Natural vs. Accelerated Soil Erosion Natural geologic erosion has occurred at a relatively slow rate since the earth was formed. Natural erosion produces about 30% of all sediment in the U. S. Natural geologic erosion has occurred at a relatively slow rate since the earth was formed. Natural erosion produces about 30% of all sediment in the U. S. Accelerated erosion is the increased rate of erosion caused primarily by the removal of vegetation or the alteration of ground contours. This type of erosion accounts for 70 % of sediment in the country. Accelerated erosion is the increased rate of erosion caused primarily by the removal of vegetation or the alteration of ground contours. This type of erosion accounts for 70 % of sediment in the country.

The Three Processes of Soil Erosion Detachment Detachment Transport Transport Deposition Deposition

Erosion Erosion is the process in which, by the actions of wind or water, soil particles are detached and transported.

Detachment Raindrop impact energy is enough to dislodge surface sediments.

Transport Detached soil particles are transported by the energy of water flowing over ground and in channels. Additionally, soil particles in fluid systems (like watercourses and ditches) may also detach unprotected soil particles by physical action.

Sediment Sediment is eroded material suspended in wind or water. Sedimentation is the deposition of eroded material. Sedimentation

The Erosion Process Rain hitting the land surface can dislodge significant amounts of pollutants Sheet flow overland can erode slopes Unchecked erosion will commonly lead to formation of channels The receiving water bears the impact of quantity and quality degradation

Rill Erosion As flow concentrates, small channels begin to form in the soil surface.

Rill Erosion to Gully Erosion

Gully Erosion Gullies are formed when Runoff cuts rills deeper and wider or when flows from several rills come together and form a large channel.

Slope Failure Left unattended, erosion can cause catastrophic failure of roads or other facilities.

What can accelerate erosion problems? Unrestricted development Removal of surface cover Increased imperviousness (i.e., paving) that increases runoff Poor stewardship

Construction-related erosion can... Cause problems for down slope property owners Create nuisance problems on adjacent streets Clog streams and storm drains

Construction-related erosion can... Result in turbidity plumes in downstream water bodies Cover sensitive habitat areas with sediment

Pollutant Export During Construction Clearing and grading exposes soils Clearing and grading exposes soils Eroded sediment can be transported Eroded sediment can be transported Also transports nutrients, pesticides, bacteria, organic matter, and toxic substances Also transports nutrients, pesticides, bacteria, organic matter, and toxic substances Uncontrolled construction site sediment loads can be 35 to 45 tons/acre/year Uncontrolled construction site sediment loads can be 35 to 45 tons/acre/year

In-stream Damages May include: destruction of spawning areas, food sources, habitat destruction of spawning areas, food sources, habitat direct toxicity to wildlife direct toxicity to wildlife lake degradation lake degradation filling of navigation channels filling of navigation channels impacts to commercial fisheries impacts to commercial fisheries reduction of water storage capacities reduction of water storage capacities

Suspended Material Sediment can affect light penetration, channel stability, fisheries & habitat.

Off-stream Damages May include: Increased flood hazards Increased flood hazards Increased water treatment costs Increased water treatment costs Decreased capacity in conveyance facilities Decreased capacity in conveyance facilities Higher infrastructure maintenance costs Higher infrastructure maintenance costs

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