Water

Water erosion is most likely to occur on bare, unprotected soil and results in sheet, rill, and gully erosion. The three main processes of particle movement during water erosion are similar to those of wind erosion and depend on the particle size.

Suspension - clay and fine organic matter

Raindrops dislodge fine particles, which become suspended in the film of water at the surface. Subsequent raindrops further agitate the fine particles, keeping them in suspension.

Bed load - coarse sands

Impact from rain and other particles, along with the force of water flow, sets these larger particles rolling along the soil surface.

Saltation - fine sand and silt

Raindrop impact dislodges larger particles, which are then bounced along in the overland flow, further dislodging more particles.

Types of Water Erosion

Sheet erosion

What appears as uniform removal of thin layers of soil on sloping land is actually minute rilling.

Rill erosion

Removal of soil from small, well-defined channels. Rills are small enough to be "removed" by tillage but account for the greatest amount of soil loss.

Gully erosion

Gullies are larger than rills and cannot be tilled. Gullies further develop by waterfall erosion at the channel head, erosion along the channel, and mass movement of soil from the gully walls.

Methods to Manage Water Erosion

Stubble mulching and trash retention:

Stubble left on the surface of the soil from the previous crop reduces erosion by reducing the impact of falling raindrops and slowing the overland flow of water.

If vegetation cover is reduced below a critical level, soil erosion drastically increases. For example, erosion increases dramatically if ground cover falls below 70% in a grazed pasture.

Grassed waterways:

Grassed waterways go hand-in-hand with contour banks. They are designed to accept runoff captured by contour banks and channel it to a disposal area such as a dam or creek.

Because they carry large volumes of runoff, they need to be permanently grassed and well-managed to avoid being eroded themselves.

Contour banks:

Contour banks reduce erosion by effectively reducing the length of the slope. The runoff water is channeled to a safe disposal area, usually a grassed waterway.

Contour banks are designed to cope with most storm events. However, very severe storms have the potential to overtop the bank, creating a worse problem.

Not farming steeper slopes:

Avoiding tillage of erosion-prone areas, such as steep slopes, reduces not only the problem of erosion on the steep slope but also minimizes runoff to downslope areas.

Grazing is an alternative land use in some areas.

Strip cropping:

Strip cropping alone can be used to minimize soil erosion when slopes are less than 1% and can be used at higher slopes in conjunction with other management practices.

Strips less than 100 m wide, which roughly follow the contour, are laid out on the farm.

Each strip is assigned a different crop in a rotation planned so that no adjacent strips will be fallow at the same time.

Strip cropping is effective because runoff moving through the vegetated strips is slowed down.