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EROSION- CAUSES AND CONTROL

The surface of the earth/land suffer from various types of erosion or degradation.Erosion is pronounced particularly where the man has interfered with the

ecological balance by reshaping or defacing the topography.

PROCESSES OF EROSION:

Water Erosion:

In the absence of the vegetal cover, rainfall initiates a set of processes viz., rain

splash erosion, sheet erosion and gully erosion.The processes are accelerated

more if the topography is steeply sloping, the soil has been loosened by activities

of humans, and precipitation is heavy and prolonged. The falling rain-drops

possess considerable energy and loosen the soil and initiate erosion by dispersing

its aggregates and splashing them around. In the absence of intercepting trees,

shrubs and grasses, the raindrop erosion (rain splash assumes serious proportions

as billions of drops pound the soil surface and splash the particles downslope. This

type of erosion is more common in the fields without crops, in clear felled forests,

on road cuttings, and na!ed slopes etc. "hen the rainfall is very heavy or when

the soil has lost its capacity to absorb the water, the rainwater accumulates on the

ground and flows down slope in the sheet manner. The intensity of sheet erosion

depends on the steepness of the slope and on the volume of water flowing. #uring

the flow the water may get separated in to threads of water flows giving rise to

gullies, giving rise to gully erosion. If such gully erosion are vigorous they giverise to gorges and canyons.

In the unconsolidated soil, the rain water infiltrates easily and washes the finer

clay or silt particles. $uch continuous interstitial flows give rise to the widening of

crac!s, or

develop networ! of tunnels. The resultant features are more common in carbonate

roc!s !nown as !arst topography. The collapse of the underground tunnels, caves

or cavities give rise to swallow holes. The intensity of erosion depends on both

volume and velocity of water.

Wind erosion in dry lands:

"ind erosion involves winnowing/deflation or carrying away of finer particles of

soils (%&.' mm and abrasion of coarser particles. This again is dependent upon

the wind velocity, the cohesion of the soil/sediments and the moisture in the soil.

The sediments/soil particles are carried long distances and are deposited wherever

the wind velocity is chec!ed to form dunes and then deserts.

Coastal Erosion:

The sea coasts are endlessly and heavily affected by wave and current action. The

erosion is prominent during the monsoons, storms and cyclones, which possess

enormous energy. The erosion of headlands and cliffs along the coast are affected

due to the wave action and longshore currents formed due to the obliue approach

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of the waves to the coast, and due to wave refraction. )oastal erosion is severe

near the estuaries or river mouths in the down drift sides.

CAUSES OF ACCELERATED EROSION

*ass movements li!e the slow downslope movement of soil material (creep and

the rapid slide of debris and roc!masses (landslide cause destruction of the slope

and ground surface, initiating a chain of uncontrolled erosion in the mountain

terrain. +eavy rainfall or cloudbursts and rapid melting of snow in higher altitudes

contribute considerably to destabilization of the slopes. Ecavations for mining,

roads, canals, buildings, etc., have added greatly to the mass movements and

intensification of erosion in the hilly terrain.

Overgraing in Forested Area:

The pounding and trodding by hoofs of grazing animals not only destroy the

vegetal carpet but disaggregate the soil mantle also. )attle trac!s later grow intogullies. The greater the grazing, the more intense would be the erosion.

De!orestation:

The erosion due to deforestation is chiefly due to three causes- destruction of

foliage that intercepts raindrops,decay of roots that hold together and stabilize the

soil on roc!y foundations, and deprivation of humus that binds together soil

aggregates. It is thus clear that the vegetal cover in the forests provide very

effective protection to the ground and prevent more than a third of the total

rainfall from reaching the ground. +ence the larger the canopy the better would be

the protection.

Uns"ienti!i" Agri"#lt#ral Pra"ti"es:

If the rows of grooves made by ploughing on agricultural lands are not !ept

parallel to the contour of the hillslope, they become channels for rainwater. The

furrows become gullies, and the gullies enlarge to become streams and rivulets.

