malaria)
- Flooding –> deaths, loss of homes, infrastructure destroyed, shortage of food and water, fires
Definition of ‘drainage basin’
Area drained by the river
Definition of HEP
Hydroelectric power
4 causes of flooding
- Steep channel –> causes fast surface run-off
- Drainage basin with impermeable rock –> rock does not absorb any water
- Drainage basin in an urban area –> impermeable concrete/flooring
- Deforestation, over-cultivation, population pressure –> causes soil erosion –> increase in amount of sediment
Hydraulic action
The force of flowing water alone breaking off material from the bed and banks of a river
Abrasion (corrasion)
Pebbles and rocks rub against the bed and banks of the river (like sandpaper), causing them to crack and break off
Attrition
Material that wear each other away as they smash into each other
Corrosion (solution)
Acids in the river dissolving material (limestone)
Vertical erosion
the wearing away and deepening of the river bed
Lateral erosion
the wearing away and widening of the sides of the river
Describe the profile of the upper course of the river
- Steep slopes
- Thin river channel
- Steep v-shaped valley
- Deep in places
Describe the profile of the middle course of the river
- shallow slopes towards the mouth
- wider river channel
- v-shaped valley
- river begins to meander
- deeper channel
Describe the profile of the lower course of the river
- almost at sea level
- gently sloping to its mouth
- wide, shallow valley
- large floodplain
- meanders
- wide channel
- deep and smooth sides
Describe the landform of the upper course
- More roughness, turbulence and friction
- Steep slopes = vertical erosion
- Shallow river bed
Describe the landform of the middle course
- meanders
- oxbow lakes
How are meanders formed?
Helical flow of water causes lateral erosion, forming bends
Fastest current is forced to the outer bank
Deposition in the inner bank as current slows + more friction
Hazards of living near rivers
Spread of diseases - Malaria Flooding - Deaths - Loss of homes - Infrastructure destroyed - Shortage of food + water Fires
Opportunities of living near a river
- Abundant water supply
- Water for transport (trading, tourism and fishing)
- Leisure and tourism –> more job opportunities
- Fertile soil
- Lower house prices
- Navigation
- Electricity for power stations
Factors that influence the shape of the river
The rate of vertical erosion The rate of lateral erosion by weathering and erosion The geology of the valley The climate of the valley Time
How are waterfalls formed?
- River flows over hard rock onto soft rock
- Soft rock at the bottom erodes more quickly
- The soft rock erodes until a plunge pool is created
- Hard rock will form an overhang, forming a waterfall
- Over time, the overhang becomes bigger, until the hard rock is no longer supported by the soft rock underneath
- The overhang falls, forming a gorge
How are oxbow lakes formed?
- Erosion continues in meandering river → causing it to become more narrow
- The curves eventually curve and join together → forms a circular river
- Substances deposited on the inner banks
- As deposition continues, new land is formed
- The meandering section falls apart from the river → creates an oxbow lake
How are deltas formed?
- Occurs where a river carrying large amounts of sediment meets a lake or the sea → causes rivers to lose energy + deposit material
- Usually occurs where the rate of deposition by the river and tides is far more than the sea currents can remove
- Rate of flow slows down towards the mouth
- Deposition of material on the river bed occur
- When ocean calms, more sediment piles up → forms new land
- Deltas form where river mouths are blocked with sediment, causing the main river channel to split into hundreds of smaller channels
Causes of flooding
Steep channel: causes fast surface run-off
Drainage basin with impermeable rock: x percolation through rock layer → surface run-off
Drainage basin in an urban area: impermeable concrete/flooring
Deforestation, over-cultivation, population pressure: causes soil erosion
Increase in amount of sediment, decrease in cross sectional area
How are levees formed?
Formed when river floods
Heavy materials are deposited first when flooding → they require more energy
Deposited at channel edges
As more floods occur, the material builds up, creating a side barrier —> levees
How are flood plains formed?
Area of deposited material found beside the river → where river flood exceeds the discharge
When rivers flood, they deposit material in the water
Water also erodes the bottom of the land
As they deposit material to the sides → creating a barrier + river erodes the land
Flood plain is formed
Lateral erosion allows the river to meander
Creates a wide valley floor → floodplain
Management of flooding (hard engineering)
- Dams across the river to control the amount of discharge → water held back in reservoirs
- River engineering: widen/deepen/straighten river to carry more water, change river direction → does not run-off to land
Management of flooding (soft engineering)
- Afforestation → planting trees nearby to increasing interception → block water
- Managed flooding: allow river to flood naturally to prevent flooding in other areas
- Planning: policies to protect areas near rivers, installing a system of sirens and warnings and evacuation procedures, a store of sand for emergency use, temporary, moveable metal barriers that can be put up quickly
