FLOOD MANAGEMENT IN SUB-HIMALAYAN RIVERS

Econirvan-Bihar's Revival.

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ADDRESSING KOSI

Posted by gajananmishra on October 23, 2012 at 11:00 PM

The Kosi is “Disaster in Waiting” because of its sedimentation within the embankments. Otherwise also, it is a problem because of its vicious FLOODING and SHIFTING channel. The Suggestions by RAI BAHADUR PRAFULLA CHANDRA GHOSH seem to be well addressing the problems.

P. C. Ghosh( executive engineer, PWD, Bihar in 1941) suggests:

“the main problem in training the Kosi is its high discharge, high velocity and the vast amount of boulders, pebbles, silt etc. which it brings down. Of the above three factors, the last one is the most important. The whole safety of any project for training of the Kosi would lie in the scientific disposal of the high percentage of silt which the Kosi carries. The easterly and the westerly peregrination of the Kosi which is the most dreadful feature in the destruction of the area is solely due to the raising up the country level of the area over which She flows by yearly deposit of silt and finally adopting another channel in the west after raising the bed of its own channel.’

‘To regulate the percentage of the Kosi silt would be entirely difficult. It can be done partly by stopping Deforestation and Surface soil Erosion due to cattle grazing in the hill area where from the silt is gathered by the river. Also the high velocity of the Kosi in the Sub-mountainous region has got a wearing action on the soft sand stone. This accumulation of sand by the Kosi water can only be checked if the velocity can be reduced to a safer limit so that the wearing action may be lessened.’

‘ Reduction of velocity may be done by constructing a number of Weirs across the tributaries of the Kosi above the Varahkshetra in their mountainous region. Such weirs may also help in reducing the flood height in British India as the Reservoirs so formed will act as retarding basins at the time of floods. The catchment area of such retarding basin can well be expected to be pretty large. Detailed survey of these valleys is recommended to be made in order to know the feasibility of such a scheme.’

‘Also the flood disaster due to the Kosi may be reduced by redistributing the Kosi discharge into Two channels, viz. the Kosi and the Sursar at Chatra by erecting extensive Barrage works at the point of bifurcation. The discharges thus brought down by the Sursar and the main Kosi channel further lower down may be distributed into various dead channels by making Diaphragms at their off-takes.’

‘If in this way the amount of flood water be controlled according to the capacity of the channels( which nay have to be kept of proper section by constant dredging operation) the area over which such channels flow would be built up uniformly and thus there will be lesser chance of the Kosi, shifting from one to the other.”

(A Comprehensive Treatise on north Bihar flood problem…..page no. 120.)

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