Erosion: 

Erosion is a three-step process involving the detachment, transportation, and deposition of soil particles. There are many kinds of erosion, including sheet erosion, rill erosion, gully erosion, stream bank erosion, and wind erosion. Each of these types of erosion involves the detachment, transportation, and downstream/downwind deposition of sediment.

 

Sheet Erosion:  The uniform movement of a thin layer of soil across an expanse of land devoid of vegetative cover. Raindrops detach soil particles, which go into solution as runoff occurs and are transported downstream to a point of deposition. Deposition occurs when runoff slows to the point where soil particles can no longer remain in suspension. Tilled agricultural fields and construction sites are subject to sheet erosion.

 

 

Rill Erosion:  When sheet flows begin to concentrate on the land surface, rill erosion occurs. While sheet erosion is generally invisible, rill erosion leaves visible scouring on the landscape. This type of erosion occurs when the duration or intensity of rain increases and runoff volumes accelerate.

 

 

Gully Erosion:  Rill erosion evolves into gully erosion as duration or intensity of rain continues to increase and runoff volumes continue to accelerate. A gully is generally defined as a scoured out area that is not crossable with tillage or grading equipment.

 

 

Stream Bank Erosion:  This type of erosion is the scouring away of stream banks. Degrading or incising streambeds and/or repeated high flows of extended duration cause bank erosion. Bank erosion is significant contributor of sediment loads during high stream flows.

 

 

Wind Erosion:  Wind erosion is similar to sheet erosion in that detachment, transportation, and deposition of soil particles occurs, except that wind is the transportation mechanism rather than water. There are three types of wind erosion:  siltation, suspension, and surface creep. The largest volume of erosion occurs via siltation. Sand size particles move in short hops close to the soil surface. Silt size particles move in longer hops within 12 inches of the soil surface and clay size particles are lifted into suspension and moved into the air.

 

Sediment:  

Sediment is the detached soil particles moving in the erosion process.

 

Erosion Control: 

Understanding the erosion process is essential to the development and implementation of effective erosion control plans. The key to erosion control is preventing the detachment of soil particles and reducing the volume of runoff. This is achieved through the use of practices such as minimizing land disturbing activities and maintaining vegetative covers or substituting for lack of growing vegetation by mulching or applying a compost blanket or erosion control mat.

 

Sediment Control:

Sediment control is trapping detached soil particles that are being transported and ensuring they are deposited on site to prevent damage to other properties or receiving waters. This is achieved by such practices as silt fence installation, compost berms or filter socks, and sediment control basins.

 

Velocity Control:

Velocity control is used to reduce the erosional forces of concentrated flow on a construction site.  Practices include toe slope drains, rock check dams and other check dams, and diversions.

 

Pollution Prevention:

 Pollution prevention includes management of on-site chemicals, concrete washout, sanitary waste, and dust.  All chemical storage containers should have secondary containment.  Spill kits should be on hand for quick response to spills.  Concrete should be washed out in designated areas.  Portable toilets should be on-site and secured to the ground.  Dust suppressants should be used during dry periods.