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Saturated Soils Needed

Saturated Soils Needed. Water is initially drawn into soil by gravity and capillary forces. Runoff occurs once the soil is saturated and rainfall exceeds infiltration rates. How quickly this occurs depends on the soil…. R. A. McLaughlin. NCSU Soil Science.

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Saturated Soils Needed

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  1. Saturated Soils Needed • Water is initially drawn into soil by gravity and capillary forces. • Runoff occurs once the soil is saturated and rainfall exceeds infiltration rates. • How quickly this occurs depends on the soil… R. A. McLaughlin NCSU Soil Science

  2. Soil Infiltration Rates Decline Over Time R. A. McLaughlin NCSU Soil Science

  3. Raindrops: The Start of Erosion TIME: 0 sec 1/1400 1/150 1/70 Rain droplet falls on saturated soil. Crater formed Soil is displaced Displaced soil is deposited R. A. McLaughlin NCSU Soil Science From Hillel 1998

  4. Soil is displaced Displaced soil is deposited, farther downslope than upslope Slope Makes Big Difference TIME: 0 sec 1/1400 1/150 1/70 R. A. McLaughlin NCSU Soil Science From Hillel 1998

  5. Actual Droplet Splash on Saturated Soil R. A. McLaughlin NCSU Soil Science

  6. Splash Has Removed Fine Materials, Left Rocks R. A. McLaughlin NCSU Soil Science

  7. Surface Sealing and Crusting • Rain droplets break down aggregates, sort the soil. • Smallest particles form layer on surface. • Infiltration rates decline 10X, often after only one storm. • A crust forms as the soil dries. R. A. McLaughlin NCSU Soil Science

  8. Soil ErodibilityAll Soils Are Not Created Equal • Texture or Particle Size Distribution • Silt is the most easily eroded component. • Clay tends to remain bound in the soil structure. Once caught up in runoff, it is very difficult to settle out. • Sand promotes infiltration, reducing runoff volume, and tends to settle quickly. • Organic Matter: increases infiltration so runoff volumes are lower. R. A. McLaughlin NCSU Soil Science

  9. Soil Erodibility (cont.) All Soils Are Not Created Equal • Structure • Blocky, platy, or massive are less erodible than granular. • Permeability • Rapid is less erodible than slow! R. A. McLaughlin NCSU Soil Science

  10. Creedmoor Sandy Loam Sandy Loam Sandy Clay Loam Clay R. A. McLaughlin NCSU Soil Science

  11. Erodibility Changes With Depth R. A. McLaughlin NCSU Soil Science

  12. Climate, Landscape Position and Parent Material Affect Soil Characteristics Wayah Plott Edneyville-Chestnut Tuskasegee Tuckasegee Dellwood BIOTITE GNEISS GRANITE R. A. McLaughlin NCSU Soil Science

  13. Soil Erodibility (K) Calculation % OM Structure % Silt/Very Fine Sand % SAND Permeability R. A. McLaughlin NCSU Soil Science

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