soil erosion by water - causes and mitigation
TRANSCRIPT
Soil Erosion By Water -Causes and Mitigation
Jerry J. DaigleState Soil Scientist
Bradley A. StickerAsst. State Conservation Engineer
USDA - Natural Resources Conservation Service
Stormwater Phase II
Soil - Ecological and Hydrological Resourcesupports plant growthprovides waterprovides nutrientsprovides mechanical supportfilters before enteringsurface waterfilters beforeenteringaquifers
Stormwater Phase II
soil FiltersBuffers
Degrades
Detoxifies
Immobilizeswatertable
Soil - Controls the fate of precipitation
controls what part infiltratescontrols what part runs offstores water at depths available for plantstransmits water to underlying materials
Stormwater Phase II
Erosion
Erosion is a process of detachment and transport of soil particles by erosive agents
Ellison, 1944
Stormwater Phase II
Sediment LoadSediment Transport
Detachment
Soil
Rain
RunoffSoil
Infiltration
Deposition:
Soil
Sediment LoadSediment Transport
Deposition
Reduces the sediment loadAdds to the soil massLocal deposition
Surface roughness depressions
Remote depositionConcave slopeStripsTerraces
Stormwater Phase II
ErosionErosive Agents
Raindrop impact
Overland flow of surface runoff from rainfall
Stormwater Phase II
Stormwater Phase II
Erosion is a ConcernDegrades soil resource
Reduces soil productivityReduces soil organic matterRemoves plant nutrients
Causes downstream sedimentationProduces sediment which is a pollutantProduces sediment that carries pollutants
Types of Erosion
Stormwater Phase II
Geologic
natural process
humans can accelerate
Types of Erosion
Stormwater Phase II
Raindrop or Splash
high detachment capacity
low capacity for transport
Types of Erosion
Stormwater Phase II
Interrill (sheet)low detachment capacityhigher capacity for transport
Types of Erosion
Stormwater Phase II
Rillsmall channels <1 foot deeplow detachment capacityhigher capacity for transport
Types of Erosion
Stormwater Phase II
Gullyfrom concentrated storm water flowremoves higher volumes per unit area
Types of Erosion
Stormwater Phase II
Stream Channelhigh volume peak flows may erode streambanks and channels
removes portions of the land surface above and adjacent to the bankcan deliver large volumes of sediment directly into the stream
Types of Erosion
Stormwater Phase II
Mass movement (Landslip)
slides - shear along specific surfaces
flows - viscous,fluid movement
Factors affecting erosion
Stormwater Phase II
Topographyslope gradientoverland flow slope lengthlength of eroding portionsslope shape
Land usecover managementsupporting practices
Climaterainfall - amountrainfall - intensity
Soiltexturemoisturesurface roughness
Simple Uniform Slope
Soil LossSedimentYield
Stormwater Phase II
Sediment Yield = Soil Loss
Stormwater Phase II
Complex Slope
Soil loss
Remote deposition
Sediment yield
Sediment Yield = Soil Loss - Deposition
Complex Slope
Soil loss
Remote deposition
Sediment yield
Soil loss
Stormwater Phase II
Sediment Yield = Soil Loss - Deposition
Local Deposition
Random Roughness:
Ridges-Furrows:
Stormwater Phase II
Sediment Yield = Soil Loss - Deposition
Stormwater Phase II
Deposition
Transport capacity = sediment load
Sediment production less than transport capacity
Deposition because sediment production exceeds transport capacity
Relation of deposition to transport capacity and sediment load on a complex slope
HillslopeTransport capacity
Sediment load
Stormwater Phase II
How Deposition at a Grass Strip Affects Sediment Characteristics
17Primary sand524Large aggreg.
