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 favorable 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 Dry.
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 readability 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 turbulence and transporting capacity of this uncivilized swathes which results in the uniform skimming Of the top
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 Briar, Attar Pradesh, Madhya Pradesh and in semiarid areas of Maharajah’s, Karakas, Andorra Pradesh and Tamil Nadia.
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 surgical 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 mom areas covering the existing soil and rendering it unproductive. The removal of soil by running water and wind is known as soil erosion. The soil-forming process and the erosion process of running water and wind are continuous. Generally, there is a balance between these two processes. The rate of removal of fine particles from the surface is the same as the rate of addition of particles to the soil layer. Sometimes such a balance is disturbed by natural or human factors, leading to a greater rate of removal of soil.
When this happens, the entire soil layer may be removed in a few years. Types of Soil Erosion: Wind and water are powerful agents Of soil erosion because Of their ability to remove soil and transport it. (a) Erosion by Water: Erosion by water can be of several types, for example, sheet erosion, gully erosion, stream bank erosion, shore erosion and slip erosion. 1 . Sheet Erosion: When a layer of the soil on the surface is removed over a large area by running water, it is called sheet erosion. Sheet erosion is harmful since it removes the finer and more fertile top soil. 2.
Rill Erosion: This is the second stage of sheet erosion. Small finger-like rills begin to appear on the landscape. Over a period of time, the fine rills increase in number and also become deeper and wider. This reduces the actual area under cultivation and the yield of crops decline. 3. Gully Erosion: When soil is removed by Water flowing along definite paths downs the slope or in channels, it is called gully erosion. Gullies cut up agricultural land and make it unfit for cultivation. Badland is a region with a large number of deep gullies or ravines, e. G. , Cymbal Valley in Madhya Pradesh. 4.
Stream Bank Erosion: The continuously flowing water erodes the banks of streams and rivers. Gradually the bed of the river widens. 5. Shore Erosion: The tidal waves dash against coastal rocks, causing them to erode bit by bit. 6. Slip Erosion: During heavy rains, water percolates into the soil until it is unable to penetrate further by the underlying impervious rocks. On steep land, the heavy moisture-laden soil often comes down bodily, resulting in a landslide. (b) Wind Erosion is significant in desert and semi-desert regions. In regions with heavy rainfall and steep slopes, erosion by running water is more significant.
In some regions, the top soil is blown away by Wind in the dry season, and cashed away by running water in the wet season. Causes of Soil Erosion in India: Soil erosion takes place when soil is removed faster than it is formed. There are many different processes by which soil is removed but the cause is usually the removal of trees and other vegetation that hold the soil together and in place. 1. Topography and Slope of the Land: Hilly Region: Rainfall occurs in torrents and washes away the top layer of the soil. Also, the steep slopes stimulate the eroding power of the rainwater.
Plains: Here the erosion is comparatively less than on slopes. But in regions where the rivers overflow onto the plains, the erosion is severe. For example, the entire basin of the Koki River is threatened by the over-flowing of river. 2. Nature of Rainfall: Floods and torrential rains cause more damage than light or moderate showers spread over many days. I. The action of heavy rain is stronger when there are no trees and the plains are bare. Ii. When a prolonged dry spell is followed by sudden heavy rain, sheet erosion takes place. This is because the ground gets baked hard and the soil is unable to absorb the water easily.
Nature of Soil: Porous soils with good water-absorbing capacity are least subject to erosion, while the impervious soils are gradually eroded by the action Of water. 4. The Human Factor: Man and his activities are responsible for soil erosion to a great extent. As the human population increases, the demand on the land also increases. Forest and other natural vegetation are removed for human settlement, for cultivation, for grazing animals and for various other needs. Improper use of land leads to soil erosion. (a) Deforestation: is the removal of trees and other vegetation which hold the soil together.
When vegetation is removed, the soil surface is loose and more easily removed by running water and wind. Rain water that could have been absorbed by the soil, rapidly runs off the surface carrying soil with it. (b) Overgrazing of Land: by animals results in removal Of grass over a large area making it easy for wind and running water to remove the soil. In many parts of India, hill sides have become barren because of overgrazing by goats. (c) Improper Farming Techniques: Plunging fields in the traditional up and down manner along the slopes makes it easier for running water and wind to cause erosion.
