Thursday, September 11, 2008

Kosi floods in Bihar, India- Different methods to minimize flood must be adopted.

Kosi floods in Bihar, India- Different methods to minimize flood must be adopted.
By

Dr. Nitish Priyadarshi

Seeing devastating floods by the kosi river now it is ripe time to search for the methods which can help to minimize such floods. Earlier I have suggested for the construction for new big dams in the Bihar state on kosi river. There are other methods too which can be implemented in the affected areas. Most important is removing the sediments from the river beds because every year Kosi contributes heavy sediment in Bihar plains. Owing to extensive soil erosion and landslides in its upper catchment by factors both natural and human, the silt yield of the Kosi is about 10 cubic yard /acre/yr, one of the highest in the world. It was observed earlier that at many locations water level in the channel within the embankments is significantly higher than the general ground level in the surrounding areas. Deposition of sediments either within the channels or on the channel margin restricts the passage of water and thus reduces the carrying capacity of the channel.
Making inter-linking canals parallel or vertical to the flow of the river can also be adopted, so that surplus water during the rainy season can be diverted to other areas devoid of water. Small check dams should be built in frequent intervals in the canals to maintain water level. Building canals is not the recent method. The oldest known canals were built in Mesopotamia circa 4000 BC, in what is now modern day Iraq and Syria. The Indus Valley Civilization in Pakistan and North India (from circa 2600 BC) had a sophisticated canal irrigation system. Agriculture was practised on a large scale, and an extensive network of canals was used for the purpose of irrigation. Sophisticated irrigation and storage systems were developed, including the reservoirs built at Girnar in 3000 BC.
Construction of storage dams along the river course will considerably reduce the severity of floods and the resultant damages.
Interlinking of kosi river with other rivers is expected to greatly reduce the regional imbalance in the availability of water. Surplus water which spreads in bigger areas during floods would be fruitfully utilized.
Flow diversion is one of the efficient ways of coping with flood situation. The primitive way of achieving this is to break levees in the area where the flood damage will be relatively small. Such area should be a depression surrounded by secondary dikes, and free of habitation. Further, there should be good drainage facilities to get the water back into the river after the flood recedes. Diversion channel is an effective way of diverting part of the flow.
Water management is perhaps the most serious problem facing the nation. The critical problem is the uneven distribution of the run-offs and precipitation rates during the monsoon season. In the kosi and Ganga regions not only is the area liable to floods high, but the frequency at which the floods occur is also high. In general human life in the Kosi and Ganga plains is significantly affected by the flood hazards more often than in the Peninsular India, where the areal extent of the flood-prone lands is limited and the recurrence interval of big floods is greater.
Large floods on most of the North Bihar rivers are a direct result of intense cyclonic storms and depressions. Also due to effect of global warming, glaciers in the Himalayas are melting which are contributing water to the rivers. Water from the melting glaciers and rain water together is creating menace over the area.
Some of the largest and most calamitous floods in the Indian subcontinent have been produced from failure or breaching of natural or man-made dams as it happened in Kosi dam built in Nepal. Seeing this situation I earlier suggested for new big dam on the Kosi river in Bihar. Building big dams will definitely create problems like displacement, more area coming under water etc. But seeing the miseries, deaths and displacements due to devastating floods on large scale every year by the people of North Bihar ,one time displacement can be accepted.
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