May 26, 1956 Tista Flood Problem in West Bengal Embankments No Solution Kumud Bhushan Ray ( Continued from previous issue) BEFORE the Dihong captured the tributaries are dying rivers. level or high water level as compar­ water of the Tsangpo some time A study of rivers in the East Him- ed to that of the Tista. On the before the 13 th century, the akfyas, shows that the Arun , a tri­ other hand, the Tista water spilling Brahmaputra drained the 'rain- butary of the Kosi, has by cataract over its left bank near Barnes, which shadow' area of the Assam action deepened and lengthened its in the high floods of 1954 amounted Valley, north of the Central gorge across the Himalayas and to as much as 140,000 cusecs or Hills of Assam, and carried a small captured the Yaru River valley in about 50 per cent of the discharge discharge. It had, therefore, deve­ Tibet; but the tributaries of the carried by the main Tista channel, loped a tortuous course via Mymen- Tista have not yet been able to cut deposits the whole of its silt load singh Town with an outfall into the across the Himalayas into Tibet. while flowing over the paddy lands larger Meghna, draining the immen­ The deepening and lengthening of in the Barnes-Mainaguri area. The se rainfall on the southern slopes the gorges of the tributaries of the desilted Tista overflow water nearly of the Central Hills. With the cap­ Tista is however, continuing and in doubles the discharge in the Dharla. ture of the Tsangpo water, the Brah­ this process enormous amounts of The clear water helps to downscour maputra carried a much larger dis­ silt load are being added to the the Dharla bed, so that its channel charge, its channel got deepened, waters of the Tista.. and consequently its flood water while its alignment was straighten­ levels have remained lower than ed, from Dhubri to Goalundo past It has been explained that the those of the Tista. Sirajganj Town. velocity of a current of water in the wide channel of the Tista is so low Overflow of Tista Water The improved Brahmaputra chan­ that a part of the enormous amount With a gradual rise in the channel nel appears to have a better outfall of silt in its water is being deposited bed and water levels in the Tista, for the Tista water. A cut-off chan­ on its bed, and there has been a and with little or no rise in those of nel from the improved Brahmaputra gradual rise in the level of its the Karotoya, the Tista water spil­ to the Tista must have been esta­ channel bed, dry season low water ling over its right bank in Jalpaiguri blished sometime in the 13 th century. level and flood season high water Town has a natural tendency to Through this channel the Tista level. The Karotoya, on the other flow into the channels of the Panga, water was being diverted into the hand, being cut off from the Tista Burhi Tista and other tributaries of Brahmaputra. During the latter upland water supply, transports the Karotoya. There have thus part of the 1.8th century, the Tista little silt load. There is thus little been several breaches over the years water stopped flowing through the or no rise in the channel bed, the in the railway line between Jalpai- Karotoya and its diversion through low water level or the high water guri and Haldibari by the overflow the present Tista channel was com­ level in the Karotoya or its tribu- water from the Tista trying to flow pleted. The present position is that tarier,. into the Karotoya. the Karotoya and its tributaries The Dharla. which flows into the The south end B of the embank­ the Panga, Burhi Tista, etc. are larger Jaldhaka River, carries a ment A B (see fig) constructed in completely cut off from upland water small discharge and consequently 1955 along the right Tista bank for supply. As a result of this, Tista transports a small silt load. There the protection of Jalpaigur Town, has water now flows through its present is thus little or no rise in the level been connected to the bank of the channel, while the Karotoya and its of its channel bed, or in its low water railway line between Jalpaiguri and Haldibari. Thus the railway line, south of the point B to Haldibari, will continue to be threatened by overflow water from the Tista, in its tendency to find its way into the tributaries of the Karotoya, while lands between the Tista and the tributaries of the Karotoya will con­ tinue to be submerged during floods. Similarly with a gradual rise in the channel bed and water levels in the Tista and with some lowering in those of the Dharla, the Tista water overflowing its left bank has a natur­ al tendency to flow into the Dharla, between Mainaguri and Mekhliganj. It has been mentioned that in the high floods of 1954 as much as 140, 000 cusees of Tista water spilled over its left bank. Is it any wonder that there have been several breaches in the railway line south of Mainaguri? 611 May 26, 1956 THE ECONOMIC WEEKLY An embankment on the left bank for the irrigation of gardens of these of 'bandals' is that with the increase of the Tista. as proposed on April 4, citizens. of velocity In a current of water at 1956, will probably connect the Tista To prevent submergence of roads the beginning of the flood season, left river bank with the railway line from overflow from road side drains, the channel bed is down scoured and through Mainagurb South of this a Municipality usually deepens a the lines of 'bandar are undermined. connection, the railway line will con­ surface drain. The increased drain­ An improved type of 'bandar, which tinue to be threatened by the Tista age capacity of a narrow and deep is able to maintain, its position and water spilling over its left bank in drain enables it to accommodate and alignment on the channel bed and its tendency to flow into the Dharla, drain away quickly the maximum thus continue its action of narrow­ while the river side lands between discharge for a heavy and prolonged ing and deepening the river channel the Tista and the Dharla will con­ rainfall. To maintain the sectional even in the flood season, has been tinue to be submerged during severe area, the sides and bottom of a drain used in the Beki River in Assam floods, in spite of the embankments. are generally paved with brickwork in 1949. Since then, the improved or concrete and cement plastered. type of 'bandal', which is known as Comparison with Urban Surface The municipal staff also cleans any 'permeable screen', has been used by Drains accumulation of debris in the drain, the NE Railway in rivers in North A study may now be made of cat­ so that its sectional area is main­ Bengal and Assam, for depositing ena or unpaved .surface drains in a tained. silt on selected parts of the wide city. By erosion of their banks, and shallow channels. these drains gradually become wide Narrowing and Deepening a River Permeable Screens in the Tista and shallow. Owing to tins and also Channel A study of an earlier map of on account of the flat, slope avail­ If a wide and shallow river could Jaipaiguri shows that the Tista had able, the velocity of water is very he narrowed and deepened in the a narrower channel. From 1898-1905, low. A current of water deposits, a same way as a municipal surface the author was a student in the part of its silt load, so that there drain, its drainage capacity would Government Zila School. Jaipaiguri. are accumulations of debris in a be increased, maximum discharges He remembers that the,Tista had a drain as islands and sand banks, accommodated within its channel half-a-mile wide channel. The greater round which the drainage flows in and drained away quickly. There depth in this narrow channel made tortuous courses. Such a surface would then be no spilling over banks, if possible for a steamer to ferry drain has inadequate drainage capa­ no overflow and submergence of passengers and vehicles across. He city. Hence during and after a river side lands and no flood also remembers a steamer trip up heavy .and prolonged rainfall, ex­ damages. River channels have been and down the Tista. carrying Tea cess water is incapable of being deepened by dredging, but it is not Planters and high government offi­ quickly drained away and roads get always a practical proposition to do cials of Jaljaiguri. submerged. so. By the use of the 'permeable To prevent flooding of roads, a A river, however, commands a screens' it is possible to narrow and Municipality does not. put up em­ great force, its own current of water, deepen the Tista back to its former bankments along both sides of a which has the power of eroding the width of about half-a-mile. With surface drain. Of course, such em­ material on its channel bed and of an increased drainage capacity in bankments are able to confine the transporting of the silt load thus the narrowed and deepened Tista, drainage coming down from the formed. In the alluvial rivers of the flood water level will be lowered upper parts of the town within the India, this great force has been uti­ and there will be no spilling over drain.