NRES 201 Lecture 19 Outline of Last Lecture I. Control of evapotranspirationII. Fundamentals of irrigationIII. Enhancing soil drainageOutline of Current Lecture IV. Significance of soil erosionV. Effects of accelerated soil erosionVI. Mechanics of water erosionVII. Predicting water erosionVIII. Factors affection water erosionCurrent LectureSignificance of soil erosion - - Land degradationo 5 Billion hectares (12 billion acres) degraded in the past half century o Caused by: Desertification due to overgrazing Deforestation Soil Degradation - Acidification, Salinization, Erosiono 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 erosiono Erosion is a natural process that wears down hills and mountains, fills in valleys, lakes, and bays, and transforms soil into sedimento Erosion rates depend on rainfall and type of regolitho Highest rates in semiarid regions Enough rainfall to be erosiveThese 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 vegetationEffects of accelerated soil erosion - - On - site damageso Loss of surface soilo Decline in surface soil quality due to Selective removal of clay and organic matter Structural deterioration - Off - site damageso Sediment deposition that may: smother crops, fill ditches, cover roadwayso Sediment discharge into waterwaysMechanics of water erosion - - Phases of occurrenceo Detachment Separation of particles from the soil masso Transportation Downhill movement of the detached particles by floating, rolling, dragging, and splashingo 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 PracticesFactors affecting water erosion:- Rainfall erosivity factor (R)o Based on regional weather data for: Total amount of rainfall Rainfall intensityo Intense rainfall increases Droplet size and kinetic energy Runoff volumeo Gentle rains cause little erosion And account for low R values in the Pacific NorthwestSoil Erodability - Indicates a soil's inherent susceptibility to erosion- Decreased by greater: Infiltration capacity, Structural stability, Organic Matter
View Full Document
Unlocking...