Geography- drainage basin

  • Created by: Gina5395
  • Created on: 15-02-19 19:15
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  • Processes that shape fluvial environments
    • Drainage Basin as an open system
      • 3 types of systems
        • Isolated- If nothing transfers in or out across its boundaries  eg. The Universe
        • Closed- If only energy can enter or leave eg water (hydrological) cycle
        • Open- Both material and energy can exit or enter them eg. Drainage Basin
      • DEFINITION: The Drainage basin is an area of land drained by its river and all of its tributaries. The boundary is known as the watershed
      • Inputs- precipitation stores- Interception, surface store, soil moisture store, groundwater store    Transfers- stem flow, infiltration, percolation, overland flow, throughflow, groundwater flow     Outputs- evaporation, transpiration, channel  runoff
    • Storm and annual hydrographs
      • Hydrograph- A graph that shows river discharge and precipitation over time
        • Storm hydrographs show the change in discharge caused by a period of rainfall
          • Features of FLASHY: Steep limbs short lag time high peak discharge flooding likely
          • Features of FLAT:    Gentle limbs long lag time low peak discharge flooding unlikely
        • Annual hydrograph- shows the variation in river discharge over 12 months
        • Factors that influence discharge and the storm hydrograph
          • Nature of the storm- how long the storm lasts, how heavy it is, type of precipitation and direction and speed of rain can impact hydrograph
          • Permanent features
            • Basin size and shape
              • Small Basin- rain gathered and transferred quickly= short lag time+ storm flow
              • Large Basin- Precipitation could take days or weeks to flow through= longer lag time eg Nile/Congo
            • Relief- Steep slopes will shed water more rapidly than gentle slopes = mountainous areas flash floods
            • Soil type- Permeable soils with high sand content = infiltration+ throughflow. This decreases the vol. of surface runoff
            • Geology- Permeable bedrock= percolation which reduces vol. of water stored in the soil + transferred via surface runoff
            • Drainage density- On surface rain drains rapidly if reaches channel quickly. increased drainage density= more efficiently drained
          • Temporary features
            • Previous conditions- state of basin just before storm. recent rainfall= saturated soil drought= depleted groundwater stores= high storage
            • Vegetation Cover- high vegetation= increased evapotranspiration= reduced precipitation transferred by river. In summer, deciduous trees intercept + if it enters soil= taken by roots
          • Land use- human factor
            • Vegetation change- different farming will alter amount+ speed flowing through basin
            • Urbanisation- Afforestation= less flashy Artificial surfaces= flashy replacement of vegetated soil= less permeable eg tarmac Urban areas are highly engineered. Drainage systems= rapid drainage
      • River Discharge is the volume of water passing a particular point at a particular time
        • Discharge = width x depth x velocity

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