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 (never touching bottom)
  
  
• saltation - coarser material (like gravel and sand) bounce along
  
  
• traction - larger material dragged along (large rocks)
  
  
  
• degrading streams
  • cutting down, carving and eroding
  • adding to suspended load
  • max. on steeper gradient
  • soft parent material
    
    
• aggrading streams -
  
  • more sediment than it can transport - deposition
  • maximum on flattened landscapes downstream
    • decrease in velocity
    • silt-filled deltas and estuaries
    • Yuba River in Marysville 1870 - hydraulic mining day
      

• Graded streams
  • neither degrading or aggrading ( flowing in equilibrium)
    • striving toward

• three (3) dimensional and complex nature
• gravity must overcome friction from bank walls & bottom
  • most energy is used up by overcoming friction!
  • erosion is limited - (5%) on average
  • faster current is in middle of river (with less friction)
    

• (many more drainage patterns - read in book)
  
  
• straight channels - unusual in nature; often along faulted rock
  
  
• thalweg - stream flow will wander in even the straightest channels
  • likely to transform into a sinuous channel
    • indicating the deepest part of channel
      
      
• meandering channels - sinuous channels with defined loops
  • generally associated with low gradient streams
  • broad floodplains resulting from migrating river
    • Sacramento Valley
      
      
• braided streams - multiple, interwoven channels filled with sediment
  • often broad glaciated streams loaded with silt and gravel
    • Canada and Alaska