Erosion Essay

Soil Erosion Essay

Soil Erosion

Introduction

The term soil erosion generally means the destruction of soil by the action of wind and water. Some authors have modified this definition to include damage that is caused as a result of human actions. (D. Zachar p. 22)

Soil erosion causes a lot of damage. Apart from environmental damage involved, the financial losses associated with soil erosion are immense. For instance, America loses between $30 billion and $44 billion to soil erosion annually (Pimental et al 1993), whereas The United Kingdom also loses about £90 million (Environment Agency 1989).

The purpose of this study is to examine the causes of soil erosion, its effects on the environment and the solutions available to control it, for the purpose of academic study.

The Causes of Soil Erosion

Soil erosion is mostly caused by climatic factors. They include rainfall and wind as the major factors. Other factors that contribute to soil erosion are mostly caused by human activities. Such activities include mining, urbanization and vegetative clearing. The topography of the land also contributes to soil erosion.

Rainfall intensity contributes greatly to soil erosion. It is usually the main agent of erosion. The amount of intensity influences the magnitude of the erosion. It is the most critical factor. The greater the intensity of the rainstorm, the greater the runoff and consequently, soil erosion. (Blanco, Lal p 29).

Vegetative clearing is another factor that contributes to soil erosion. It is estimated that about 1 million hectares were cleared from the year 2000 to 2010. (SOE 2011 Report). Vegetation has a great role in preventing soil erosion. It reduces the destructive energy of rain by increasing the soil roughness. This is effective in slowing the runoff velocity. The vegetation also filters the soil particles in the runoff thus preventing further erosion. With less vegetation, the detachment of soil particles increases thus making the soil prone to erosion. Although vegetation is crucial in providing cover and averting erosion, not all vegetation play this role effectively. Dense and short growing form of vegetation, for instance, grass, is preferable to sparse and tall vegetation. Dense canopies also limit splash erosion therefore reducing soil erosion. . (Blanco, Lal p 29).

Population pressure greatly contributes to soil erosion. In China, for example an exponential rise in erosion with a rise in the total population was recorded since 220 BC (Wen, 1993). When the population is large, land becomes scarce, forcing people to farm on marginal land. The farming practices carried out on these lands are usually unwise and therefore lead to soil erosion (R. P. C. Morgan). For example, people often farm in mountainous regions such as The Himalayas in China thus exposing the soils to soil erosion. Rural to urban migration...

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Soil is one of the most important natural resources of man. Soils are essential for man for growing crops, fodder and limber. Once the fertile portion of the earth's surface is lost, it is very difficult to replace it. In India, the destruction of the top-soil has already reached an alarming proportion.

Land degradation problems have resulted in increasing depletion of the productivity of the basic land stock through nutrient deficiencies. In addition to the direct loss of crop producing capacity, soil erosion increases the destructiveness of floods and decreases the storage capacity of water in reservoirs.

It is therefore essential that the soils should not be allowed to wash or blow-away more rapidly than they can be regenerated, their fertility should not be exhausted and their physical structure should remain suited to continued production of desired plant materials.

Protection of land from further degradation, adoption of various conservation measures, including reclamation and scientific manage­ment of available land stock is very important for a country like India to achieve higher productivity of food, fodder, fuel and industrial raw materials on a substantial basis.

Besides, demand for land for providing social priorities such as shelter, roads, industrial activities is increasing at a very fast rate with the rise in population and very often good agricultural and forest lands are being diverted to such use.

It is, therefore, necessary to keep soil in place and in a state favourable to its highest productive capacity.

Soil Erosion

The process of destruction of soil and the removal of the destroyed soil material constitute soil erosion. According to Dr. Bennett "the vastly accelerated process of soil removal brought about by the human interference, with the normal disequilibrium between soil building and soil removal is designated as soil erosion".

Types of Soil-Erosion

Erosion of soil by water is quite significant and takes place chiefly in two ways (a) Sheet erosion, (b) Gully erosion.

(a) Sheet movement of water causes sheet erosion and depends on the velocity and quantity of pronounced surface runoff and the erodability of the soil itself. In such cases, the soil is eroded as layers from the hill slopes, sometimes slowly and in­sidiously and sometimes more rapidly. Sheet erosion is more or less universal on:-

- all bare follow land,

- all uncultivated land whose plant cover has been thinned out by over grazing, fire or other misuse, and

-all sloping cultivated fields and on sloping forest, scrub jungles where natural porosity of soil has been removed by heavy grazing, felling of trees or burning etc.

The particles loosened and shifted by the rain drops are carried down slope by a very thin sheet of water which moves along the surface. The impacts of the raindrops increases the turbulance and transporting capacity of this unchannelized sheetwash which results in the uniform skimming of the top soil.

Sheet erosion is considered as dangerous as it may continue for years but may or may not leave any trace of the damage. Sheet erosion is common in the Himalayan foot­hills, in Assam, Western ghats and Eastern ghats.

When sheet erosion continues unchecked, the silt laden run-off forms well-defined minute finger shaped grooves over the entire field. Such thin channeling is known as 'rill-erosion', which is active over wide areas in Bihar, Uttar Pradesh, Madhva Pradesh and in semiarid areas of Maharashtra, Karnataka, Andhra Pradesh and Tamil Nadu.

(b) Gully erosion

On a gentle slope, adequately covered by vege­tation, clay soil will resist erosion to a great extent and the water forms small rivulets which can then erode deeper. The rivulets in turn join together to form larger channels until gullies are formed gradually deep gullies cut into the soil and then spread and grow until all the soil is removal from the sloping ground.

This phenomenon once started and if not checked, goes on extending and ultimately the whole land is converted into a bad-land topography. Gully erosion is more common in areas where the river system has cut down into elevated plateaus so that feeders and branches carve out an intricate pattern of gullies.

Apart from this, it also takes place in relatively level country whenever large blocks of cultivation give rise to con­centration of field run-off.

Wind Erosion

It occurs in dry climatic areas having a sparse and low vegetation cover on mechanically weathered, loosened surficial material. Dust storms are the principal agents of wind erosion.

The top soil is often blown off from the surface rendering it infertile. Besides, with the decrease in the wind velocity coarse sand particles get deposited in some areas covering the existing soil and rendering it unproductive.


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