- Slides: 23
Natural vs. Accelerated Soil Erosion n n 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.
The Three Processes of Soil Erosion n Detachment n Transport n Deposition
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 is eroded material suspended in wind or water. Sedimentation is the deposition of eroded material.
The Erosion Process Rain hitting the land surface can dislodge Unchecked erosion will significant commonly lead to amounts of pollutants formation of channels Sheet flow overland canreceiving erode slopes The 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 cause catastrophic failure of roads or other facilities.
What can accelerate erosion problems? n n Unrestricted development Removal of surface cover Increased imperviousness (i. e. , paving) that increases runoff Poor stewardship
Construction-related erosion can. . . n n n Cause problems for down slope property owners Create nuisance problems on adjacent streets Clog streams and storm drains
Construction-related erosion can. . . n n Result in turbidity plumes in downstream water bodies Cover sensitive habitat areas with sediment
Pollutant Export During Construction n n Clearing and grading exposes soils Eroded sediment can be transported Also transports nutrients, pesticides, bacteria, organic matter, and toxic substances 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 • direct toxicity to wildlife • lake degradation • filling of navigation channels • impacts to commercial fisheries • 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 water treatment costs • Decreased capacity in conveyance facilities • Higher infrastructure maintenance costs
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