Infiltration Basics: Precipitation Entering the Soil

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Infiltration Basics Precipitation Entering the
Soil

• Definitions and Principles
• Soil Characteristics
• Description

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Component of Hydrologic Cycle
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The Soil System
Precipitation, snowmelt, overland flow,
throughfall
Evaporation
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Soil Texture and Classes
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Bulk Density Differs with Soil Texture and as a
Result of Use
Bulk density is usually a constant property of
soil unless organic matter content changes
(oxidation) or soil is compacted
High Organic Matter Affects Overall Mass
Va decreased
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Soil Water Pressure
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Darcys Law (Saturated Soil)
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Soil Moisture, Hydraulic Conductivity and Soil
Water Pressure
For ?0.5
Air enters pore spaces in place of water
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K, Texture and Relative Saturation
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Hysteresis
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Ink Bottle Effect
r2
F? 2prs(cosa)
r1
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Infiltration Measurement
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Infiltration rate curve
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Estimating Infiltration

• ?(S) ?S-b ?? -b?b S ?/?
• K(S)KsatScKsat ? -c?c c2b3
• b,c gt 1

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Implications

• ?(S) ?S-b S?1, so S-b gt 1

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Infiltration models

• Horton (black box)
• Richards equation (truncated version of a
  process model)

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Horton model
Exponential function
where e 2.71828
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Infiltration rate curve
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Horton model
f0
fc
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Phillips equation
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Variability of infiltration
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Preferential flow
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Point ? watershed???

• Areal-weighted averages

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Point ? watershed
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Watershed size 7.2 km2
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Summary

• Definitions Soil system, texture,
  classification, characteristics (bulk density,
  porosity, degree of saturation, soil moisture
  content, hydraulic conductivity, soil moisture
  release curves)
• Characterization techniques infiltration
  measurement
• Description of infiltration dynamics