10. Soil Erosion

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Slope water follows three pathways:
1. Groundwater flow 2. Overland flow (Hortonian overland flow and Saturated overland flow) 3. Shallow surface storm flow
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Soil erosion process
Rainsplash, slope splash and wind erosion
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Rainsplash. Primary effects:
Formation of an impact crater and splash back transport.
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Rainsplash. Secondary effects:
1. Detachment of particles for slope wash 2. Increases slope wash turbulence 3. Compacts soil-decreased infiltration
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Raindrop impact:
Formation of soil crater and soil splash back
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Factors affecting rain splash
1. Gradient 2. Soil texture and grain size 3. Frequency and Intensity of rainfall 4. Vegetation cover
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Particle displacement is proportional to sin aK where a is gradient and k reflects grain size
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Frequency and intensity of rainfall
Effectiveness depends on kinetic energy of raindrop. Rainfall intensity > 25mm per hour required.
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Rainsplash process:
Rainsplash directly moves only particles > 50mm in size, but larger clasts may be undermined by rainsplash, sometimes forming huge pillars here large boulders shelter underlying fine soil.
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Rainsplash erosion creates
Slopes with convex crusts.
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Slope-wash processes
1. Sheet wash - un-channeled wash 2. Rill wash: channeled wash
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Factors affecting slope-wash
1. Topography 2. Soil depth, permeability, and texture 3. Frequency of intense rainstorms 4. Vegetation cover
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Bare soil and erosion
Bare soil experiences 100-100,000 times more erosion that vegetated soil.
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Vegetation limits slope wash in 5 ways:
1. Increased soil permeability 2. Root mat binds soil 3. Stems interrupt flow 4. Reduces rainsplash turbulence 5. Some precipitation is retained by vegetation
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Velocity reflects:
Gradient and distance from divide
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Accelerated soil erosion
Mainly caused by removal or degradation of vegetation cover due to tillage, deforestation, burning, overgrazing and trampling.
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Consequences of depleted soil erosion
Depletion of topsoil , Rill and gully formation
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Extensive tracts of heavily eroded, uncultivable land with little vegetation
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Traditional (labour intensive) measures of soil conservation:
1. Terracing 2. *****-cropping
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Conventional measures of soil conservation:
1. Contour ploughing 2. Mulch spreading 3. Return of eroded soil to top of slope
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Card 2


Soil erosion process


Rainsplash, slope splash and wind erosion

Card 3


Rainsplash. Primary effects:


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Card 4


Rainsplash. Secondary effects:


Preview of the front of card 4

Card 5


Raindrop impact:


Preview of the front of card 5
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