Chapter 3 Soil Erosion and Its Controls

Watershed management-- 11 3.1 Introduction Soil erosion is the detachment and removal of soil particles from the soil mass by water or wind. 2019/2/15 Watershed management-- 11

Watershed management-- 11 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. 2019/2/15 Watershed management-- 11

Watershed management-- 11 3.1 Introduction Soil erosion rate 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. 2019/2/15 Watershed management-- 11

Watershed management-- 11 3.1 Introduction Classification of erosion by eroding agents Water erosion Wind erosion 2019/2/15 Watershed management-- 11

Watershed management-- 11 3.1 Introduction Classification of erosion by action Rain drops Shallow flows Concentrated flows 2019/2/15 Watershed management-- 11

Watershed management-- 11 3.1 Introduction Classification of erosion by form Sheet erosion Rill erosion Gully erosion Channel erosion 2019/2/15 Watershed management-- 11

Watershed management-- 11 3.1 Introduction Classification of erosion by location Inter-rill erosion Rill erosion 2019/2/15 Watershed management-- 11

General classification of erosion Inter-rill erosion Rill erosion Gully erosion Channel erosion Water Wind Gravity Freezing and thawing erosion Mass movement 2019/2/15 Watershed management-- 11

3.2 Factors affecting erosion Climate R Soil K Topography LS Biological B Engineering E Tillage T 2019/2/15 Watershed management-- 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 2019/2/15 Watershed management-- 11

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. 2019/2/15 Watershed management-- 11

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. 2019/2/15 Watershed management-- 11

Watershed management-- 11 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 2019/2/15 Watershed management-- 11

Watershed management-- 11 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 2019/2/15 Watershed management-- 11