Erosion Control Principles and Practices
The two-part process
Erosion requires detachment and transport. Detachment comes from raindrop impact (splash), flowing water, wind, and freeze-thaw. Water erosion progresses through four stages: splash → sheet → rill → gully. The classic exam distinction: a rill is small enough that ordinary tillage erases it; a gully is not, and requires engineered treatment. Gullies and channel erosion are not addressed by the Universal Soil Loss Equation.
The prediction tool and its limits
RUSLE, A = R × K × LS × C × P, predicts average annual sheet and rill erosion on a slope. It is not an event model, it does not predict gully or streambank erosion, it does not size sediment basins, and it does not estimate sediment delivered to a receiving water - that requires a delivery ratio. Traps: asking which factor a mulch application changes (the C factor), or whether A from RUSLE can be used directly as sediment yield.
The control hierarchy
- Minimize disturbed area and duration.
- Protect steep slopes, channels, and outlets.
- Keep soil covered (vegetation, mulch, blankets, hydroseed).
- Divert and slow runoff (diversions, check dams, slope breaks).
- Trap sediment only as a last line of defense.
Cover is the most powerful single variable: dense, well-established vegetation can cut soil loss by roughly an order of magnitude compared with bare ground.
Rule of thumb
For the LS factor, doubling slope length raises soil loss by about 1.4× (exponent ≈ 0.5); increasing slope steepness from 5% to 10% raises LS by roughly 2× or more. Shorten slopes and flatten where you can - cover and roughness do the rest.