Raindrops detach particles; overland flow carries them away. Concentrated runoff can cut small channels called rills.
Splash erosion begins when raindrops strike exposed soil and detach particles. On a slope, more displaced material tends to move downslope. Impact can also break soil aggregates and contribute to a surface crust that reduces infiltration.
Rainwash removes soil through overland flow across the slope. Shallow unchannelled flow can carry detached particles over a broad area. Where water concentrates, it gains greater local erosive power and cuts small channels: rillwash. Rills can deepen and connect as runoff continues.
Rain intensity, drop size, slope length and gradient affect erosion. Soil texture, aggregate stability and antecedent moisture influence both detachment and runoff. Erosion depends on the supply of loose material as well as the flow's ability to transport it.
Vegetation, litter and mulch can shield soil from raindrop impact and slow water. Roots help bind soil and maintain infiltration pathways. Clearing slopes, leaving soil bare or compacting it with machinery can therefore increase sediment loss. Contour planting, cover crops and well-designed terraces interrupt the route, but poorly maintained terrace drains can concentrate damaging flow.
Distinguish water erosion from mass movement. In rainwash or rillwash, flowing water detaches and carries grains. In a slide, gravity moves a mass along a failure surface. Erosion can remove support and trigger a later slide, connecting the two processes.
Step by step
Detach
Raindrop impacts loosen particles on exposed soil.
Transport
Surface runoff moves particles downslope.
Concentrate
Flow gathers in small channels and erodes rills.
Worked example: A bare plantation track
An illustrative compacted track infiltrates less rain than nearby covered soil. Water concentrates in wheel ruts and carries sediment into a stream. The explanation combines human compaction, reduced infiltration and rillwash rather than simply stating that heavy rain causes erosion.
Watch out for this
Planting trees stops all slope erosion immediately.
Young trees may leave much bare ground. Ground cover, litter, root development, runoff paths and maintenance affect actual protection.
Check your understanding
Which change most directly reduces splash erosion?
- Covering exposed soil with mulch.
- Channelling all runoff into one unprotected ditch.
- Removing litter to expose the soil.