September 19, 1953 The Problem of the Kosi Kumud Bhushum Ray

N an appeal issued on August 23, down the inclined plane of the land, flattened. Thus with the erosion of I 1953, Shri Jawaharlal Nehru under the motive force of gravity. river banks, the HMD of its chan­ asked for generous contributions to The average velocity of flow through nel is gradually decreased, while the the Prime Minister's National Re­ a river channel has been expressed slope of water surface is also gra­ lief Fund. It is stated therein: by the Chezzy Formula: dually flattened. From the formula "The Kosi River in Bihar, v=c r s, it is evident that a gra­ which has misbehaved so often in dual decrease in the HMD r, and a where, v is the velocity in feet per the past, has this year caused un­ flattening of the slope of water sur­ second; precedented floods and a consi­ face s, both lead to a gradual de­ r is the HMD (hydraulic derable part of Bihar has been crease in velocity. mean depth), being under water." The Kosi waters carry the largest equal to the sectional The area submerged by the Kosi annual sediment load of 7,308 tons area divided by the per sq mile of its catchment, as com­ waters in the flood season of 1953 wetted border; is 1,085 square miles. As reported pared to all other rivers of the world, s is the slope of water sur­ where such records are maintained. in the Statesman of August 31, " first face, being equal to the tentative reports reaching the Gov­ Hence due to uncontrolled erosion of difference in level be­ river banks and consequent reduction ernment through official channels tween two points in a on the one-month-old North Bihar in velocity, a considerable part of river course, divided by this large sediment load of the Kosi floods, disclose a grim picture of ex­ the length between these tensive damage, estimated at Rs 21 waters is deposited on the Kosi bed, two points along the whose level thus goes on rising at crores." It is also stated that river; " relief operations within the last a rapid rate. With a gradual rise and, c is the coefficient, vary­ in the river bed, the water level in one month have cost the State over ing with the different Rs 1,00,20,000, but this is expected the Kosi channel goes on gradually conditions of flow in a rising, until river banks are over­ to go up beyond Rs 2 crores within river channel. the next few weeks ". topped and riverside lands are sub­ These reports, however, fail to A river's primary function is merged. This explains the floods carry any notion of the horrors of drainage of water and its secondary from the Kosi. a flood. A flood goes on and on function is transportation of the MISHEHAVIOUR OF THE KOSI for days and sometimes weeks and sediment load to its outfall. A river The remark that the Kosi " has then it leaves a whole area plastered is able to perform its function of misbehaved often in the past ", down in mud and stench. One has drainage of water, only if it can which occurs in the Prime Minister's to imagine the heartache of the in­ maintain its channel in good order; appeal, will be apparent from a habitants as they return to their ' and for this, none of the sediment study of the map of the Kosi homes and lands, which many have load must deposit permanently on River Basin. In 1731, the Kosi had spent their Jives to build and any part of its channel, but must its channel along the Kali Kosi, acquire. Hundreds of houses, which be transported to its outfall. As the and in 1770 along the Livari. From have collapsed iti the submerged power of transportation of sediment 1807 to 1839 Kosi waters flowed area, will have to be rebuilt. Da­ of running water varies in geome­ along the Dhamdaha, from 1840 maged roads, railways, etc, will have trical progression with variations in to 1873 along the Hiran, from 1874 to be repaired. Moreover, floods its velocity, the velocity of flow in to 1892 along the Sursar, from bring in their wake hunger, disease the river channel must remain high 1893 to 1921 along the Mircha, and misery, and the people affected in the flood season, when river water from 1922 to 1936 along the Dhu- by floods have to face stark misery transports a large sediment load, san, from 1926 to 1948 along the after the flood is over. in an alluvial plain, a river erodes Tilabeh, in 1933 along the Dhemra, its banks. Erosion of banks increases and now Kosi waters arc flowing WHY FLOODS? the channel section, so that the along the lower reach of the Tif- velocity of flow is decreased, and a juga River. Such shiftings of the A river channel is formed in the considerable part