Soil Erosion and Erosion Control

southern Illinois

~3 ft high

I. OverviewA. One of the most destructive human events on world’s soil resources

I. OverviewA. One of the most destructive human events on world’s soil resources

I. OverviewA. One of the most destructive human events on world’s soil resources

The Dust Bowl (1931-1939)

The Dust Bowl (1931-1939)

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I. OverviewB. Labeled as a pollutant by EPA

II. The Erosion ProcessA. Agents of erosion

II. The Erosion Process B. Natural soil loss as a function of ppt.

Langbein and Schumm, 1958

Effective rainfall refers to the percentage of rainfall which becomes available to plants and crops.

II. The Erosion Process B. Natural soil loss as a function of ppt.

Langbein and Schumm, 1958

II. The Erosion Process C. Effects of Particle Size on Erosion

Hjulstrom,1939

II. The Erosion Process D. Water

Rainsplash

II. The Erosion Process D. Water

Sheet Wash

A. Erosion

Rill Erosion

Gully Erosion

II. The Erosion Process E. Wind

II. The Erosion Process E. Wind

II. The Erosion Process E. Wind

Most common in arid and semi-arid environments

III. Erosion and Land UseA. Agriculture

III. Erosion and Land UseA. Agriculture

III. Erosion and Land UseA. Agriculture

Sediment Supply

Mill Pond Dams

Mill Pond Dams

Mill Pond Dams

Mill Pond Dams

Rates of Denudation (Erosion)Long Term: ~4 cm/1000 yrHistoric: 200 – 1600 cm/1000 yr

III. Erosion and Land UseB. Land Development

Logging

III. Erosion and Land UseB. Land Development

Vice and others, 1069

III. Erosion and Land UseB. Land Development

Wolman and Schick

III. Erosion and Land UseB. Land Development

Table 10-2

III. Erosion and Land UseB. Land Development

Wolman, 1967

IV. Universal Soil Loss EquationA. Overview• Hailed as one of the most significant

developments in soil and water conservation in the 20th century.

• Empirically-derived to estimate soil erosion by raindrop impact and surface runoff.

• Culmination of decades of soil erosion experimentation conducted by university faculty and federal scientists across the United States.

• In use world-wide

IV. Universal Soil Loss EquationB. The Equation

A = RKLSCP

IV. Universal Soil Loss Equation

A = RKLSCPA: Estimated soil loss (tons/acre/yr)R: Rainfall Factor:A statistic calculated from the annual summation of rainfall energy in every storm (correlates with raindrop size) times its maximum 30 - minute intensity.

IV. Universal Soil Loss Equation

A = RKLSCPA: Estimated soil loss (tons/acre/yr)R: Rainfall FactorK: Soil Erodibility FactorQuantifies the cohesive, or bonding character of a soil type and its resistance to dislodging and transport due to raindrop impact and overland flow.

A = RKLSCPL: Slope-Length FactorS: Slope Steepness FactorSteeper slopes produce higher overland flow velocities. Longer slopes accumulate runoff from larger areas and also result in higher flow velocities. Thus, both result in increased erosion potential, but in a non - linear manner. For convenience L and S are frequently lumped into a single term.

“The Topographic Factor”

A = RKLSCPC: Cover FactorThis factor is the ratio of soil loss from land cropped under specified conditions to corresponding loss under tilled, continuous fallow conditions.

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Goal: limit to 5 tons/acre/year

1 Ton of Gravel

IV. Universal Soil Loss EquationA = RKLSCPP: Control Practice FactorPractices included in this term are contouring, strip cropping (alternate crops on a given slope established on the contour), and terracing.

Default Value: set to “1”

IV. Universal Soil Loss Equation

A = RKLSCPA: Estimated soil loss (tons/acre/yr)R: Rainfall FactorK: Soil Erodibility FactorL: Slope-Length FactorS: Slope Steepness FactorC: Cover FactorP: Control Practice Factor

“The Topographic Factor”

LS Factor = ????

LS Factor = ????A = RKLSC

R Factor = 125

K Factor = 0.19

A = RKLSCP

LS Factor = ????L: Slope-Length FactorS: Slope Steepness Factor

= 43.46 tons/acre/yr

C = 0.11

Choosing between Idealism vs. Pragmatism……

V. Estimating “Q” (Discharge)A. The Concept:

V. Estimating “Q” (Discharge)A. The Concept:

The Rational Equation

Qp=CIAWhere Qp=peak flow rate (ft3/s)

C= runoff coeffic. I = ave ppt intensity (in/hr) A = drainage area (acres)

Best for small basins of under 10,000 acres

Qp=CIAWhere Qp=peak flow rate (ft3/s)

C= runoff coeffic. I = ave ppt intensity (in/hr) A = drainage area (acres)

Qp=CIAWhere Qp=peak flow rate (ft3/s)

C= runoff coeffic. I = ave ppt intensity (in/hr) A = drainage area (acres)

“Need to solve “I” using ‘Time of Concentration calculations, and the recurrence interval of the rain storm in question.”

Where K and bare constants foran individual basin

“Kirpick Eq.”

First: solve for timeof concentration (“Duration”);THEN: solve for rainfall intensity fora given X year storm.

“Time of concentration”

First: solve for timeof concentration;THEN: solve for rainfall intensity fora given X year storm.

First: solve for timeof concentration;THEN: solve for rainfall intensity fora given X year storm.

First: solve for timeof concentration;THEN: solve for rainfall intensity fora given X year storm.

Tc = 14.28 min10 yr. storm

“Time of concentration”

First: solve for timeof concentration;THEN: solve for rainfall intensity fora given X year storm.

i = 4.56 in/hr

VI

Determine Average Slope:

= Y factor

First: Determine the parcel areas…….

= ave CN factor

= ave CN factor

L = 4500 ftY = 6.05%

L = 4500 ftY = 6.05%

Determine i for a 10 year storm for the Richmond Area, where tc = 56 minutes:

Determine i for a 10 year storm for the Richmond Area, where tc = 56 minutes:

i = 2.43”/hr for 56 minutes

OR….

“NEW”

C