Chapter 3 Soil Erosion and Its Controls

1. Chapter 3 Soil Erosion and Its Controls

2. 3.1 Introduction • Soil erosion is the detachment and removal of soil particles from the soil mass by water or wind. Watershed management-- 11

3. 3.1 Introduction • Geologic erosion is the erosion under natural or undisturbed condition. It is called normal erosion or natural erosion also. • Accelerated erosion is the increased rate of erosion over the geologic erosion brought about by human’s activity. Watershed management-- 11

4. 3.1 Introduction • Soil erosionrate is the gross amount of soil moved by water and wind. • Soil loss is the soil moved off a particular slope or field. • Sediment yield is soil loss delivered to a point under evaluation. Kirkby, M.J. and R.P.C. Morgan. Edited. Soil Erosion, John Wiley & Sons. Watershed management-- 11

5. 3.1 Introduction Classification of erosion by eroding agents • Water erosion • Wind erosion Watershed management-- 11

6. 3.1 Introduction Classification of erosion by action • Rain drops • Shallow flows • Concentrated flows Watershed management-- 11

7. 3.1 Introduction Classification of erosion by form • Sheet erosion • Rill erosion • Gully erosion • Channel erosion Watershed management-- 11

8. 3.1 Introduction Classification of erosion by location • Inter-rill erosion • Rill erosion Watershed management-- 11

9. General classification of erosion Water Wind Gravity Freezing and thawing erosion Inter-rill erosion Rill erosion Gully erosion Channel erosion Mass movement Watershed management-- 11

10. 3.2 Factors affecting erosion • Climate R • Soil K • Topography LS • Biological B • Engineering E • Tillage T Watershed management-- 11

11. 3.3 Measurement of soil erosion • Microplots 1cm2 • Unit plot: 6ft72.6ft = 0.01 acre • Large plots • Small watersheds <1000 km2 <200 km2 <50km2 • Hydrological stations Watershed management-- 11

12. 3.4 Prediction of soil loss • Scientific farm planning for soil and water conservation requires knowledge of the relations between those factors that cause loss of soil and water and those that help reduce such losses. • Controlled studies on field plots and small watershed have supplied much valuable information. Watershed management-- 11

13. 3.4 Prediction of soil loss • Greatest benefits from such research can be realized only when the finding are converted to sound practice. • Specific guidelines are needed fro selecting the control practices. • The soil loss prediction procedure provides such guidelines. Watershed management-- 11

14. 3.5 Soil Loss Tolerances The maximum level of soil erosion that will permit a high level of crop productivity to be sustained economically and indefinitely Watershed management-- 11

15. 3.6 Models of soil erosion • 1940, Zigg, A.W., Degree and length of land slope as it effects soil loss I runoff • 1965, Wischmeier, W.W., Universal soil loss equation • 1978, USLE • 1980, CREAMS—Chemicals, Runoff, and Erosion from Agricultural Management Systems • 1996, WEPP—Water Erosion Prediction Project • 1997, RUSLE—Revised Universal Soil Loss Equation Watershed management-- 11