Dilute (fluid dominated) Transport

• what are fluid dominated flows?

  particles of solid material carried along by fluid motion, but the space filled by the flow is predominantly occupied by the interstitial fluid
• give three examples of fluid dominated flows?

  wind blown sand, suspended sediment transport in rivers and seed dispersal
• what are the six types of transport?

  carried along the bed, friction drag, form drag, fluid suspension transport, turbulence keeping particles suspended and saltation transport
• what is the force called which acts in the same direction as the direction of flow?

  drag
• what is the force called which acts perpendicular to the direction of flow?

  lift
• what are the two stresses which result in drag?

  pressure stress and shear stress
• what are the two causes of bedlam trasnport?

  friction drag or form drag
• what is suspended load trasnport?


  being lifted into the fluid
• what is suspension caused by?

  lift forces
• what is saltation trasnport?

  a transitional state between bedload and suspended load
• why do particles bounce along the bed during salutation transport?

  flow cannot quite maintain particles in suspension, but the shear stress is too strong to allow the particles to remain at rest on the bed
• what does the x axis of a histogram diagram show?

  particle size in mm
• what does the y axis of a histogram diagram show?

  velocity of the river in cm per second
• what are both axes on a histogram diagram?

  logarithmic
• why do particles need a high velocity to move them?

  as they stick together, making them difficult to split and unload and because there is always a boundary layer
• what does the difference between the force of weight pulling the particle down and the force of buoyancy keeping it afloat determine?

  if the particle will rise up or fall down and the speed at which it rises and falls
• particles will only remain in fluid flow if they are ...?

  lighter than the fluid
• what will happen if the density of the particle is higher than the density of the air or the fluid?

  it will be deposited
• what is required to stop deposition of the particle from the fluid flow from occuring?

  turbulence
• what is the downstream fining of sediments in rivers?

  you find large particles upstream but not downstream as they are dropped off before they move downstream
• what is sediment focusing in lakes?

  large pebbles are found along the coast as they are dropped off, whereas fine sediments are moved out to the middle of the lakes