erosion & sedimentation processes - ak-cesclak-cescl.com/files/pdf/2_processes.pdf · Ø gully...
TRANSCRIPT
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