of the sediment process of drainage of water from Kosi has been rightly called a mis­ load is deposited on the river bed, behaviour. the river catchment to its outfall raising its level. Thus erosion of into the sea. The fundamental law river banks makes the channel wider SHIFTING OF CHANNEL of hydraulics, by Domenico Gugli- and shallower. A wider and shal­ It has been explained that 'un­ elmini, is: lower channel has lesser HMD than controlled erosion of river banks An alluvial river automatically a narrower and deeper channel of causes widening and shallowing of adjusts its channel to its flow re­ the same sectional area. Erosion of a channel, as well as lengthening quirements. river banks also leads to the forma­ of its course by the development But if that is so, how is it that the tion of bends, so that the length of of bends and a tortuous course, Kosi has not been able to adjust its the river course between two points both of which lead to decrease in channel so that it may accommo­ on the river is increased; but as the the velocity of flow; the gradual date and drain away quickly the level of these two points remain decrease in velocity causes heavy maximum discharge? River water, practically the same, with an in­ deposit of the large sediment load like any other moving body, has a crease in the length, the slope of of the Kosi waters, so that there tendency to move in a straight line water surface becomes gradually is rapid rise in the river bed and 1028 THE ECONOMIC WEEKLY September 19, 1953 consequently of the water level, New Kosi. By the same process, nels, whose drainage capacity is leading to overtopping of river one eastern channel after another very limited. This explains, why banks, overflow and submergence was choked up with deposit of "a considerable part of Bihar" of riverside lands. In 1731, as al­ sediment and got abandoned, while within the region ABC remain sub- ready mentioned, Kosi waters flow­ one western channel after another merged under Kosi overflow waters, ed along the Kali Kosi, the distance got improved by the addition oi There is also the further danger, from Chatra to the outfall into ' Kosi overflow waters and became that if erosion of the present Kosi the Ganga along the Kali Kosi the New Kosi. Erosion of river river banks is allowed to go on channel being about 110 miles. As banks is thus the cause of the shift- uncontrolled, its discharging capa­ a result of the uncontrolled erosion ings of channel of the Kosi. city will deteriorate even more; so of river banks, there was overflow And now there appears to he no that overflow from its channel will from the Kali Kosi which found more suitable western channel left further increase, and a greater area its way into the parallel western to be improved by the Kosi over­ of North Bihar will be submerged channel, the Livari. The overflow flow. The present Kosi channel under a greater depth of water and diversion of water from the along ACB has a length of about during the flood season. This will Kali Kosi led to its decadence; 170 miles, nearly one and half times continue, until one of the former while the addition of the overflow that of the Kali Kosi along AB. abandoned channels of the Kosi, waters into the Livari led to its The slope of water surface along which has a straighter alignment improvement. With a lessening of the channel ACB (see sketch map) and a better out fall, is opened by velocity, there was deposit of sedi­ is thus much flatter than that tile larger volume of Kosi overflow ment, the Kali Kosi channel got through the channel AR, so that waters flowing through it. choked up and was abandoned; the velocity of flow through the and Kosi waters flowed through present channel is much less. No AN EMBANKMENT WEST OF KOSI the improved channel of the Livari, wonder, the present Kosi channel There is a proposal to construct about the year 1770. But in the cannot accommodate and drain an embankment along the right or Livari also, there was uncontrolled away quickly the flood discharge, west bank of the Kosi channel be­ erosion of river banks, so that the so that with the start of the flood tween A and C. Such an embank­ same process was repeated, the season there is overtopping of river ment will, no doubt, prevent sub­ Livari channel got choked up, the banks, overflow and submergence mergence of lands west of the Dhamclalia channel got improved, of land and flood damages. The Kosi. But as a result of this, the until the Livari was abandoned Kosi River Basin ABC has become whole of the Kosi overflow will and the Dhamdaha became