1. Chapter 3 Soil Erosion and Its Controls

2. 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

3. 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

4. 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

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

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

7. 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

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

9. 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

10. 3.2 Factors affecting erosion
Climate R
Soil K
Topography LS
Biological B
Engineering E
Tillage T
2019/2/15
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
2019/2/15
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.
2019/2/15
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.
2019/2/15
Watershed management-- 11

14. 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

15. 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