CWR4101: Hydrology

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CWR4101 Hydrology

• Mr. Jeff Earhart
• earhart_at_bhiinc.com
• Evaporation

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Evaporation
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Evaporation

• Standing Water
• Soil Moisture
• Moisture on Plants
• Precipitation

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Evaporation

• Process by which the phase of water is changed
  from liquid to a vapor.
• It occurs at the evaporating surface, the contact
  between water body and overlaying air.

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Evaporation

• Evaporation rate is a function of several
  meteorological and environmental factors
• The two main factors from an engineering
  standpoint are
• Solar energy it provides latent heat of vapor
• Advective energy it is the ability to transport

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Evaporation

• Empirical relationships with climate data
• Pan evaporation
• An evaporation pan is a device designed to
  measure evaporation by monitoring the loss of
  water in the pan during a given time period,
  usually one (1) day.

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Evaporation Mass Balance
DS?
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Evaporation Mass Balance

• Evaporation (E)
• Surface water inflow (SI)
• Surface water outflow (SO)
• Groundwater inflow (BI)
• Groundwater outflow (BO)
• Precipitation (P)
• Initial Abstraction (Ia)
• Rainfall Excess (R)
• Infiltration (F)

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Evaporation Mass Balance
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Transpiration
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Transpiration

• Transpiration is the process by which plants
  transfer water from the root zone to the leaf
  surface, where it eventually evaporates into
  atmosphere.

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Transpiration

• The process by which transpiration takes place
  can be described as follows
• Water is extracted by a plants roots, transported
  upward through its stem and diffused into the
  atmosphere through stoma.

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Transpiration

• Contributing factors
• Moisture available
• Vegetation type
• Vegetation density
• Vegetation health

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Evapotranspiration

• It is the process by which water in the land
  surface, soil, and vegetation is converted into
  vapor state and returned to the atmosphere.
• It consists of evaporation from water, soil,
  vegetative, and other surfaces and includes
  transpiration by vegetation.

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Evapotranspiration

• Mass balance
• Irrigation needs

0
Known
0
0
Known
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Evapotranspiration

• Potential Evapotranspiration (PET) is the amount
  of evapotranspiration that would take place under
  the assumption of an ample supply of moisture at
  all times.
• PET is an indication of optimum crop water
  requirements.

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Calculation of Potential Evapotranspiration

• Assume unlimited moisture supply
• Thornwaites Equation
• ET1.6(10t/TE)a
• Blaney and Criddle Equation
• ET kpt/100
• Page 125