the a region of choked up river chan­ have to go eastward, and the parts oi North Bihar in the area ABC will have to remain submerged under a greater depth of water and for a longer1 time than at present. It may he mentioned here, that this embankment will not prevent ero­ sion of the Kosi river hanks, a process which is at the root of the past misbehaviour of the Kosi river. Neither will the embank­ ment effect any improvement of the Kosi channel, enabling it to ac com­ modate and chain away quickly its maximum flood discharges. Such an embankment, as already ex­ plained, will only protect the lands to the west from inundations from the Kosi overflow waters. IMPROVEMENT OF RIVER CHANNEL If a river channel is able to ac­ commodate ami drain away quickly its maximum flood discharge, there is then no overtopping of river- banks, no overflow, and no flood damages. A narrower and deeper channel with a straighter align­ ment, has a greater HMD and a steeper slope of water surface and therefore develops a greater velo­ city and has a greater discharging capacity than a w i d e r a n d shallower channel of the same sectional an a with a tortuous alignment. The latter has a lesser HMD and a flatter slope of water surfare and therefore develops a lesser velocity and has a lesser dis- 1029 September 19, 1953 THE ECONOMIC WEEKLY charging capacity. improvement This explains the existence of banks' is made two and half times of a river channel can be effected stable channels in the Missouri and the width of the narrowed river. by helping a river to form a nar­ the Mississippi, about which Pickels Each pair of ' guide banks' stabi­ rower and deeper channel with a wrote in 1941: lises the river channel for a length straighter alignment. The greater " As an example, there is a of six to eight times the narrowed velocity developed in such an im­ straight stretch of the Missouri width of the river. Hence the dis­ proved channel increases the dis­ river above the mouth of the tance apart between successive pairs charging capacity, so that maxi­ Little Sioux river, where the of ' guide banks' should be made mum discharges are accommodated banks on both sides are of sand, six to eight times the narrowed and drained away quickly. There unprotected by revetment, yet width of the Kosi. The straighten­ is then no overflow, and flood this stretch has not changed its ing effect, caused by the guiding damage from the river is thus position in more than 50 years. action of the pair of 'guide prevented. Also, the channel of the Missis­ banks', together with the drawing in action of the next downstream PARALLEL RIVER BANKS sippi river between St Louis and Cape Girardeau and below New pair of ' guide banks ' in the Kosi, In his book Various Problems Orleans is unusually straight and will prevent erosion of the unpro­ connected with the Maintenance of stable." Drainage and Flood tected concave river bank in be­ the Rivers and Drainage System of Control Engineering, page 333. tween, and neutralise the natural the Gangetic Delta (ICJ2O) C tendency of the bend to migrate Addams-Williams, a Chief Engi­ When the Kosi River is guided downstream. neer, Bengal PWD, wrote: to a narrow and deep channel with For the 170 miles of the Kosi parallel river banks, by means of " In a wide channel, the cur­ River, about 50 pairs of ' guide parallel lines of ' permeable banks' will be necessary, the cost rent is liable to content rate into screens ', water flowing with a high a local gutter; so why not pro­ of which is about Rs 30 crores. velocity parallel to these erodable But as already mentioned, such vide what the river requires at banks will not cause appreciable the outset? " ' guide banks' are necessary only scour. With these newly formed in the vicinity of important cities. It is possible to guide a river to parallel river banks, the Kosi will concentrate into a local gutter, have a stable channel. The high TAMING THE KOSI velocity through such a narrow that is, into a narrow and deep Channel stabilisation by a series channel. To estimate the width of and deep channel will increase the discharging capacity of the Kosi, of parallel ' permeable screens' this narrow channel, the maximum and making these newly formed depth of scour in a straight reach so that it will be able to accom­ modate and drain away quickly the parallel river banks permanent by of the river has to be accurately a series of pairs of 4 guide banks', determined. By allowing for the maximum discharge, without over­ topping of river banks. There will for the whole 170 miles length of river bed being