Rivers

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  • Created by: lucy
  • Created on: 04-01-13 14:08
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  • Rivers
    • Drainage basin  hydrological  system
      • Inputs
      • stages
      • outputs
    • Water balance
    • Bradshaw  model
    • Drainage basin patterns
      • rectanguler
      • Parallel
      • Radial
      • Dendritic
      • trellised
    • morphometry of basins
    • water budget/balance
    • Hydrographs
      • River discharge
        • rock type
        • temperature
        • soil type
        • basin characteristics
        • precipitation
        • vegetation
        • amount of water already in river
    • Hjulstrom curves
    • channel processes
      • Transport
        • suspension
          • very fine material is carried in the water - most material carried this way
        • solution
          • substances that can dissolve are carried in water
        • saltation
          • larger particles are too heavy to be carried in suspension, instead bounced on river bed
        • Traction
          • very large particles are pushed along bed of river by force of water
      • Erosion
        • Hydraulic action
          • the pressure of water breaks rock particles  away from bed and banks, strongest in rapids, waterfalls and during floods
        • Solution
          • dissolving of rock by chemical processes
        • lateral erosion
        • Attrition
          • eroded rocks smash into each other into smaller fragments, doesn't erode bed/banks
        • vertical erosion
        • Corrasion
          • eroded pieces of rock scrape against the bed and banks removing material, most erosion happens via this
      • deposition
    • wetted perimeter
    • Hydraulic radius
    • mannings equation
    • Graded long profile
      • cross profile
      • Long profile
      • graded profile
    • Landforms of erosion and deposition
      • erosion
        • Rapids
          • several sections of hard rock that create turbulent water
        • Waterfalls
          • from where a band of hard rock meets soft rock, soft rock is eroded leaving a step of hard rock. Water flowing over step speeds up due to lack of friction so gives water greater erosive power = more undercutting of harder rock which can collapse which causes a plunge pool cut out via abrasion to be formed this leads to it retreating and leaving beund a gorge.
        • Potholes
          • small circular hollows in the river bed that are formed by abrasion (corrasion)
        • meanders
          • deposition
            • Levees
              • formed when a river overflows its banks, material is deposited across whole flood plain as river looses velocity - heaviest first closest to river channel = levee
            • Deltas
            • Braiding
              • occurs when rivers carry large amount of eroded sediment. If velocity drops or sediment = to large, deposited on channel, causes river to divide into small winding channels that soon join back into one.
            • Flood plains
          • alternating pools and riffles develop at equally spaced intervals which are 5-6 times the width of river bed. Deeper in pools so more efficient = higher erosive power. spacing between riffles and pools causes max flow to be on one side so turbulence increases = helicoidal flow.
        • Rejuvination
          • vertical erosion
      • deposition
        • Levees
          • formed when a river overflows its banks, material is deposited across whole flood plain as river looses velocity - heaviest first closest to river channel = levee
        • Deltas
        • Braiding
          • occurs when rivers carry large amount of eroded sediment. If velocity drops or sediment = to large, deposited on channel, causes river to divide into small winding channels that soon join back into one.
        • Flood plains
    • Causes and impacts of flooding
      • Human factors
        • flood management strategies
          • Flood management strategies
            • soft engineering
              • river restoration
              • Wetland and river bank consevation
                • river quaggy
              • alteration of urban areas
              • Land use management
                • Abingdon, UK
                  • built on flood plains where 1500 houses = 1% chance of flooding each year.
                    • intense storms - July 2007 where river thames and ock burst banks and 600 properties flooded
                      • hard engineering schemes were rejected as they were too expensive
              • weather forecasts and flood warnings
              • Hollistic
              • Soakways
                • Abingdon, UK
                  • built on flood plains where 1500 houses = 1% chance of flooding each year.
                    • intense storms - July 2007 where river thames and ock burst banks and 600 properties flooded
                      • hard engineering schemes were rejected as they were too expensive
            • hard engineering
              • Levees
              • channel straightening
              • diversion spillways
              • Dams
                • Yangtze river - china
                  • Levees
                  • flows through china and is 6380 km long, 3rd largest river in the world
                    • 1954 flood covered 193, 000 km2 worth of land, killed 33,169 people and 18 million people had to move.
                  • Pros
                    • produces lots of electricity - 22.5 gigawatts  = 3% of chinas demand
                    • reduced risk from once every 10 yrs to once every 100 years
                    • reduction of flooding - safer to navigate and river shipping has increased
                  • cons
                    • destroy habitats and endanger species
                    • dam will trap sediment which could lead to failure of dam and more flooding
                    • dam doesnt protect everyone and increase flooding in tributaries therefore more erosion of riverbanks = collapses and landslides
                    • will flood farmland, 657 factories, 1300 cultural and historic interest.
                    • 1.3 - 2million people wil have to relocate and 13 cities and 1352 villages = submerges
        • agriculture
        • deforestation
        • climate change
        • urbanisation
      • Physical factors
        • high drainage density
        • steep slopes
        • circular drainage basins
        • sparse vegetation or deciduous trees
        • impermeable ground
      • Impacts
        • Economic
        • Social
        • Environmental
      • Carlisle, Cumbria 2005
      • South Asia 2007
    • Flood management strategies
      • soft engineering
        • river restoration
        • Wetland and river bank consevation
          • river quaggy
        • alteration of urban areas
        • Land use management
          • weather forecasts and flood warnings
          • Hollistic
          • Soakways
          • hard engineering
            • channel straightening
            • diversion spillways
            • Dams
              • Yangtze river - china
                • flows through china and is 6380 km long, 3rd largest river in the world
                  • 1954 flood covered 193, 000 km2 worth of land, killed 33,169 people and 18 million people had to move.
                • Pros
                  • produces lots of electricity - 22.5 gigawatts  = 3% of chinas demand
                  • reduced risk from once every 10 yrs to once every 100 years
                  • reduction of flooding - safer to navigate and river shipping has increased
                • cons
                  • destroy habitats and endanger species
                  • dam will trap sediment which could lead to failure of dam and more flooding
                  • dam doesnt protect everyone and increase flooding in tributaries therefore more erosion of riverbanks = collapses and landslides
                  • will flood farmland, 657 factories, 1300 cultural and historic interest.
                  • 1.3 - 2million people wil have to relocate and 13 cities and 1352 villages = submerges

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