Normal And Man Made Erosion
Weathering of parent rock and erosion are natural processes by agencies like water and wind. This type of erosion occurring in nature is normal or geological erosion. If both the processes are equal i.e., erosion removing as much top soil as the weatchring processes from it, there is not much harm done, but it is generally not so. In order to provide food and shelter, man has cut down forests indiscriminately, allowed grazing of grasses excessively and ploughed the land and exposed it to nature with the result that erosion of soil has been faster than it was formed.
This is man – made erosion and is a result of bad land management. The worst form of cultivation is shifting cultivation. The practice is common with tribal communtics. They fell the forest and burn all vegetation and cultivate the cleared areas for 2 to 3 years and then abandon them for some years. This accelerates erosion and many good hill slopes have been denuded of vegetation and top soil, making tem barren.
Damage Caused By Erosion
Erosion does not only cause considerable damage to good fertile and but is also detrimental in many other ways which are discussed below:
1. Washing away of fine soil: The top 18 cm. of soil is most important from the point of plant growth. Eighty p.c. roots of the plants are found in the surface soil and they absorb their nutrition and water from that zone. If the top soil is washed away by erosion, the water holding capacity of the soil is decreased and productivity goes down.
2. Deposition of coarse material in low lying areas: Low lying areas are exposed to the danger of deposition of coarser particles which are washed from higher hilly areas. This makes the soil less productive. It is also a common experience that during floods good fertile soils on the river banks are corded and covered with layers of sand with the result that they become infertile.
3. Silting of tanks: Tanks get filled every year during monsoon season by water from catchments area. This water also brings with it large quantities of silt and day. If proper antierosion measures are not taken in catchments area, reservoirs get silted and their storage capacity is considerably reduced.
4. Lowering of the underground water table: If surface run off is allowed to go on unchecked, the quantity of water that should infiltrate into the soil is very much decreased. Water table in wells goes down as underground water is not replenished and irrigation cost goes up.