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Soil Erosion Processes

Soil Erosion Processes. Richard A. McLaughlin, Ph.D. Soil Science Department North Carolina State University. Water Quality Problems: EPA Ranking. Sediment : widespread problems in surface water. Ruins habitat, clogs waterways, fills lakes and reservoirs.

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Soil Erosion Processes

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  1. Soil Erosion Processes Richard A. McLaughlin, Ph.D. Soil Science Department North Carolina State University

  2. Water Quality Problems: EPA Ranking Sediment: widespread problems in surface water. Ruins habitat, clogs waterways, fills lakes and reservoirs. Nutrients: cause algal blooms and ultimately oxygen depletion. Yuck. Pathogens: local problems especially on coast. Many sources and no way to tell them apart! Organic Stuff: degrades and robs oxygen. Heavy Metals: biological impacts Pesticides: mostly a private well problem. R. A. McLaughlin NCSU Soil Science

  3. Non-Point Pollutant Sources: North Carolina Rivers R. A. McLaughlin NCSU Soil Science

  4. But…Construction Sites Have Highest Erosion Rates R. A. McLaughlin Source: US EPA, 1973 NCSU Soil Science NCSU Soil Science

  5. Erosion: Two Phases • Detachment: individual particles are loosened from the soil mass. • Rainsplash > running water > wind • Transport: water or wind carries the detached particles downslope or downwind. • Flow in rills is the most important. R. A. McLaughlin NCSU Soil Science

  6. Factors in Soil Losses • Rainfall: intensity, duration, and energy. • Soil erodibility: texture, structure, organic matter content. • Topography: slope length, steepness. • Surface Condition: vegetation, mulch, bare, etc. • Erosion Control Practices: contours, terraces, silt fences, basins, etc. R. A. McLaughlin NCSU Soil Science

  7. Factors in Soil Losses • Rainfall: intensity, duration, and energy. • Soil erodibility: texture, structure, organic matter content. • Topography: slope length, steepness. • Surface Condition: vegetation, mulch, bare, etc. • Erosion Control Practices: contours, terraces, silt fences, basins, etc. R. A. McLaughlin NCSU Soil Science

  8. Rainfall Factor • Intensity: the volume of water per unit of time e.g. inches/hour. • Records: 1.23” in 1 minute (MD, 1956), 19” in two hours (WV, 1889), 45” in 3 days (FL, 1950). • Duration: how long the storm lasts. • Norfolk has an average of 603 hours of precipitation/year, or 6.9% of the time. Of that, 12 hours exceed 0.5 in per hour. • Energy: droplet size and velocity. • Heavy rain (0.6”/hr) has 30 times more energy than light rain (0.04”/hr). R. A. McLaughlin NCSU Soil Science

  9. 5.5 5.5 5.0 5.5 6.0 6.0 8.0 7.0 6.0 6.5 8.5 7.0 8.0 24-Hour Rainfall Amounts for a 25-Year Recurrence R. A. McLaughlin NCSU Soil Science

  10. Rainfall Erosivity: Duration + Intensity 175 200 225 250 275 175 300 200 350 250 275 300 350 R. A. McLaughlin NCSU Soil Science

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