May 19, 1956 Tista Flood Problem In West — 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, , 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 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 , 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 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. Thus, al­ the invert of the pakka drain out­ was 267.48. A remarkable feature though the river has a .steep slope fall, while previous to 1950 the dry was that from about 7.200 feet to of about 3.5 feet per mile near Jal­ season water level used to be 1' 6" 10,200 feet, the dry channel bed was paiguri Town, owing to the small below the invert. The rise in the in places as low as 262.71 (Fig. 2. average depth of water and conse­ dry season low water level in the This means that although a 3000 quent low hydraulic mean depth, the Karala Rivet' in the 5 years from foot width of the Tista channel was average velocity is only about 8 feet 1950 has. therefore, been 6 feet. lower than the low water level of per second. No wonder that with In the Ghish River, another tri­ 267.48 in the flowing channel, it .such a low velocity during high butary of the Tista, in the year 1903. formed a part zof the dry channel bed. floods in the Tista. when river water the water was deep enough in the Or, in other words, the current of transports a large silt load, a cur­ channel at the railway bridge to water in the flowing channel had de­ rent of water deposits a part, of its bathe in. Now there has been a posited silt and raised the level of .silt load on the channel bed. Thus rise in the channel bed of the Ghish, its banks during the dry season, so on account of the widening of the so that it is within about 5 feet of that the Tista flowed on a ridge, and Tista channel to about 2 miles, there the bottom of the girders, while the not over the lowest parts of its 2 is deposit of silt, leading to a rise channel is dry in the dry season. mile Wide bed. in the level of the Tista channel bed and in flood water levels. A HISTORICAL STUDY The The maximum discharge, carried present course of the Tista channel by the Tista during the very high Rice in Channel Bed does not appear to have existed ar­ flood of 1954, as recorded on August The rise in the level of the Tista ound seven hundred years ago in 24, 1954, has been calculated roughly channel bed has led to the rise in 1206 and I255 A.D., when the Mo- as follows: 1. Discharge Q .spilling over the right hank of the Tista. Spilling area over a length of 2,500 feet and average depth of 1 6", and average velocity 3 feet (per second. Q, 2500 x 1.5 x 3 11.250 cublic feet per second. 2. Discharge Q, pa-swing through the main Tista channel. Sectional area of channel at highest water level 35,500 sq. ft. Average velo­ city, from .surface velocities at 3 points --8 ft. -sees, Q., . 35,500 x 8 284,000 cubic feet per second (eu- secs),

590 hammedan army invaded , the action across the East Himalyas, affected by the floods, to occupy the Karatoya used to be the western captured the water of the Brahma­ country. The several tribal king­ boundary of the Kamarupa King­ putra Kunda, the outfall lake in doms in East Kamarupa, were esta­ dom, and it was the only large river Tibet for the Tsangpo. This natural blished in the 13th century. Durjay, that was crossed by the invading phenomenon appears to have been the capital of Kamarupa on the army. It is probable, therefore, described in the Kalika Purana as banks of the Brahmaputra, must that in the 13th century, Tista water if the sage Parashurama cut a hill have been affected by the abnormal used to flow through the Karatoya, with his axe on the bank of the Bra­ flood, so that it was shifted to Kama- which then had a large channel, as hmaputra Kunda. The sudden exit ta, near Cooch Behar, also in the mentioned by the Mohammedan his­ of an enormous amount of water, 13th. century. torians. stored in the Tsangpo Outfall lake through the Dihong and the Braha- It appears, therefore, probable From the Kalika Purana and from that the Dihong captured the water inscriptions on copper grants of land maputra, must have created an ab­ of the Tsangpo, stored in the Out­ made by ancient kings of Kamarupa, normal flood height in the Brahma­ fall Lake in Tibet, sometime before some interesting facts come to light: putra channel, so that all the inha­ Chapters 81 and 82 of the Kalika bitants of the riverside plains perish­ the 13th century when the tribal Purana give a vivid description of ed. This enabled the hill-tribes kingdoms were established and the a colossal flood in the Brahmapu- who lived on hill tops and were not capital was shifted from Durjay. tra valley in Assam, when the sage (To be Continued) Parashurama cut a suitable outlet with his axe in the hills on the banks of the Brahmaputra Kunda or lake, as a result of which the water stored in the lake found its way into the Brahmaputra channel and the water rose to such a high level that it was difficult to dis­ tinguish between the water of the furious Brahmaputra and that of the sacred lakes in Kamarupa. In ancient times, there was con­ siderable intercourse between India and China, Communication be­ tween Assam and China though existent was exceedingly difficult, being about two months' march through pestilential jungle and mountain, as Hiuen Tsiang the Chinese pilgrim has noted. Never­ theless, communication did exist long before the days of Hiuen Tsiang, as is testified by Chang Kien, Chinese soldier-explorer in Central Asia in the second century B.C. who has stated that there was trade between northeast India and southwest China, through routes among the southern bar­ barian people. Although the sour­ ces of the Indus, the Sutlej, the Ganga etc. were more or less known to be across India's border, it is strange that in spite of the close intercourse between Assam and China, geographers and geo­ logists were not certain even at the end of the 19th. century, of the Tsangpo In Tibet being the upper reach of the Brahmaputra in Assam. From these facts, it appears that the Tsangpo at one time drained its water into a large lake in East Tibet, which has been described in the Kalika Purana as the Brahmaputra Kunda. The Dihong, a north bank tributary of the Brahmaputra, in ex­ tending its channel by cataract 591