Principles of Wind Erosion
Wind erosion is the process by which soil particles are detached, transported, and deposited by wind. This phenomenon is particularly common in arid and semi-arid regions where soils are dry, loose, and easily blown away by wind. The primary principles involved in wind erosion are as follows:
- Soil Detachment: The wind exerts a force on the soil particles. The velocity of the wind must be sufficient to overcome the cohesive forces between soil particles. Once the wind speed reaches a critical level, soil particles are detached from the surface.
- Saltation and Suspension:
- Saltation refers to the hopping or bouncing of particles over short distances.
- Suspension involves smaller particles (like silt and clay) being carried by the wind over longer distances.
Saltation is the dominant form of particle movement in wind erosion and is responsible for transporting the largest proportion of eroded soil.
- Deposition: When the wind’s velocity decreases, it loses its ability to carry soil particles, leading to deposition. This can occur in sheltered areas or where the wind speed drops significantly.
- Soil Characteristics: Soils with smaller particles (like sand and silt) are more prone to wind erosion because they can be easily detached and transported by wind. A smooth, bare soil surface, especially in the absence of vegetation, increases the susceptibility to wind erosion.
- Wind Velocity and Duration: Wind erosion occurs primarily when wind speeds are high. The greater the wind velocity and the longer it lasts, the more intense the erosion will be.
Control Measures for Wind Erosion
Several methods can be implemented to control and reduce wind erosion. These measures can be categorized into vegetative measures, tillage practices, and mechanical measures:
- Vegetative Measures
Vegetative cover plays a crucial role in reducing wind velocity near the soil surface, thus preventing soil detachment. Vegetation provides resistance to the wind, reducing its speed and trapping particles before they can be transported. There are two types of vegetative measures:
- Temporary Measures: These include the use of cover crops or crops grown specifically for soil protection. These crops are grown during the windy season to prevent soil erosion.
- Permanent Measures: Permanent vegetation like grass, shrubs, and trees can be planted to provide long-term protection. The use of windbreaks and shelter belts falls under permanent vegetative measures.
Examples:
- Windbreaks: A windbreak is a row of trees or shrubs planted to block the wind, reducing its velocity and preventing soil erosion. These barriers are most effective when planted perpendicular to the prevailing wind.
- Shelter Belts: Similar to windbreaks, shelter belts are longer barriers made up of multiple rows of trees and shrubs, designed to protect fields and crops from wind erosion.
- Tillage Practices
Proper tillage practices can help in controlling wind erosion by either roughening the soil surface or conserving moisture, making the soil less prone to being carried away by wind.
- Ploughing: Ploughing helps break up the soil and increases roughness, reducing wind speed near the surface. It also helps conserve moisture, which can bind soil particles together and make them less susceptible to erosion.
- Surface Roughening: Tillage practices such as disc ploughing can create ridges in the soil, which help trap soil particles and reduce the impact of wind. These practices are particularly useful when vegetation cover is insufficient.
- Strip Cropping: This practice involves planting crops in strips with alternating rows of crops and fallow land. This reduces wind velocity and provides windbreaks between the strips, minimizing soil movement.
- Mechanical Measures
Mechanical or structural measures involve the use of barriers or physical structures to reduce wind velocity and control soil movement.
- Windbreaks and Shelter Belts: These are physical structures, often combined with vegetation, that reduce the wind speed, thus limiting the potential for wind erosion.
- Stone Packing or Fences: In some areas, stone walls or fences can be constructed along the prevailing wind direction. These barriers reduce wind speed and prevent the movement of soil.
- Terraces and Bunds: Building terraces or bunds (embankments) along the slopes can also reduce wind velocity and control erosion, especially in areas prone to both wind and water erosion.
- Sand Dune Stabilization
In areas affected by sand dune formation, stabilization techniques are necessary to prevent further movement of sand. Some common methods include:
- Vegetative Stabilization: The use of plants to anchor the sand, particularly grasses or shrubs, helps stabilize dunes. These plants trap windblown sand and prevent it from shifting.
- Straw or Netting: In some areas, straw or other biodegradable materials are placed over dunes to hold them in place temporarily until vegetation can establish itself.
- Chemical Stabilization: In some cases, chemical agents like crude oils or synthetic polymers are sprayed over sand dunes to reduce their erodibility. However, this is a temporary solution and can be expensive.
