FLUVIAL PROCESSES

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FLUVIAL PROCESSES

• J. David Rogers

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Part 1

• THE WATER CYCLE
• and
• WATER BALANCE

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• Concepts of the hydrologic cycle, upon which
  water balance assessments are normally made

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WATER BALANCE EQUATION

• P R I If ET
• P Precipitation. Most precipitation occurs as
  rain, but also includes snow, hail, fog drip, and
  sleet.
• R Surface runoff (water) from rainfall,
  snowmelt, or other sources, which flows over the
  land surface
• I Infiltration is that portion of the
  precipitation and runoff which infiltrates into
  the vadose zone, below the ground surface or
  stream bed
• If Interflow is the name given to lateral flow
  within the vadose zone which eventually
  exfiltrates as spring flow
• ET Evapotranspiration is the sum of evaporation
  and plant transpiration into the atmosphere

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• Groundwater withdrawal can interrupt the natural
  water balance, causing water tables to lower if
  more water is withdrawal exceeds recharge

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• A typical glimpse of water balance factors,
  without specifying interflow or transpiration
  losses

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• Potential Evapotranspiration loss for the
  continental United States on November 15, 2006,
  in units of 0.01 inches of water.

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• A typical plot of mean annual precipitation
  versus potential evapotranspiration, in this
  case, from central Michigan. These plots are
  useful for gauging irrigation demands

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Vadose Zone(Unsaturated Zone)

• The zone between land surface and the water table
  within which the moisture content is less than
  saturation (except in the capillary fringe) and
  pressure is less than atmospheric. Soil pore
  space also typically contains air or other gases.
  The capillary fringe is included in the vadose
  zone.

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Stage Changes

• When precipitation and channel flow increase,
  this is known as a rising stage
• When this occurs groundwater seeps into the
  channel, creating an influent condition, sketched
  at left.

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• Desert species even suffer transpiration losses.
  Xerophytes and Phreatophytes are contrasting
  species of vegetation in arid regions. The term
  xerophyte describes a plant that has structural
  and physiological adaptations which enable them
  to survive, or even thrive, in areas with very
  little free moisture. Desert phreatophytes are a
  complex group of species with varied adaptive
  mechanisms to tolerate or avoid drought. They
  have the ability to tap a falling water table.