The Sorrow Of Bihar : Kosi River
Pls note: This Article was Writen in June 2004
The Sorrow Of Bihar : Kosi River
By Dr. AB Thapa
There are two rivers in Asia, which were known in the past as the rivers of sorrow. The Huang Ho River in China , which is also called the Yellow River, was known as the “Sorrow of China”. Similarly, the Kosi River that flows from Nepal to India was known as the “ Sorrow of Bihar”. Both these two rivers were named “River of Sorrow” because they had caused widespread human suffering in the past. At present, the Kosi and the Yellow River have nothing in common. The Yellow River is already completely controlled, as a result, it does not anymore pose threat to people. The Kosi still remains totally unregulated. At present, the embankments built on both sides of the Kosi few decades back have temporarily helped to control this river. It is feared that very soon the Kosi would abandon its present course triggering off a new cycle of damages and destructions. After such incident, the Kosi might not anymore be only the sorrow of Bihar. It could be the sorrow of the West Bengal and Bangladesh apart from the terrible havoc the Kosi floods could be playing with the safety of people in southeastern Nepal.
In the Past
The Kosi river known as the river of sorrow of the Bihar shifted from east to west over 12O km in the last 200 years. In the past about 8000 sq. km. of lands had been laid waste because of the sand deposit. In course of shifting, many towns and villages were wiped out, and heavy losses of property, cattle, and human life were inflicted. Fortunately, the embankments built few decades ago temporarily helped to check the lateral shifting of the Kosi. But at present the detention basin upstream of the barrage at Hanumannagar is almost full of sediments. Soon the embankments would be ineffective to control the Kosi floods.
The Kosi river is now on the verge of shifting to the east far away from its present course. The peoples of Nepal and India are heading for a natural disaster of an unprecedented scale. But it appears that only very few in Nepal and India have realized the extent of this danger. It would be unfortunate if the Kosi swing to the east takes the life and property of millions in South Asia by surprise while the governments of Nepal and India would merely be silent spectator.
Rise in Kosi River Bed Level
The Kosi River brings every year an enormous quantity of sediments from its catchments in the mountains. Sir Claude Inglis an expert on Kosi had attributed the shift of the Kosi River channel to excessive sand load carried by the river. Leopold and Maddock considering Kosi behavior had stated that a braided stream will tend to shift laterally at a rate dependent on the rate of accumulation of material being deposited. As one course becomes higher than possible adjacent paths, the river would shift.
Data published in the American Society of Civil Engineering in March, 1966 indicate that in the period between 1938 and 1957 every year on an average about 100 million cubic meters of sediments used to be deposited on the Kosi River bed. The maximum such deposition was around Nirmali in India not far away from the Hanumannagar. There was very big change in sediment deposition pattern immediately after the completion of the Kosi barrage in 1963. The results of the Kosi River channel study for post barrage period have been published by V.C. Galgali, Central Water and Power Research Station, Pune (India), and Gohain & Prakash of Roorke University. All the past studies confirm that the Kosi River bed just upstream of the barrage has significantly aggraded due to sediment deposition. On account of ponding, sediment deposition had occurred, flattening the bed gradient. The bed slope of the river in the pond area was abut 0.61 m per km in the year 1956 prior to construction of the barrage, which became flatter to about 0.42 m per km in the year 1969, ie in six years of the functioning of the barrage. Studies were made to determine the sediment deposition based on post flood 1963 and 1970 surveys These studies indicated that about 35 million cu.m. sediments had deposited in the pond length of about 10 km upstream of the barrage, giving an average depth of about 0.4 m in about 8 years with a rate of bed level rise at about 0.05 m per annum.
Few years after the commissioning of the Kosi barrage there was a big flood in 1968. A discharge of about 25,000 cumecs was recorded. The flood at that time did not pose any serious threat. At present the conditions might be altogether different. It is said that whenever the discharge exceeds 9,000 cumecs , which is fairly common, the whole area between the embankments is submerged. Such observations raise the fear that a flood similar to 1968 flood in magnitude could prove to be catastrophic. It should be further remembered that the 1968 Kosi flood is not exceptionally rare. A flood of this magnitude has already been observed twice within the last 50 years. Fortunately in course of the last 35 years the maximum flood discharge of the Kosi River has not exceeded 16,000 cumecs.
