Wind Erosion and Control Questions and Answers

Answer: B

The maximum portion is transported by saltation.

In wind erosion, particles of medium size, roughly 0.1 to 0.5 mm, are lifted briefly into the air and fall back in short bouncing hops, striking and dislodging other particles. This saltation carries the largest share of the eroded soil, usually put at about 50 to 75% of the total.

Suspension moves the finest particles high and far, but they form a smaller fraction of the moving soil. Surface creep rolls and pushes the coarser particles along the ground, set moving by the impact of saltating grains. Bed load is a term for sediment moved along a stream bed by water, not by wind.

Answer: D

The soil transported varies directly as the cube of the difference between the actual and threshold wind velocities and as the square root of the mean soil particle diameter.

Soil is moved only when the wind exceeds the threshold velocity at which particles start to roll and saltate, so it is the excess velocity \((V - V_{t})\) that drives transport. The relation used in soil conservation texts follows Bagnold's work on blown sand: the rate of soil movement grows with the cube of that excess and with the square root of the mean particle diameter, \(q \propto (V - V_{t})^{3}\sqrt{d}\).

The options using the threshold velocity alone or the actual velocity alone miss the fact that only the excess over the threshold does work, and they also wrongly make transport fall with particle size squared. The option with the square of the diameter has the right velocity term but the wrong power of \(d\).

Answer: C

Wind erosion is common in arid and semi-arid regions.

Wind erodes soil where the soil is dry, loose and finely divided, the surface has little vegetation, and winds are strong. These conditions occur together in regions of low rainfall: the deserts and semi-deserts. In India, western Rajasthan and parts of Gujarat and Haryana are the main areas.

Humid regions have moist soil and good plant cover, which hold soil against wind; erosion there is mainly by water. 'Arid region' alone is not wrong, but it leaves out the semi-arid regions, which also suffer badly, so the fuller option is the answer.

Answer: A

The short bouncing movement is saltation.

Wind moves soil in three ways. In saltation, particles of about 0.1 to 0.5 mm are lifted, carried a short distance and dropped, bouncing along the surface; it carries the major part of the soil moved, often 50 to 75%. In suspension, very fine particles are carried high and far by turbulence. In surface creep, larger particles roll and slide along the ground, pushed by the impact of saltating grains.

So suspension and surface creep are real modes but carry less soil and do not involve short bounces.

Answer: D

The condition that does not favour wind erosion is Presence of moisture in the soil.

Moist soil particles cling together through the cohesion of water films, so wind cannot easily detach and lift them. Wind erosion therefore occurs mainly when the soil surface is dry, loose and finely divided.

The other three all favour wind erosion: a dry period leaves the surface dry and loose; broad, flat or gently undulating land lets wind blow unchecked over long distances; and bare ground without plant cover or residue gives the wind direct access to the soil.

Answer: B

The factor with minimum influence is Fauna.

Wind erosion at a place is governed mainly by climate (wind velocity, rainfall and soil moisture), by the soil itself (texture, structure, aggregate stability, surface roughness) and by vegetation, which shields the surface and slows the wind near the ground. These are the factors in the standard wind erosion equations.

Animals affect wind erosion only indirectly, for example when overgrazing removes plant cover; their own influence is small compared with the other three, which is why fauna is the answer.