Surface erosion When rain, wind or frost detach soil particles from the surface, the particles are washed or blown off the paddock. Sheet erosion This occurs when rain falls on bare or sparsely covered soil, loosening fine particles (silt, clay and humus) that are carried downhill in surface run-off. Sheet erosion lowers the fertility of the soil, because it removes the most productive layer, which has usually been enriched by fertilizer. Wind erosion The wind can remove the valuable fine soil on the land surface. Seasonally strong winds hit many areas, such as sand dunes, the Central Volcanic
Plateau, Wrapped, Hawker’s Bay, Canterbury and Togo. If covering vegetation has been grazed or disturbed, wind erosion can be severe. Fluvial erosion This occurs when running water gouges shallow channels or deep gullies into the soil. Rill erosion On sloping land, particularly if cultivated, water run-off may gather in small V- shaped channels or rills. These are particularly evident in pumice soils or those formed from loess (wind-blown dust), but can occur on all hill soils. Gully erosion Gully erosion occurs on unconsolidated subsoil. These are generally deep and generate a lot of sediment, which often feeds into rivers.
Gullies tend to erode at their head, eating back into the landscape. They are widespread throughout the country. In the sass, there was serious gully erosion in sandstone at Pinioning in the Manta;. Severe gulling also developed in pumice soils on the Volcanic Plateau when pastures were first sown. Tunnel GU Lying When water enters the soil on a slope, usually down cracks after a dry period, it scours out the subsoil to form a tunnel. The soil often later collapses inwards, and an open gully forms. Loess soils (fine dust) are very prone to this kind of erosion, especially on Banks Peninsula and in Marlborough.
Wither Hills near Blenheim had many severe tunnel gullies in the mid-sass. Once the surface was reshaped by bulldozers, some of this land has been used for growing grapes and olives. Although somewhat localized, tunnel gullies also occur in volcanic pumice and Northland weathered sandstones. Mass-movement erosion When gravity combines with heavy rain or earthquakes, whole slopes can slump, slip or slide. Muddy waters The Treadle slip is the largest in the southern hemisphere. It lies on the mudstone banks of the Wapato River, inland from Osborne, and adds a considerable amount of sediment to the river.
Forest has been planted on nearby former farmland to slow the growth of the slip. Slips Slips are one of the main forms of erosion in the North Island. They are a direct result of the change from forest to pasture. Slips occur when the soil (topsoil and subsoil) on slopes becomes saturated. Unless held by plant roots to the underlying surface, it slides downhill, exposing the underlying material. Slips are common where the underlying rock is mudstone (papa) or siltstone as in the hill country of Osborne, Taipei, Hanging, Tirana and King Country. The Wrapped hill country, where loess lies on north-facing slopes, s also susceptible.
In the South Island, soil slips are widespread throughout the hill country, but mostly north of Christopher. Awash with it During a February 2004 storm in Manta;, there were 62,000 landslides, totaling 1 ,OHO million tones of soil. About 50% came from hill-country farms. Flooding caused $1 00 million worth of damage. Around 210 million tones of soil are washed into New Zealand rivers annually: about 10 times the global average. This is a mix of natural and accelerated erosion. Earth flows These can be spectacular, but are not widespread. Saturated soils move onwards en masses, and may include underlying rock.
However, the surface vegetative mat stays intact, and forms humps and hollows. Screen erosion This occurs in steep or mountainous areas, where the underlying rocks are greywacke (in both the North and South islands) or schist (South Island). At high altitude, gravity pulls material downhill into a fan shape, which can be quite spectacular. There is debate over whether this is accelerated or normal erosion. What is clear is that scores can continue to move if vegetative cover is reduced, or stock track across their slopes. Streaming erosion This is common throughout New Zealand, especially in rivers and watercourses with periodic flooding.
Although not dramatic, it is significant because most of the valuable farmland lies beside main rivers, on alluvial terraces. Soil quality is one of the most basic and perhaps least understood indicators of land health. Soil supports plant growth and represents the living reservoir that buffers the flows of water, nutrients, and energy through an ecosystem. The ongoing degradation of the earth’s soils by human activity such as arbitration, deforestation, overgrazing of cattle, and poor agricultural raciest has brought about irreversible consequences that may lead to desertification of an area.