Soil erosion in Assam
25th Dec, 2010
Erosion is a comprehensive natural process of detachment and removal of loosened rock materials and soils by exogenetic processes such as running water, ground water, sea waves, wind, glacier etc. there are two types of erosion:
Ø Geological erosion and
Ø Accelerated erosion.
Erosion caused by natural processes without being interfered by human activities is called geological erosion. Accelerated erosion refers to the increased rate of erosion cause by various land use changes effect by man.
Soil erosion is one type of accelerated erosion, which is also called as Man-Included Erosion because of greater impact of human activities than natural factors of soil erosion. Soil erosion involves mainly two processes:
Ø Loosening and detachment of soil particles from the soil mass.
Ø Removal and transport of the detached soil particles down slope, down stream or down wind.
Soil erosion is a common characteristic of the fields of Assam. The highly productive and fertile soils of Assam are now facing the serious problem of soil erosion like other parts of the country. Riverbank erosion during high flood period in the valley is a regular annual feature. The extent of loss to the bank erosion varies from year to year depending on the severity of floods in the state. Thousands of Mising tribe is under threat due to heavy soil erosion in Assam's Sumoi Mari village. The Bramhaputra River floods the village situated in Majuli quite often, causing immense erosion of fertile and cultivatable land. Over bank flood due to breaches in the embankment, render the fertile cultivable land unsuitable for crop production due to deposition of coarse sand on the surface to a variable depth.
Various surveys carried out by the Soil Conservation Department of Assam Government have indicated towards the fact that Jhum cultivation is the major reason for such widespread soil erosion in the state. As per Assam Government Revenue Dept. records, an area of 6116 hectares of land was affected by soil erosion in Upper Brahmaputra Valley and North Bank Plain zone during 1994.
In Assam the most common type of soil erosion is loss of topsoil through surface run-off under heavy precipitation and humid climate. Nearly 3.2 million hectares of land of the plain districts of the state are vulnerable to topsoil erosion with varying intensity.
Terrain deformation through mass movement is another type of soil degradation, which is primarily confined to the hill districts of Karbi Anglong and N.C. Hills covering an area of about 1.53 million hectares. Another important type of soil erosion in the state, which assumed serious proportion in the recent time, is the bank erosion by the rivers.
Table: Soil Erosion Statistics of Assam:
|a) Total Cultivable area in Assam||34,60,082 ha|
|b) Area affected by Soil Erosion||1,93,000 ha|
|c) Area under Wasteland & Degraded Land||2,71,556 ha|
|d) Area affected by shifting cultivation||1,70,000 ha|
|e) Average area being eroded due to flood and soil erosion problems||6,500 ha|
|f) Average area affected by Flood annually||4,50,000 ha|
|g) Average annual rainfall in Assam||2,4000 mm|
Total Annual Silt Load of Brahmaputra (1990)
Soil Erosion rate (1990)
Jia Bharali River
4,721 Tonnes per Sq.Km
2,887 Tonnes per Sq.Km
(Source Directorate of Soil Conservation Ulubari, Guwahati-7)