THE PROBLEM OF EROSION

 

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. 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. 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. It is observed that at some places, a few kilometers of bank along the villages, fertile agricultural lands and roads are being eroded by the rivers. Majuli, the largest river island of the world is now seriously affected by the erosion and virtually facing the threat to existence. The extent of loss to the bank erosion varies from year to year depending on the severity of floods in the state.

More than 4, 200 square kilometers of productive farm land in Assam were eroded in the last 40 years, about 0.9 million people, mainly poor smallholders and their families, lost their land and were left homeless and in poverty. By losing their land they also lost their social identity and backup within the rural community. Total economic losses, directly and indirectly caused by bank erosion, although difficult to quantify in their economic and social impacts in detail, were estimated in the range of billions of Euro.

The hydraulic river training measures are designed to protect against bank erosion and to concentrate river flow thus triggering the channelization of the river and deepening its bed. The latter process will establish a navigable river channel with sufficient depth to be used by cargo vessels with a capacity of up to 1800 metric tones. Shifting large quantities of transported loads from the road to the Brahmaputra River will considerably reduce the traffic pressure and maintenance demand of the road system. Consequently road maintenance will improve, and, eventually, significant funds will be released for supporting the river restoration activities.

 

The United Erosion Resistance Struggle Forum, a conglomerate of some 15 organisations, staged a sit-in demonstration in Jantar Mantar in New Delhi along with the Assamese students of Delhi on September 22nd 2010 to draw the attention of the Centre towards the alarming flood and erosion problem of Assam. The Forum submitted a memorandum to the President of India seeking her intervention for permanent solution to the alarming flood and erosion problem of the State.

 

Assam`s Water Resources Department has identified 25 vulnerable and very severe erosion-prone sites and estimated that the Assam valley portion of the Brahmaputra has lost approximately 7.4 percent of its land area due to river bank erosion and channel migration. Experts from Assam and the USA, who have formed a joint committee, christened the Committee for Developing Mitigation Strategies for Brahmaputra River. Basin flood and Erosion problems have come forward with a set of short and long term measures to address the problem and develop cost-effective solutions.

The experts have pointed out that the key factors in causing the river extremely unstable at many reaches are `aggradations` (raising of the river bed due to sediment deposition), intense `braiding` and large water discharge. They pointed out that till now both short and long term measures to tackle the erosion problem had been done only on a piecemeal basis during emergency situations depending on availability of funds. The experts have recommended phase-wise solution for the mitigation of erosion by including a combination of measures including strategic dredging, protection of erodible bank materials with anchored bulkhead or tie back sheet piles, spurs, toe and bank revetments.
Improvement of data quality and quantity by extending rain, flow and sediment monitoring network using state-of-the-art equipment and consider physical modeling to study severe and potential scour sites and their control have also been suggested by the experts.

The committee suggested strengthening and monitoring of anti-erosion measures already taken up at Majuli Island and severely eroded towns along the river and armouring existing embankments located at urban and other strategic locations.