Rivers

• 3 courses of a river

  1. Upper
  2. Middle
  3. Lower
• 2 types of erosion in a river

  1. Vertical
  2. Lateral
• Water falls and gorges

  1. Hard rock lies on-top of soft rock. Soft rock is eroded first
  2. Over time the soft rock erodes leaving the hard rock to undercut which forms an overhang
  3. The hard rock will then give into gravity and fall
  4. Collapsed rock forms a plunge pool
  5. This process continues and the waterfall retreats upstream
  6. A steep-sided valley is left where the waterfall once was. This forms a gorge
• Interlocking Spurs

  • Form in the upper course
  • River erodes vertically
  •  If there are areas of hard rock which are harder to erode, the river will bend around it
• Meander

  1. Current is faster on the outside bend so it is deeper there
  2. The outside bend has more energy so it erodes more forming a river cliff
  3. The current is slower on the inside bend so it is shallower there
  4. So material is deposited forming a point bar over time
• Oxbow lake

  1. Erosion causes outside bend to get closer until there is a small bit of land (called the neck)
  2. The river breaks through this land during a flood and water will flow the shortest course
  3. Deposition cuts off the meander leaving an ox bow lake
• Flood plains

  1. A wide valley floor that occasionally gets flooded
  2. When a river floods onto a flood plain the water deposited material making the flood plain higher
  3. Meanders migrate across the flood plain making it wider or flatting it if migrating down stream
  4. Deposition from point bars also builds up the flood plain
• Levees

  1. during a flood eroded material is deposited over the flood plain
  2. The heaviest material is deposited closest to the river
  3. Over time the deposited material builds up creating a levees along side the channel
• How rainfall affects river processes and landscapes

  • wetter climates have higher discharge which increases rate of erosion
  • Transportation increases in higher discharged rivers
  • Chemical weathering is more common in a rainy climate
• How temperature affects river processes and landscapes

  • Low temps means more freeze thaw weathering
  • High temps means more chemical weathering
  • Both of these can lead to more mass movement
• How storms affect river processes

  1. Heavy rainfall make the ground saturated making mass movement more likely
  2. Rapid increase in water volume
  3. Increase in transportation
  4. Flooding cause by storms can lead to ox bow lakes and levees
• How drought affect river processes

  1. Water volume drops
  2. less erosion
  3. less mass movement
• How urbanisation affects river processes

  1. Urban areas have impermeable surfaces so there is more surface run-off
  2. Urban areas can suffer from heavy flooding if built on a flood plain
  3. River defenses are put in place which can change the landscape
• How agriculture affects river processes

  • Taking water from rivers to water crops
  • Exposed soil is washed away making a large sediment load so more deposition downstream
  • drainage systems quickly increase discharge and erosion when there is heavy rainfall
• How industry affects river processes

  • Impermeable surfaces
  • Air pollution allows for more chemical weathering
  • Deeper channels are made for boats which reduces flooding
  • Boats can disrupt the water which can increase erosion
• Physical factors that cause flooding

  • Prolonged rainfall
  • Geology
  • Relief
  • Heavy rainfall
• Human causes of flooding

  • Buildings are made from impermeable material which increases surface run off
  • Deforestation means there are less trees to intercept the precipitation so there is more infiltration
• Affects of flooding on people

  1. Kill or injure
  2. Lead to a lack of clean water
  3. Possession are damage or lost
  4. People loss their properties
  5. No electrical power for several days
  6. Important services are closed
  7. Businesses may have to shut down
  8. Transport can be affected
• Affects of flooding on the environment

  1. Contaminated water which can pollute wildlife habitats
  2. Farmland ruined by silt and deposited materiel after flood
  3. River banks erode cause changes to the river landscape
  4. Trees can be uprooted
• Dams and reservoirs

  • Dam is a huge built across a river. A reservoir is an artificial lake that forms behind the dam
  • Reservoirs store water which reduces flood risk and can be used for drinking water or used to generate power
  • Dams are expensive to build and settlements must be cleared if you are in the site of the reservoir.
  • Changes to depositional formations downstream due to material being deposited in the reservoir
• Channelisation- the widening, straightening or deepening of a river to speed up the water so high volumes of water can pass through an area quickly

  • More water can be held in the channel
  • It can be used to reduce flood risk in built-up areas.
  • Speeding up the river increases flood risk downstream.
  • needs to be re deepened frequently (Dredging)
• Embankments - Raising the banks of a river means that it can hold more water

  • Cheap with a one-off cost
  • Allow for flood water to be contained within the river
  • Look unnatural
  • Water speeds up and can increase flood risk downstream
• Flood Plain Zoning -restrictions put on building on parts of a floodplain

  • Cheap and reduces flood risk and flooding impact
  • Limits the expansion of urban areas
• Washlands - areas of a floodplain that are deliberately allowed to flood

  • Store high amounts of discharge
  • Provides a wetland habitat
  • Area of land cannot be used for anything else
• Flood relief channel - The floodwater flows into the relief channel which takes it away

  • Removes excess water from the river channel to reduce flooding
  • Expensive to build
  • If water levels continue to rise, the relief channel may also flood