Humans cause most soil erosion when we strip the natural vegetation
from the steeper slopes and don't put back a cover of healthy grass
or other vegetation. That causes the worst erosion. When a slope
must be cleared it is very important to replant some vegetative
cover. It's important also to make the slope into terraces. This
will give the runoff water a longer and slower route to the bottom
of the hill. The slower the runoff flow, the less force the water
will have to erode the hillside.
Heavy rain on a fairly even slope creates "sheet runoff." The water
flows downslope as an even sheet. Any dips in the slope will collect
more runoff water, which will be able to erode more strongly. If
the force of this water is not stopped it will produce a gully (Figure
1). The gully will collect more and more water and cause even
more erosion. In time it will remove the soil down to solid bedrock.