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Unit 1: Landdegradationproblems

Gandhiv Kafle

Lecturer, IOF, Hetauda

WME 508: Soil and water conservationengineering - by Gandhiv Kafle1

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Land & land degradation?

} Land:

} soil resource,

} water,

} vegetation,

} Wildlife,

} landscape, and

} microclimatic components of an ecosystem.} Land degradation: temporary or permanent

lowering of the productive capacity of land

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Causes of land degradation

} Causes of land degradation are the agents

that determine the rate of degradation.

} Biophysical (land use and land

management, including deforestation andtillage methods),

} Socioeconomic (e.g. land tenure, marketing,

institutional support, income), and} Political (e.g. incentives, political stability)

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Process of land degradation

} Physical processes: decline in soil structureleading to compaction, erosion,

desertification, environmental pollution, andunsustainable use of natural resources.

} Chemical processes: acidification, leaching,salinization, decrease in cation retentioncapacity, and fertility depletion.

} Biological processes: reduction in total andbiomass carbon, and decline in landbiodiversity.

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} Land degradation is a major problem inall South Asian countries.

}Degradation caused by water is perhapsthe greatest challenge facing South Asia,as many areas have periods of highrainfall and steep mountainous regions.

}

The steep and fragile landscape &geology of Nepal is susceptible to soilerosion and landslides.

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Estimates of the global extent (in

million km2) of land degradation(Oldeman, 1994)

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Impacts of land degradation

Onsite impacts

}decline in landquality on sitewhere degradationoccurs (e.g.

erosion)

Offsite impacts

} sedimentation ofreservoirs, dams,decline in river water quality, air 

pollution (carbonemission), foodscarcity andmalnutrition

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Water erosion

}Water erosion is the process of detachingthe soil particles from the land surface of

one place and its transportation toanother place for deposition by water.

}Water erosion involves three distinctprocesses: a. Detachment, b.

Transportation and c. Deposition

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Main forms of water erosion

}Splash erosion

}Sheet erosion

}Rill erosion

}Gully erosion

}Streambank erosion

Rills: <1 foot depthSmall gullies: <3 feet depth

Medium gullies: 3-15 feet depth

Large gullies: 15-30 feet depth

Ravines: >30 feet depth

Detachment

Transportation

Deposition

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Water erosion predictionequation

}Universal Soil Loss Equation (USLE; Wischmeier & Smith 1978).

}E = R. K. L. S. C. P} E is the mean annual soil loss (ton ha-1),

} R is the rainfall erosivity factor,

} K is the soil erodibility factor (ton ha-1),} L is the slope length factor,

} S is the slope steepness factor,} C is the crop management factor and

} P is the erosion-control practice factor.

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Wind erosion

}Wind erosion is the erosion of soil by theaction of wind.

} It is caused by the transportation of soilparticles from one place to another through wind.

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Soil movement due to winderosion

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Guess questions}What is land degradation? Why is the

land degradation a serious problem?

}Define water erosion and its mechanism.Describe the types of water erosion.

}Write a short note on water erosionprediction equation.

}Define wind erosion. Indicate its types.

} Soil erosion is a serious problem for the

farming communities of Nepal. Justify it.WME 508: Soil and water conservation engineering -

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