Rivers Topic

Rivers Topic

Drainage Basin
1. The catchment area from which a river system obtains its water. An imaginary line called the WATERSHED delimits one drainage basin from another.
2. Storm hydrographs
  1. FLASHY
    1. Short lag time
    2. steeper drainage basin
    3. lots of surface runoff
    4. underlying rock
      1. less percolation
    5. urban areas
    6. less trees
      1. less interception
    7. ploughing fields downhill
    8. more tributaries
  2. SUBDUED
  3. Labelling
    1. lag time
      1. the time delay between maximum rainfall amount and peak discharge.
    2. rising limb
      1. As the water enters the drainage basin the discharge rises- there's a delay due to overland flow and interception
    3. base flow
      1. the starting and finishing level
    4. receding limb
      1. shows the fall in the discharge back to the base level
    5. peak discharge
      1. indicates the highest flow in the channel
  4. type of hydrograph is determined by relief, rock and soil type, vegetation, land use, weather, urbanisation, drainage basin density, drainage basin shape and size
3. Long profile
  1. River rejuvenation
    1. significant breaks in slopes (knick points) along a river's long profile- may be due to rejuvenation
  2. illustrates the changes in the altitude of the course of the river from its source, along the entire length of its channel to the river mouth.
  3. UPPER COURSE
    1. LANDFORMS
      1. small waterfalls
        due to change in rock type
      2. rapids
      3. potholes
      4. large boulders
      5. uneven steep river beds
    2. TRANSPORTATION
      1. mostly large boulders
      2. some suspension and little in solution
    3. PROCESSES
      1. hydraulic action, attrition, mostly vertical erosion
    4. DEPOSITION
      1. bedload is too heavy so limited deposition
  4. MIDDLE COURSE
    1. LANDFORMS
      1. rapids
      2. small meanders
      3. small floodplain
    2. PROCESSES
      1. lots of attrition
      2. little hydraulic action
      3. more lateral erosion- start of meanders
    3. TRANSPORTATION
      1. less traction
      2. suspension increases
    4. DEPOSITION
      1. in slow waters
      2. floodplains built in times of flood
  5. LOWER COURSE
    1. LANDFORMS
      1. Large meanders
      2. levees
      3. floodplains
    2. PROCESSES
      1. erosion reduced, just small lateral erosion
        slower waters
    3. TRANSPORTATION
      1. small bedload
      2. mostly suspension
    4. DEPOSITION
      1. mostly fine particles,
        forms levees, slip off slopes and floodplains
  6. BRADSHAW MODEL
PROCESSES
1. EROSION
  1. Hydraulic action
    1. power of moving water removing materials from the channel bed leading to collapsing
  2. corrasion
    1. rubbing actions of material carried along the river bed
  3. corrosion
    1. minerals in rock dissolved by weak acids
  4. attrition
    1. particles striking against one another into smaller pieces
2. TRANSPORTATION
  1. Solution
    1. dissolved particles
  2. suspension
    1. fine materials (sand and silt) carried in water flow
  3. saltation
    1. small stones bounce along the river bed
  4. traction
    1. stones and boulders roll downstream in fast water
3. Deposition
4. Hjulstrom curve
  1. velocity and deposition relationship shows when particles are eroded deposited or transported in relation to particle size

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