downscoured to the the Kosi River will cost about depth of maximum scour, the nar­ then be no overflow, no submerg­ ence of riverside lands and no flood Rs 31 crores, as compared to the rowest width to which the river SINGLE Kosi Dam, which has may be guided is calculated for the damages. With no appreciable erosion of river banks, channel been variously estimated to cost slope of water surface in that reach. between Rs 66 and Rs 100 crores. P a r a l l e l lines of permeable stabilisation will be ensured in the Kosi. In the Tennessee Valley, where screens' are then laid along the dams and reservoirs have been river bed' at the distance apart thus The length of each ' permeable screen' is two and half times the extensively used for river control, calculated. The lesser velocity, there are nine dams on the Ten­ caused by the ' permeable screens' width of the narrowed Kosi, and the distance apart between adja­ nessee main river and twenty-one in the part of the river channel dams have been constructed to between the line of ' permeable cent pairs of parallel ' permeable screens' is from six to eight times control the Tennessee headwaters. screens' and the original river It must be realised, that to control banks, leads to deposit of sediment the width of the narrowed Kosi, The number of pairs of parallel the Kosi headwaters, " a scientific load on the river bed with the mesh of dams" is also necessary, formation of new parallel river ' permeable screens', necessary for channel stabilisation of 170 miles of the cost of which would be ap­ banks; while the higher velocity in palling. The proposal to con­ the narrower channel, between the the Kosi along ACB, is about 50. The cost of these works will be struct the SINGLE Kosi Dam was parallel lines of ' permeable made in 1947; but although six r about Rs 1 ¼ crores, which is less screens causes downscouring of years have passed since then, at­ the river bed. A narrow and deep than the cost of relief operations in North Bihar in the flood season tempts appear to be only being channel with parallel river banks is made to design a dam at a cost of thus formed. 1953, and is a fraction of the " extensive damages estimated at Rs 66 crores, instead of at Rs 100 crores. It will take many decades CHANNEL STABILISATION Rs 21 crores ". before the country can find the In the book River Training and PAIRS OF GUIDE BANKS finance to build " a scientific mesh Control, by Spring, Government of The newly formed parallel river of dams " to control the Kosi head­ India Technical Paper No. 153 banks of the Kosi may be made waters. But must North Bihar suf­ (1903) in Chapter IV, para 9, permanent, in the vicinity of im­ fer annually from flood damages page 13, it is stated: portant cities, by constructing a from the Kosi for these decades? "A comparatively rapid cur­ series of pairs of ' guide banks'. It is true that channel stabilisation rent may flow alongside and River alignments at several railway will not generate hydro-electric parallel to an erodable bank bridges have been made permanent power, nor provide water for irri­ without causing it to cave appre­ by a pair of ' guide banks.' The gation. But channel stabilisation ciably." length of each of these 'guide will: 1230 THE ECONOMIC WEEKLY September 19, 1953 1. Provide tor prevention of flood damages; 2. Prevent destruction of fertile riverside lands by erosion; 3. Reclaim the wide wastes of sandy river bed as fertile land ; 4. Provide perennial navigation in the deepened river chan­ nel; 5. Lower the dry season water level in the deepened river channel and thereby ensure natural drainage from river­ side swamps; 6. Make available these swamps as fertile land; and 7. Eradicate malaria, as mos­ quitoes will not breed in the drained swamps. With channel stabilisation in the 170 miles length of the Kosi, effected at a cost of about Rs 1¼ crores, works for which can be taken up simultaneously all along the river, or only in the lengths most affected by flood damages, and completed in about three years' time, the inhabitants of North Bihar will have freedom from fear of annual flood damages. Another advantage of this solution is that the materials required for the con­ struction of t h e ' permeable screens' or the ' guide banks '— bamboos, sal bullahs, mild steel rods and wires, wire ropes, bricks and stone—are all available within the country. Labour and super­ vision necessary for such works are also available within the country. This will do away with the prob­ lem of foreign exchange.

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