Erosion by Streamflow

Once surface flow is channelized hydraulic power gravity (steep gradient) turbulence When all factors are high - erosion is highest mountains and floods Sierra Nevada Story

Transportation and Deposition

• attrition - natural sizing, rounding and sorting
  • large boulders to fine, suspended silt
  • less sorted to well-sorted
    
    
    
• dissolved load - invisible minerals dissolved in solution
  
  
• suspended load - fine particles (silt) are suspended
  
  
• saltation - coarser material (like gravel and sand) bounce along
  
  
• traction - larger material dragged along (large rocks)
  
  
  
• degrading streams - eroding
  • cutting down
  • often on steeper gradient
    
    
• aggrading streams - depositing
  
  • low gradient (flat), decreased velocity
  • more sediment than it can transport
    • silt-filled deltas and estuaries
    • hydraulic mining day- Yuba River in Marysville 1870s
      

• Graded streams
  • neither degrading or aggrading ( flowing in equilibrium)
    • cutting on outside, depositing on inside

• three (3) dimensional and complex nature
  • gravity must overcome friction from bank walls & bottom
    

• straight channels - unusual in nature; often along faulted rock
  
  
• meandering channels - sinuous channels with defined loops
  
  
• thalweg - indicating the deepest part of channel
  • stream flow will wander in even the straightest channels
• likely to transform into a sinuous channel
  
  
• braided streams - multiple, interwoven streams filled with sediment
  • within main stream channel
  • often broad streams loaded with silt
    • Canada and Alaska