A soil aggregate is a grouping of individual soil particles and is considered the basic structural unit of soil. When aggregates begin to break down, the soil is in danger of eroding, which proceeds in the following sequence unless interrupted by erosion control measures. The first step in the erosion process is splash erosion. Raindrops strike the earth with considerable energy. Some of the water infiltrates into the soil, while some stays on the surface, saturating the soil and weakening natural soil aggregates so that the impact of subsequent raindrops breaks them down.
Erosion then occurs as dislodged soil particles travel with runoff water.
To see the explosive dislodging effect of rain on soil, just look how far up on a garden stake or building foundation soil material is deposited after a rain. Splashing can start the movement of many tons of fertile topsoil off a slope and into streams and lakes. Therefore, limiting the breakdown of soil aggregates or containing their movement at this stage is important. Sheet Erosion Sheet erosion occurs when rainfall runoff removes the soil surface uniformly over an area. This is difficult to see, because the water, in this case, doesn't cut deep channels when carrying away soil particles.