1436Small aggreg.5824Primary silt225Primary clay
After (%)Before (%)Particle class
SDR = 0.2Note how deposition enriches sediment in fines
Stormwater Phase II
Basic PrinciplesSediment load accumulates along the slope because of detachmentTransport capacity is function of distance along slope (runoff), steepness at slope location, cover-management, storm severity (10 yr EI)Deposition occurs where sediment load becomes greater than transport capacity
Stormwater Phase II
Prevention and Reductionfit development to the terraintime disturbance to minimize soil erosionretain existing vegetation whenever feasiblevegetate and mulch denuded areasdivert runoff away from denuded areasminimize length and steepness of slopeskeep runoff velocities lowprepare drainage ways and outlets to handle flowtrap sediment on-siteinspect and maintain control measures
Stormwater Phase II
Soil loss
Remote deposition
Soil loss
Sediment yield
Remote deposition
Soil loss Remote deposition
Terraces
Stormwater Phase II
Strips
Soil lossRemote deposition
Soil loss
Sediment yield
Remote deposition
Stormwater Phase II
Dense grass
Erodible soil surface
Deposition region
Deposition ends where transport capacity = sediment load
Transport capacity
Sediment load
Relationship of Deposition to Transport Capacity and Sediment Load for a Grass Strip
Stormwater Phase II
Why worry about erosion at construction sites?
Stormwater Phase II
Sediment Laden Runoff
Stormwater Phase II
Sediment in Drainage Channels
Stormwater Phase II
Construction Site BMPs
Need to address soil erosion and sediment transportMay be structural and/or non-structural Should be applied according to a plan developed prior to construction start
Stormwater Phase II
Types of Construction Site BMPsErosions control BMPs
prevent the detachment of soil particles and subsequent suspension and transportation in runoff waterfirst and best line of defense
Sediment control BMPs remove a portion of the suspended soil particles from runoff
Stormwater Phase II
Erosion Control BMPsMinimize disturbed areas and preserve existing vegetationTemporary and permanent vegetative establishment of disturbed areasMulching disturbed areasCovering stockpilesStabilized construction site entrancesDivert runoff from disturbed areasVarious combinations of all of the above
Stormwater Phase IIMulching
Seed prior to mulching
Hay or straw @ 1 1/2 to 2 tons per acre
Mechanically anchor with netting or crimper
Blowing Straw Mulch
Stormwater Phase IICommercial Mulch Matting
Wide variety of types for various applications
Apply in accordance with manufacturer’s recommendations
Stormwater Phase II
Commercial Mulch Matting
Stormwater Phase II
Vegetative EstablishmentEstablish vegetation as soon as practical after disturbanceNRCS FOTG Standard - Critical Area Planting (Code 342)
Use appropriate seed mix for time of yearTest soilFertilize and lime according to soil test
Stormwater Phase II
Vegetative Establishment
Stormwater Phase II
Sediment Control BMP’s
Second line of defenseRequire proper installationMaintenance is crucial through out project life
Stormwater Phase II
Sediment Control BMP’s
Silt fencesCheck damsDrain inlet protectionSediment retention basinsOther sediment retention devices
Stormwater Phase II
Improperly Installed Silt Fences
Stormwater Phase IIProperly Installed Silt Fences
Stormwater Phase II
Open Top Gabion Check Dams
Stormwater Phase IITypical Drawing of Hay Bail Check Dams
Stormwater Phase II
Drain Inlet ProtectionRequires monitoring and maintenance
Stormwater Phase IITypical Drawing of Drain Inlet Protection
Stormwater Phase IITypical Drawing of Drain Inlet Protection
Stormwater Phase IITypical Drawing of Drain Inlet Protection
Stormwater Phase II
Sediment Basins
Drainage areaRetention timeTemporary storage volume
Stormwater Phase IITypical Drawing of Sediment Retention Basins
Stormwater Phase IISediment Retention Basins
Stormwater Phase IITypical Drawing of Sediment Retention Basins
Stormwater Phase IICommercially Available Sediment Retention Devices
Stormwater Phase II
Available ResourcesUSDA Natural Resources Conservation Service
www.usda.nrcs.gov
International Erosion Control Associationwww.ieca.org
Stormwater Phase II
Our Soilis
Our Strength