Tista Flood Problem in West Bengal — Embankments No Solution

May 19, 1956 Tista Flood Problem In West Bengal — Embankments No Solution Kumud Bhushan Ray AT a meeting at Darjeeling on due to erosion of river banks, there became homeless and damage to April 4, 1956, the Technical Com is gradual decrease in the velocity property was estimated at 270 mil mittee of the State Flood Control of a current of water. The drainage lion dollars. Hence after the floods Board, West Bengal, proposed that capacity of a river also decreases. of 1927, instead of raising levee an embankment should be construct With inadequate drainage capacity, heights, three overbank leveed flood- ed at a cost of Rs. 20 lakhs on the excess water goes into channel stor ways have been constructed to drain left bank of the Tista River for pro age, so that the flood water level away the surplus flood water that tection from floods in the Barnes- in the river goes on rising. When cannot be accommodated within the Mainaguri area. Now an embank the water level rises to the brim of leveed river channel. ment along the right bank of the the channel, excess water goes into In the U S A, levees have also Tista River was constructed in 1955 valley storage, riverside lands are been found to accentuate the mean for the protection of Jalpaiguri submerged and there are floods. dering tendency of a river. The Town (AB, see Fig. 1). After the River water transports silt load. Yazoo Levee District in the Lower proposed left embankment is con The catchment of the Tista lies in Mississippi River has 178 miles of structed, the flood waters of the the Himalayas, which are 'young' levees. Owing to erosion of river Tista in the Jalpaiguri-Barnes-Mai- mountains formed in the tertiary banks and consequent meanderings naguri area will be confined within era of geological time. An enormous of the channel, the original levees its wide channel. The question that amount of detritus is formed by the have mostly been undermined and naturally arises is: will this pair of action of nature's forces of denu destroyed, necessitating the construc embankments provide a permanent dation, which forms the silt load of tion of new levees on successive solution to the Hood problem posed the waters of the Tista. The power retired alignments. A total of 305 by the Tista? of a current of water to transport miles of levees has therefore had to a silt load varies in geometrical pro be constructed for the maintenance Embankments constitute the old gression with its velocity. Hence of the original 178 miles of levees in est form of river engineering in the as the velocity of a current the Yazoo Levee District. alluvial plains of the world. In of water decreases, it goes on de In India also embankments or as China they have been in use since positing a part of its silt load on 603 B C having been first construct they are called 'bandhs' have been the channel bed, raising its level. found to give rise to more evils than ed in different provinces in the in With a rise in the level of the chan terests of Individual land-owners. they eradicate. In his book, 'Vari nel bed. there is automatically a ous Problems connected with the In A D 69 under the Han Dynasty rise in the flood water level also. they were also put up along the Maintenance of Rivers and Drain- banks of the Yellow River, but old Thus the construction of em age Systems of the Gangetie Delta', records show that serious difficulties bankments along a river causes a (1920, Addams-Williams. a Chief were experienced after their con gradual rise in flood water levels in Engineer of Bengal, wrote: struction: in many instances they its channel, and in a few years, the "With regard to embankments, proved uneconomical and sometimes height of the embankments becomes our experience has been that positively harmful. insufficient. To keep the flood water wherever they exist, they have confined within the embankments, it Embankments do not prevent raised problems as great as, if becomes necessary to raise their erosion of river banks, so that the not greater than, those with which height. In China, as a result of channel gradually becomes wider they were intended to deal; either repeated raising of the height of em and shallower and develops a tortu in course of time they have raised bankments, the Yellow River now ous alignment. The hydraulic mean flood levels, or have led to the ex flows high on a ridge of its alluvial depth of a wide and shallow channel tinction of rivers by causing silt plain. i is less than that of a narrow and ing, and have brought about water deep channel of the same sectional In the U S A., embankments or logging and severe epidemics of area, so that when owing to erosion levees were constructed along the malaria and other diseases". Mississippi River near New Orleans of river banks there is widening and In his Foreword to the Book, A in 1777. Between the years 1833 and shallowing of a channel, its hydrau Comprehensive Treatise on North 1927. the heights of levees were lic mean depth goes on decreasing. Bihar Flood Problems by Ghosh, raised by as much as 17 feet, be Moreover with the development of a Hall, a Chief Engineer of Bihar, too tween Memphis. Tennessee. and tortuous alignment, the length of came to the same conclusion: a river channel goes on increasing, Helena, Arkinsas. In spite of such so that its slope of water surface a rise, levels were overtopped and "In the old days, whenever a goes on flattening. The velocity of breached. In the year 1882, there flood problem arose, the answer a current of water in a river decre were 284 levee breaches. The largest was let us build a 'bandh Famine ases with a decrease in the hydrau number of levee breaches, however, relief work, which frequently com lic mean depth and also with a flat occurred during the great floods of prised the erection of bandhs, was tening of the slope of water sur 1927, in which 20,000 square miles in no small measure responsible face. Thus with the widening of a in 6 States were submerged; there for the present trouble. The pro channel and the formation of bends were about 350 deaths, 60,000 people blem is not to prevent floods, 080 May 19 1956 which has been the erroneous idea 3, Discharge Qs passing through the dry season low water level and in the past and which has led to a breach in the Barnes-Domohini in the flood season high water level the promiscuous construction of railway embankment. Section of From the gauge readings, maintain private bandhs which are the pri water flow through the breach ed at Barnes, the lowest water level mary cause 01 the havoc now 3500' x 5 Average velocity of registered in the dry season and the caused by floods, but to give them water about 8 feet per second Q., highest water level in the flood sea floods) an easy run-off." - 3500 x 5 x 8 140,000 cusecs. son in the years 1941-1954 are as In the publication, 'Multi-purpose, Total discharge carried by the shown in the table below. Projects in India: Damodar Valley.' Tista: A study of the gauge readings published by the Government of Q I:T Q, i Q, J Q, shows that there has been more or India , it is stated: 11,250 | 284.000 4 140,00 less gradual rise in the low water "The present policy of keeping cusecs. level from 258.84 in 1941 to 263.90 floods in check by marginal em 435,250 cubic feet per second cusees')in. 1954, or a total rise of about 5 bankments is not successful. It feet. Similarly there has been a costs large sums of money, is un- It will be seen that the 2 mile gradual fluctuating rise in the H-F.I. remunerative and does not pro wide Tista channel could carry a dis from 266.54 in 1941 to 277.50 in 1954, vide protection against major charge of only 284,000 cusecs, while or a total rise of over 10 feet. In floods. the amount of water spilling over this period, there has thus been an appreciable rise in the channel bed Experience in ancient China, in its left bank and flowing into the Dharla river was about 50 per cent and water levels in the Tista River the U.S.A. and in India, therefore near Jalpaiguri Town. makes it apparent that, embank of this. There is thus sufficient fall ments on a river provide no perma from the Tista into the Dharla to In the tributaries of the Tista, nent solution to the flood problem. induce such a large flow. The velo there has also been an appreciable city decreased, so that large volumes rise in the channel bed and water The Tista Channel of sand have been deposited on fer levels. For instance, in the Karala At the Ferry Crossing, connecting tile paddy lands. River, which has its outfall into the Jalpaiguri Town with Barnes across With a sectional area of the main Tista in Jalpaiguri Town, the dry the Tista, the channel width on Tista channel at 35.500 square feet, season water level on March 16, 1955, March 13, 195,5, way 11,510 feet or a and width of channel at 11.540 feet, just south of the bridge on the Rail little over 2 miles, while the low the average depth of water in the way Station Road, was 4' 6" above water level in the flowing channel channel is about 3 feet.

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