GEO Chapter 16

• Stream


  Any channeled flow of water
• Overland flow


  Unchanneled downslope movement of water
• Valley


  Drainage system is clearly established
• Interfluve


  Higher land that separates adjacent valleys
• Drainage Basins (watershed)


  All area that contributes to overland flow, streamflow, and groundwater
• Divide


  Separate drainage basins
• Scales of divides


  • Small scale - ridge that separates 2 small gullies on a hillside
  • Large scale - continental divide splits huge basins
• Types of stream flow


  • Perennial flow
  • Ephemeral flow
  • Intermittent flow
• Perennial flow


  Water is present all year but fluctuating amount
• Base flow


  Groundwater that seeps into stream channels below the water surface, sustains perennial streams during low precipitation
• Stream ordering


  Technique to describe a stream and its drainage basin
• Stream order


  • First-order stream
  • Second-order stream
  • Third-order stream
• 2 Streams of a given order need to combine to create a stream of the next highest level
• Surface runoff


  Overland flow that starts as melting ice or snow, spring, or rain
• Infiltration


  Water soaking into ground
• Infiltration capacity


  Amount of water that can enter pore space
• Types of surface runoff


  • Sheet wash
  • Rills
  • Gullies
• Stream velocity


  Streams ability to erode and transport material is related to its flow velocity
• Factors that determine stream velocity


  • Gradient or slope
  • Channel shape and size
  • Channel roughness
• Discharge


  Volume of water flowing past a certain point in a given unit of time
• Longitudinal


  Cross-sectional view of a stream from head (source) to mouth
• Factors that decrease downstream


  • Gradient decreases
  • Channel roughness decreases
• Factors that increase downstream


  • Discharge increases
  • Channel size increases
  • Velocity increases
  • Sediment size decreases
• Stream load


  Sediments being transported by a stream
• Stream competence


  Maximum size or rock particles that a given stream can transport
• Stream capacity


  Total amount of load (measured as weight per time)
• If velocity doubles, sediment load may go up 6–8 times
• Fluvial erosion


  Removal of rock material by flowing water, both chemical and physical removal
• Degradation


  Net erosion - lowering of landscape
• Aggradation


  Net deposition of sediments - building up of landscape
• Types of stream load transport


  • Dissolved load
  • Suspended load
  • Bed load
• Saltation


  Heavier particles "bounce" along stream bed
• Traction


  Heaviest particles are pushed or rolled along the bottom
• Stream's ability to carry dissolved load is not affected by velocity
• Base level


  Lowest point a stream can erode down to, sea level is absolute or ultimate base level
• Rejuvenated landscape


  New uplift
• Entrenched landscape


  Stream terraces, remnants of previous valley floors
• Alluvium (fluvial deposits) will be well sorted, water sorts particles by size - heaviest dropped first
• Straight channels


  Short and uncommon, indicate control of rock structure
• Meandering channels


  Intricate pattern of smooth curves, occurs when land is flat, gradient is low