River Transportation and the Hjulstrom Curve

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River Transportation and the Hjulstrom Curve

  1. 1. River Transportation
  2. 2. Load The word load is used to describe the rock particles that are carried by a river. There are three categories: Bedload – large particles carried only at times when the river has much energy. Suspended load – small particles that can be carried by the water, making it look muddy. Dissolved load – minerals carried by solution that are not visible.
  3. 3. A river obtains its load from two main sources: About 90% comes from the movement of material down the slopes of the river valley by weathering and mass movement. 10% comes from the erosion of the bed and banks of the river channel.
  4. 4. <ul><li>The ability of a river to transport depends on: </li></ul><ul><li>Location and supply of material </li></ul><ul><li>Amount of material available </li></ul><ul><li>Character of the material </li></ul><ul><li>Volume of water </li></ul><ul><li>Amount of energy available to do the work. </li></ul>
  5. 5. River capacity – the total amount of load that a river can carry at any one time. Capacity increases as discharge increases. River competence – the maximum size or weight of material a river can transport. In times of flood, a river’s competence will increase – it will be able to carry bigger particles. Capacity and competence increase downstream, as discharge increases, and during times of flood.
  6. 6. Processes of River Transportation Traction – large boulders are rolled along the river bed. Saltation – pebbles, sand and gravel bounce along the river bed. Suspension – fine particles are carried by the water, making the river look muddy. Solution – minerals that are dissolved in the water, and therefore not visible.
  7. 7. The Hjusltrom Curve
  8. 8. The Hjulstrom curve is a graph that shows the relationship between the velocity of a river and the particle sizes that may be transported. It shows the velocity needed to pick up material of a certain size (velocity needed for erosion to take place), and the settling velocity when deposition will occur.
  9. 9. Particles eroded Particles deposited Particles transported

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