W8, Erosion

Question 1

Describe some forms of water erosion.

Answer 1

→ Interrill/sheet/splash erosion

→ Rill erosion

→ Gully erosion

→ Tunnel erosion

→ Bank erosion

Question 2

What are the 3 phases of water erosion?

Answer 2

→ Detachment
→ Transport
→ Deposition

Question 3

What are the factors of the Universal Soil Loss Equation (USLE)?

Answer 3

Erosion (A) = Erosivity * Erodibility
= R * (K * LS * P * C)

→ Erosivity, R
= Rainfall/irrigation characteristics
= Not necessarily manageable
▪︎ Total annual amount (mm /yr)
▪︎ Temporal distribution (all at once, over a certain period, regularly throughout year)
▪︎ Intensity (mm /hr)
- Max intensity more important than average intensity
▪︎ Kinetic energy
- Intensity of rainfall (J/m² or J/m²/mm)
- Droplet size (increases with intensity)

→ Erodibility, KLSP*C
= Manageable to varying degrees
▪︎ K = Physical characteristics
- Not very manageable
▫︎ Texture
▫︎ Structure and structural stability
▫︎ Surface structure
↑ infiltration = ↓ K
↑ aggregation = ↓ K
↑ SOM = ↓ K
↑ disturbance = ↑ K
▪︎ LS = Slope length
↑ Ls = ↑ water movement speed = ↑ erosion
↓ Ls = ↑ retention time = ↑ absorption opportunity
↓ run-off velocity = ↑ deposition of eroded material
▪︎ P = Conservation practices
= 1 unless the following are used:
▫︎ Contour banks
▫︎ Contour plowing
▪︎ C = Plant cover
= 1 for fallow or fields plowed up/down the slope
≈ 0.004 for good pasture
▫︎ Depends on crop, rotation, tillage, timing