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Overland Flow

Overland Flow. Once rainfall exceeds infiltration, water begins to flow. Clay is hard to pick up due to cohesion. Sand is hard to pick up due to size. Most of the sediment in sheet flow comes from rain detachment. THIS IS WHY COVERING THE SOIL IS SO EFFECTIVE!. R. A. McLaughlin.

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Overland Flow

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  1. Overland Flow • Once rainfall exceeds infiltration, water begins to flow. • Clay is hard to pick up due to cohesion. • Sand is hard to pick up due to size. • Most of the sediment in sheet flow comes from rain detachment. • THIS IS WHY COVERING THE SOIL IS SO EFFECTIVE! R. A. McLaughlin NCSU Soil Science

  2. Rills Starting… R. A. McLaughlin NCSU Soil Science

  3. Flow Along Waterway R. A. McLaughlin NCSU Soil Science

  4. Formation of Rills • Water begins to collect near the top of the slope. • Rills generally deepen downslope. • Flow itself results in erosion. • Headcutting moves upslope. • Sediment comes into the rill from overland flow. R. A. McLaughlin NCSU Soil Science

  5. Rills With Sandy Deposits R. A. McLaughlin NCSU Soil Science

  6. Overland vs. Rills • Studies have shown that both erosion processes are important. • Relative importance depends on soil, slope, and storm intensity. • Rills can carry large materials. R. A. McLaughlin NCSU Soil Science

  7. Gully Formation Overland or Rill Flow R. A. McLaughlin NCSU Soil Science

  8. Gully Formation Nick or depression forms R. A. McLaughlin NCSU Soil Science

  9. Gully Formation Headwall forms R. A. McLaughlin NCSU Soil Science

  10. Gully Formation Scouring at headwall base Headwall retreats by undermining and collapse. R. A. McLaughlin NCSU Soil Science

  11. Gully Formation: Piping Water emerges at slope base, then erodes upslope. Restricting layer forces percolating water along slope. R. A. McLaughlin NCSU Soil Science

  12. Gully After One Storm R. A. McLaughlin NCSU Soil Science

  13. Headwall retreat continues… R. A. McLaughlin NCSU Soil Science

  14. Note Headwall Scouring…Nothing to Stop It! R. A. McLaughlin NCSU Soil Science

  15. Gullies Form Even in Flat, Sandy Soil R. A. McLaughlin NCSU Soil Science

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