DEFINITION

Soil erosion is the process by which the land surface is worn away by the action of natural forces such as wind, water, ice, and gravity. It is caused when sediments are detached from the soil mass, transported primarily by flowing water or wind, and eventually deposited as sediment. Water erosion is caused when raindrops falling on bare or sparsely vegetated soil detach soil particles. Water flowing over the ground picks up the particles and carries them. As the runoff gains velocity, it forms channels and detaches more soil particles. This action cuts rills and gullies into the soil, adding to the sediment load. Wind erosion is caused by by winds blowing across unvegetated, disturbed land.

Sedimentation is the settling out of soil particles transported by water and wind. It occurs when the velocity of water in which the particles are suspended is slowed to a sufficient degree, and for a sufficient period, to allow the particles to settle out of suspension.
(Source: Florida Department of Environmental Protection)

Erosion and sediment control go hand in hand. As mentioned above, erosion is the wearing away of soil on the earth's surface by either wind or water. Sediment control is capturing soil that has been removed through erosion.

There are two ways to accomplish sediment control, structural or non-structural means. Structural methods involve constructing a man made structure (i.e. silt fence, sediment traps, check dams, etc...) to collect soil that has been worn away by erosion. Non-structural meathods are intended to prevent erosion of soil in the first place. They include minimizing land disturbance, temporary vegetative cover, mulch, floodplain protection, public education, etc...

The more you can prevent erosion, the less sediment that has be collected and disposed of.


AKA
accelerated erosion, natural erosion, geologic erosion, sediment deposition

RELATED FUNCTIONS

Erosion has both physical and biological impacts.
Excessive quantities of sediment result in costly damage to aquatic areas and to private and public lands. The obstruction of stream channels and navigable rivers by masses of deposited sediment reduces hydraulic capacity. This, in turn, causes an increase in flood crests, resulting in flood damage. Sediment fills stormwater conveyances and plugs culverts and stormwater systems, necessitating frequent and costly maintenance.
The biological effects of sedimentation are even more critical. The presence of fine grained sediments (clays, silts, and fine sands) in an aquatic system reduces both the kinds and the amounts of organisms present. Sediments alter the aquatic environment by screening out sunlight and by changing the rate and the amount of heat radiation. This light reduction inhibits photosynthesis, leading to a decline in benthic plant growth. Consequently, the food chain is disrupted, and the population of consumer species is reduced.
(Source: Florida Department of Environmental Protection)

PERFORMANCE CRITERIA

Erosion is measured in tons/acre/year.


ILLUSTRATION
Many illustrations exist that depict the various mechanisms of erosion (water & wind).

This illustration shows the general concept of erosion, regardless of cause.



CASE STUDIES

The Environmental Protection Agency, as well as most of the states, have realized the importance of erosion control. The National Pollutant Discharge Elimination System (NPDES) Stormwater Program has been established to manage erosion and sediment control from land disturbance activities.
However, in some cases (some states and Native American reservations), the Environmental Protection Agency administers the program.

ADDITIONAL RESOURCES

FLORIDA STORMWATER EROSION AND SEDIMENTATION CONTROL INSPECTOR’S MANUAL