Soil Water Balance

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Soil Water Balance

• Reading Applied Hydrology Sections 4.1 and 4.2
• Topics
• Soil water properties
• Soil water flux
• Soil water balance
• Quotation for today (from Socrates) "There is
  only one good, that is knowledge there is only
  one evil, that is ignorance."Contributed by Matt
  Harold.

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Soil Particle Sizes
Table 1. Size limits (diameter in millimeters) of
soil separates in the USDA soil textural
classification system.
Name of soil separate Diameter limits (mm)
Very coarse sand 2.00 - 1.00
Coarse sand 1.00 - 0.50
Medium sand 0.50 - 0.25
Fine sand 0.25 - 0.10
Very fine sand 0.10 - 0.05
Silt 0.05 - 0.002
Clay less than 0.002


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Soil Texture Triangle
Source USDA Soil Survey Manual Chapter 3
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Soil Water Content
Soil Water Content
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Soil Water Flux, q
q Q/A
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Energy fluxes at Freeman Ranch
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Evaporation (mm/day)
Average 1.1 mm/day
Average 3.1 mm/day
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Soil Water Content
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Soil Water Balance at Freeman Ranch
E
P
0 cm
Net Exchange
10 cm
20 cm
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Soil Water Tension, y

• Measures the suction head of the soil water
• Like p/g in fluid mechanics but its always a
  suction (negative head)
• Three key variables in soil water movement
• Flux, q
• Water content, q
• Tension, y

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