EROSION&SEDIMENTATIONPROCESSES

PhotobyNASAJanuary2017

2.ErosionandSedimenta6onProcesses

Goalofthissec3on:Learnthedefini6onsandeffectsofthedifferenttypesoferosion:

TypesofWaterErosionTypesofWindErosion

SOIL EROSION – A natural process by which the land surface is worn away by the action of wind, water, and gravity

ModifiedCourtesyFloridaDEP

Construc6onSiteErosion

Ø  Erosion-Theprocessinwhich,bytheac6onsofwindorwater,soilpar6clesaredisplacedandtransported.

Ø  Sediment-Erodedmaterialthatissuspendedinwaterorwind

Ø  Sedimenta6on-Thedeposi6onorseElingoferodedmaterial

Ø  Turbidity-Themeasureoftherela6veclarityofaliquid(muddiness)

*MeasuredinNTU’sorTransparency

Ø  Raindrop-Movementofsoilpar6clescausedbythedirectimpactofraindropsonbaresoil

Ø  Sheet-Runoffwhichflowsoverthegroundsurfaceasathin,evenlayer

Ø  Rill-Asmall,intermiEentwatercoursewithsteepsides,usuallyonlyafewinchesdeep

Ø  Gully-Achannelcausedbyconcentratedflowofsurfaceandstormwaterrunoffoverunprotected,erodiblesoil

Ø  Stream&ChannelBank-Bankandbederosionofexis6ngstreamchannelcausedbyincreasedpeakflows

TypesofErosion

RaindropImpactErosion

Source:EnvironmentalSoilPhysics,Hillel

+ Surfacesbecome“puddled”+ Lowerinfiltra6onrates+ Increasedrunoff=IncreasedTurbidity

RaindropImpact

SheetFlowErosion

Sheetflowiseasytoseeonpavement

“Shiny”DirtisSheetFlow

RILLEROSIONONACUTSLOPE

RillsturningintoGullies

RillErosion

GullyErosion

EffectsofSoilChange&ImproperTracking

StreambankErosion

EffortstoCorrecttheProblems$$$$$$$

Raindrop

Ø BedLoad-Soilpar6clesthataredragged,rolled,skipped,orsaltated

Ø Suspension-Soilpar6clesthatareliZedupbytheflowenergyandmovedlongdistancesdownstreambeforeseElingtothebed

Ø ColloidalSuspension-Sameassuspensionbutincludesonlythefine,colloidalsoilpar6clesthatmayneverseEletothebed

WaterErosion

StreamBankAZerMi6ga6on

Mi6ga6onAZerHeavyFlowsCreatedStreamBankErosion

Sedimenta6on

SurfaceAreaRequirementsofSedimentTraps

Size mm

Particle Settling Velocity ft/sec

Settling Velocity m/sec

Surface Area ft.2 per ft3/sec discharge

Surface Area m2 per m3/sec discharge

0.5 Coarse sand 0.19 0.058 6.3 20.7

0.2 Medium sand 0.067 0.020 17.9 58.7

0.1 Fine sand 0.023 0.0070 52.2 171.0

0.05 Coarse silt 0.0062 0.0019 193.6 635.0

0.02 Medium silt 0.00096 0.00029 1250.0 4101.0

0.01 Fine silt 0.00024 0.000073 5000.0 16404.0

0.005 Clay 0.00006 0.000018 20000.0 65617.0

1 CFS = 450GPM For every 450 GPM You need 5000SF of pond surface to settle fine silt.

Fine Silt will only fall out slowly, very slowly.

*Pore Size of Silt Fence. The smaller the particle, the bigger the settling basin. Will it fit in your ROW?

DiameterOrderofSizeDiameterOrderofSize SettlingVelocitySettlingVelocity TimeRequiredtoTimeRequiredto

((mm)mm) (mm/sec)(mm/sec) Settle1Meter(3.28ft)Settle1Meter(3.28ft)

®® 10.010.0 GravelGravel 1,0001,000 1.0Seconds1.0Seconds

®® 1.01.0 100100 9.8Seconds9.8Seconds

®® 0.60.6 CoarseSandCoarseSand 6363

®® 0.3*0.3* 3232

®® 0.2*0.2* 2121 48.0Seconds48.0Seconds

®® 0.15*0.15* FineSandFineSand 1515 67.0Seconds67.0Seconds

®® 0.100.10 88 125.0Seconds125.0Seconds

®® 0.060.06 3.83.8

®® 0.0150.015 0.350.35 47.6Minutes47.6Minutes

®® 0.0100.010 SiltSilt 0.1540.154 107.0Minutes107.0Minutes

®® 0.0050.005 0.03850.0385 7.2Hours7.2Hours

®® 0.0030.003 0.01380.0138 20.1Hours20.1Hours

®® 0.00150.0015 C layC lay 0.00350.0035

®® 0.0010.001 0.00150.0015 180.0Hours180.0Hours

®® 0.00010.0001 0.00001540.0000154 754.0Days754.0Days

®® 0.000010.00001 ColloidalParticlesColloidalParticles 0.0000001540.000000154 207.0Years207.0Years

*Rangeofacceptableporesizesforsiltfencegeotextiles.*Rangeofacceptableporesizesforsiltfencegeotextiles.

SOILPARTICLESETTLINGTIME

4 acres needs ½ Acre of pond

for 4 micron particles

ItisDifficulttoTreatFineSilts&ClaysSuspendedinWater

WindErosion

WindErosion