Environmental Science

92 ENVIRONMENTAL SCIENCE

Table 2.8 : Sediment load of some major rivers

(Brown and Wolf, 1984)

River Country Annual sediment load (Million metric tons)

Yellow China 1,600

Ganges India 1,455

Amazon Several 363

Mississippi USA 300

Irrawaddy Burma 299

Kosi India 172

Mekong Several 170

Nile Several 111

Table 2.9 : Estimates of excessive erosion of top soil from world cropland

(Brown and Wolf, 1984)

Country Total cropland Excessive loss

(Million acres) (Million tons)

USA 421 1700

USSR 620 2500

India 346 4700

China 245 4300

Total 1632 13200

Rest of World 1506 3138

Grand total 12200 25400

It is evident from the table that the loss of cropland soil is maximum in India as it is
18.5% of the total soil loss at global level. The situation is grave because India has only 2.4%
of the land area of the world. In USSR it is 9.80% whereas in USA only 6.70% (Fig. 2.6).

Kinds of Soil Erosion

There are various types of soil erosion. However, on the basis of the rate at which soil
loss takes place, there are two main types of soil erosion:

(1) Normal or geologic erosion

This type of soil erosion occurs under normal natural conditions by itself without any
interference of man. It is a very slow process, and equilibrium between loss and build up
is lost, only when there is some major disturbance by a foreign agent.

(2) Accelerated soil erosion

This type of removal of soil is very rapid and never keeps pace with the soil formation.
This is generally caused by an interference of an agency like man and other animals.