NRES 201 Lecture 19 Outline of Last Lecture I Control of evapotranspiration II Fundamentals of irrigation III Enhancing soil drainage Outline of Current Lecture IV Significance of soil erosion V Effects of accelerated soil erosion VI Mechanics of water erosion VII Predicting water erosion VIII Factors affection water erosion Current Lecture Significance of soil erosion Land degradation o 5 Billion hectares 12 billion acres degraded in the past half century o Caused by Desertification due to overgrazing Deforestation Soil Degradation Acidification Salinization Erosion o A downward spiral Begins with a loss of natural vegetation Intensifies as bare soil erodes with a loss of Productivity Residues Organic Matter Culminates in Environmental degradation Soil decline Geological erosion o Erosion is a natural process that wears down hills and mountains fills in valleys lakes and bays and transforms soil into sediment o Erosion rates depend on rainfall and type of regolith o Highest rates in semiarid regions Enough rainfall to be erosive These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute But not enough to support dense protective vegetation Effects of accelerated soil erosion On site damages o Loss of surface soil o Decline in surface soil quality due to Selective removal of clay and organic matter Structural deterioration Off site damages o Sediment deposition that may smother crops fill ditches cover roadways o Sediment discharge into waterways Mechanics of water erosion Phases of occurrence o Detachment Separation of particles from the soil mass o Transportation Downhill movement of the detached particles by floating rolling dragging and splashing o Deposition Accumulation of the transported particles at some place lower in elevation Predicting water erosion o A R K K LS C P A Predicted annual soil loss R Rainfall erosivity K Soil Erodability L Slope length S Slope Gradient or Steepness C Cover and Management P Erosion Control Practices Factors affecting water erosion Rainfall erosivity factor R o Based on regional weather data for Total amount of rainfall Rainfall intensity o Intense rainfall increases Droplet size and kinetic energy Runoff volume o Gentle rains cause little erosion And account for low R values in the Pacific Northwest Soil Erodability Indicates a soil s inherent susceptibility to erosion Decreased by greater Infiltration capacity Structural stability Organic Matter Content
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