Natural vs. Accelerated Soil Natural vs. Accelerated Soil ErosionErosion

Natural geologic erosion has occurred at a Natural geologic erosion has occurred at a relatively slow rate since the earth was relatively slow rate since the earth was formed. Natural erosion produces about formed. Natural erosion produces about 30% of all sediment in the U. S.30% of all sediment in the U. S.

Accelerated erosion is the increased rate Accelerated erosion is the increased rate of erosion caused primarily by the removal of erosion caused primarily by the removal of vegetation or the alteration of ground of vegetation or the alteration of ground contours. This type of erosion accounts contours. This type of erosion accounts for 70 % of sediment in the country.for 70 % of sediment in the country.

The Three Processes of Soil The Three Processes of Soil ErosionErosion

DetachmentDetachment

Transport Transport

DepositionDeposition

ErosionErosion

Erosion is the process in which, by the

actions of wind or water, soil particles are detached and

transported.

DetachmenDetachmentt

Raindrop impact energy is enough to

dislodge surface

sediments.

TransportTransport

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.

SedimentSedimentSediment is eroded material suspended

in wind or water.

Sedimentation is the deposition of eroded material.

SedimentationSedimentation

The Erosion ProcessThe Erosion Process

Rain hitting the land Rain hitting the land surface can dislodge surface can dislodge significant amounts of significant amounts of pollutantspollutants

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 ErosionRill Erosion

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

Rill Erosion to Gully Rill Erosion to Gully ErosionErosion

Gully Gully ErosionErosion

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

Slope FailureSlope Failure

Left unattended, erosion can cause catastrophic failure of roads or other

facilities.

Left unattended, erosion can cause catastrophic failure of roads or other

facilities.

What can accelerateWhat can accelerateerosion problems?erosion problems?

Unrestricted development

Removal of surface cover

Increased imperviousness (i.e., paving) that increases runoff

Poor stewardship

Construction-relatedConstruction-relatederosion can...erosion can...

Cause problems for down slope property owners

Create nuisance problems on adjacent streets

Clog streams and storm drains

Construction-relatedConstruction-relatederosion can...erosion can...

Result in turbidity plumes in downstream water bodies

Cover sensitive habitat areas with sediment

Pollutant Export Pollutant Export During ConstructionDuring Construction

Clearing and grading exposes soilsClearing and grading exposes soils Eroded sediment can be transportedEroded sediment can be transported Also transports nutrients, pesticides, Also transports nutrients, pesticides,

bacteria, organic matter, and toxic bacteria, organic matter, and toxic substancessubstances

Uncontrolled construction site Uncontrolled construction site sediment loads can be 35 to 45 sediment loads can be 35 to 45 tons/acre/yeartons/acre/year

In-stream DamagesIn-stream Damages

May include:May include:

• destruction of spawning areas, food destruction of spawning areas, food sources, habitatsources, habitat

• direct toxicity to wildlifedirect toxicity to wildlife

• lake degradationlake degradation

• filling of navigation channelsfilling of navigation channels

• impacts to commercial fisheriesimpacts to commercial fisheries

• reduction of water storage capacitiesreduction of water storage capacities

Suspended MaterialSuspended Material

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

Off-stream DamagesOff-stream Damages

May include:May include:

• Increased flood hazardsIncreased flood hazards

• Increased water treatment costsIncreased water treatment costs

• Decreased capacity in conveyance facilitiesDecreased capacity in conveyance facilities

• Higher infrastructure maintenance costsHigher infrastructure maintenance costs

Before...Before...

……and Afterand After

Before...Before...

……and Afterand After

QuestionsQuestions