#uring heavy rainfall the furrows deepen and widen, and a networ! of gullies

develop eventually giving rise to badlands. The longer the rains, and less protected

with vegetation a field is, the greater would be the erosion.

Road Constr#"tion:

The amount of sediments eroded away is more at the sites of road construction

compared to the cultivated lands. #uring the construction of the roads, thestability of the hill slopes is disturbed, hydrologic system is damaged and the

protective vegetal cover is removed.

$igration o! Strea% C&annels in Flood Plains:

"hen a river is in flood, it often changes its course or gradually migrates by

cutting its ban!. Ecess sediment load causing silting up of channels forces the

river to spread and

erode its ban!s.

I$PACTS OF EROSION:

The damages by erosion are serious at our agricultural fields, hence conservationmeasures are needed for soil erosion. The land is eroding at an alarming rate.

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Erosion is not noticeable within a shorter span of time, i.e. not until the ground is

eroded to the depth of the bedroc! or infertile subsoil, which may ta!e several

years. The net maor impact of the land erosion is the passage of great volumes

of sediments through the channels or rivers and streams. ot all the sediments

eroded is carried away to the oceans, rather uite a part of the sediment is

deposited in the channels and on the floodplains. *aority of this deposits are nonfertile, effecting adversely the productiv-

ity of the farms on the floodplains. The shallowing channels ma!e the rivers

difficult for navigation and the siltation of these rivers effect on the potential

generation of electricity and water recharge.

RE$EDIAL $EASURES

Waters&ed treat%ent 0eduction of loss of soil can best be achieved by covering

the watershed with vegetation- multistratal forests with trees, shrubs and grasses.

The threatened or erosion prone area is first put under cover of uic! growing

plant spe-

cies and then deeproot long maturing trees to restore the original condition. The

conservation measure in the ravineland involves plugging the gullies by

constructing a series of chec! dams at intervals of one to two metres then leveling

the ground with bulldozers, and finally covering it with grass.

Prote"tion o! Agri"#lt#ral Fields In addition to contour terraces in the field,

contour wattling would considerably strengthen the stability of the ground.

0otation of crops, minimum tillage, strip cropping etc., would prove beneficial in

controlling the soil erosion.

Controlling Landslides The routine measures of building retaining walls, etcare uite effective in case of minor hazards.

Strea%'an( sta'iliation )hannel beds and sides can be protected by

introducing vegetation-trees and bushes on levees or emban!ments. These are to

be generally planted during the rainy season. In order to !eep erosion at a minimal

level, the channel grade is made flat by inserting massive intervention such as

dams and bunds. The energy of water is reduced by ma!ing basins, or ma!ing the

beds irregular by putting a series of drop structures with adeuate spillways.

Saving "oasts There are three ways to protect coasts from erosion by waves,

currents and tides. 1ffshore brea!waters intercept waves and provide protection.

The seawalls and bul!heads are located on or near the upper beach and seawardface of the beach scarps. 2roynes have proved successful in arresting erosion by

building beaches in a maority of cases. These are linear structures built in groups

and placed perpendicular to the coastline at intervals. 3etties are massive

structures, generally in pairs, constructed along the channels of estuaries and

lagoons and in harbors. They chec! littoral transportation of beach sediments,

resulting in updrift development of the beach, but downdrift erosion.

Co%'ating Wind erosion

4ences of trees and shrubs and windbrea!s help to chec! the advance of sands.

5pplication of chemicals, asphalt and rubber solutions stabilize the surface of the

dunes. "indbrea!s consist of several rows of trees and/or shrubs placed at rightangles to the direction of the wind. 6lants are grown close enough to provide a

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continuous barrier against the wind. 1n the windward side, shrubs and short trees,

in the middle fastgrowing shortlived trees and in the leeward side tall and

longliving trees are planted.