Rivers part 4

• What is flooding


  Flooding is when land which isn't usually underwater becomes inundated (covered). This happens when a river cant hold the amount of water in it
• When does flooding usually occur

  after heavy rainfall, often in winter

  sudden floods can occur during torrential storms (flash floods)
• What are the human factors increasing the risk of flooding

  Deforestation

  Urbanisation

  Agriculture
• What are the physical factors increasing the risk of flooding

  Precipitation

  Geology

  Relief
• How does deforestation increase the risk of flooding

  Trees are removed which means that much more water is available and transferred rapidly to the river channels

  This is because much of the water that falls on trees is evaporated or stored temporarily on leaves and branches. Trees also use up water as they grow
• How does precipitation increase the risk of flooding

  Torrential rainstorms can lead to sudden flash floods. Steady rainfall over several days can also lead to flooding in lowland river basins

  River chemicals cant contain the sheer volume of water flowing into them so will overfill
• How does urbanisation lead to increase in the risk of flooding

  Building on a floodplain creates impermeable surfaces such as tarmac roads, concrete driveways and state roofs

  This means water is transferred quickly to drains and sewers and then into urban river channels. This rapid movement of water makes flooding mor likely
• How does geology increase the risk of flooding

  Some rocks are permeable and others are impermeable which means that they dont allow water to pass through such as shales and clays. This encourages water to flow overland and into river channels
• How does agriculture effect the risk of flooding

  In arable farming soil is left unused and exposed to the elements for oeriods of time. This can lead to more surface runoff. Surface runoff is increased if the land is ploughed up and down steep slopes as water can flow quickly along the furrows
• How can relief increase the risk of flooding

  The relief of a mountain will change the risk of flooding . A high relief mountain will move the water down quickly. Steep slopes encourage rapid transfer of water towards river channels which increases the risk of flooding
• What is a hydrograph?

  A graph which shows the volume of water flowing along a river

  Shows how discharge rises during a storm reaches its peak and the returns to the normal rate of flow
• Hard engineering strategies which are used to manage floods

  Channel straightening

  Dams and reservoirs

  Flood relief channel

  Embankments
• Describe channel straightening


  when a meandering section of a river is engineered to create a widened, straightened and deepened course. This more efficient course improves navigation and reduces flood risk
• What are the advantages and disadvantages of channel straightening

  disadvantages:

  -when a river is straight velocity is reduced this causes sedimentation of the channel so is more likely to flood

  -visually unattractive, endanger animals, destroy habitats and increased pollution

  advantages:

  -reduces flood risk

  -improve navigation so increased trade

  -insurance costs go down due to lower flood risk
• Example of channel straightening


  In the 19th century a new course was cut across a large meander loop on the River Tees to improve navigation
• Describe Dams and reservoirs

  A dam is a large concrete barrier built across a river to impede its flow. This causes the valley behind the dam to flood , forming an artificial lake called a reservoir
• What are the disadvantages and advantages of Dams and reservoirs

  Disadvantages:

  -Flooding of a valley displaces people

  -interferes with path of migrated fish. Algae often collects behind a dam which deoxygenates water

  -Dam may trigger earthquake

  Advantages

  -boosts tourism (reservoirs are attractive)

  -source of drinking water

  -provides hydroelectric power

  -promotes new habitats

  -highly effective against floods
• Example of Dams and Reservoirs

  Kielder Dam and Reservoir in Northumbland
• Describe a flood relief channel

  An artificially made channel that is designed as a backup channel for a river frequently floods. The newly engineered channel runs roughly parallel to the main river
• What are the disadvantages and advantages of a flood relief channel

  Disadvantages:

  -people living in the path of a relief channel have to be moved. settlements downstream suffer from increased flooding

  -are expensive, need to be maintained and repaired, takes a long time to come into effect

  -look unattractive, habitats disturbed, unreliable habitat

  Advantages:

  -removes the risk of flooding from a designated area

  -value homes increases

  -a more secure environment for setting up business ventures

  -provide new habitats

  -provide areas for modal boating and canoeing
• example of flood relief channel

  The River Exe at Exeter has three relief channels