Embankments Would be Ineffective
Embankments built a few decades ago temporarily helped to check the lateral shifting of the Kosi. The detention basin upstream of the Kosi barrage near Hanumannagar is going to be very soon full. After that the embankments would be ineffective to prevent the lateral shifting of the Kosi. It is predicted that the Kosi would again take its 1732 course. The farthest position of the new course of the Kosi is expected to be about 120 km away from its present course. The swing of the Kosi river to the east could be sudden and almost unexpected because nobody yet exactly knows when it is going to happen. The people would be completely taken by surprise. So the loss of life could be very high. In a similar type of 1938 flood incident of the Yellow River in China the number of people killed alone was about half a million. It does not need to be further explained that such shifting of the Kosi to the east would be a biggest disaster for the whole region. Generally, the flood damages are temporary in nature but the Kosi flood damages would be widespread and also permanent in nature. Mr. Shilling Feld an expert on Kosi, has warned a longtime ago that the eastward movement of the Kosi will be in one big swing accompanied with great loss of life and property.
Resolving the Flood Problem
Provision of dams in the drainage area with very big storage volume is the only lasting solution to the Kosi flood problem. It is the opinion of the renowned experts and scientists involved on the Kosi study in the past. We can draw such lesson from the past experience of China also. It can be concluded that there are not any substitutes for the large storage dams to control the Kosi floods. Thus, our only recourse is storage dam. The storage dams should be provided in time. Unfortunately, some peoples in Nepal and India have misgivings about the Kosi dams. Such misgivings are unfounded and they are often the result of present global disenchantment with the high dams particularly for the generation of hydroelectricity. In case of the Kosi dams this type of notion is completely misplaced. The life and property of too many peoples in Nepal and India would be at great risk if the Kosi dams are not built in time.
Learning to Live with the Floods
Some people in Nepal and India have misgivings about storage dams. They regard that we should learn to live with the floods, therefore, it is not necessary to build storage dams to control the floods. The core issues often raised against the flood control embankments and dams in Kosi drainage area do not appear to be realistic. Some subscribe to the principle that the Kosi should get back its original route to the Ganga. One would certainly be at a great loss to determine the original route of the Kosi to the Ganga. The Kosi route had shifted from east to west over a distance of 120 kms in the last 200 years.
In almost all the cases when there is surplus water in the river, flooding results. It is a well known phenomenon in hydraulic engineering.. The Elbe and Rhine floods reported few years back in our newspapers come under this category. The Yantze River floods are also of similar nature. The flood damages are not permanent in nature. Some people try to attribute future Kosi floods also to this type of hydraulic phenomenon. Unfortunately, the Kosi flood feared to wipe out in future vast area of densely populated lands in our region is altogether different in nature. Unlike the above mentioned floods in Europe and China, the Kosi flood damages would be virtually permanent in nature.
The 1997 Indo-Nepal Study Agreement
In 1997 an agreement was signed between Nepal and India to carry out feasibility studies of the Sun-Kosi project and the Kosi project along with a navigation canal linking Nepal with the seaport. This agreement is a substantial modification to the earlier understanding reached between the Prime ministers of Nepal and India that covered only the Kosi high dam. The modification was made based on the findings of Nepal explained to Indian side in the meeting. There is a very close interrelationship between the Sun-Kosi and the Kosi projects. This interrelationship required the inclusion of the Sun-Kosi dam project in the Kosi development. Even a simple analysis of both these projects clearly illustrates the following points that help to explain why the Sun-Kosi project should be built first, and as a result, the feasibility study of the Sun-Kosi Project had to be completed as soon as possible. (a) The diversion of the Sun-Kosi river at Kurule is the most important project of Nepal for agriculture development in near future. . It can be said based on the Karnali feasibility study that North Bihar would be getting for free about 65% of the water diverted from the Sun-Kosi reservoir for irrigation in Nepal’s Eastern Terai as return flow. Moreover, the stored Sun-Kosi water diverted in surplus to the need for irrigation in Nepal for generation of power would also be freely available to irrigate vast area of lands in North Bihar. This very important project would be precluded forever after the completion of the construction of the Kosi high dam project. Fortunately, the Kosi high dam project can be built even after the completion of the construction of the Sun-Kosi high dam project. (b) The Kosi high dam along with a navigation canal to link Nepal with seaport is a very big project. Needless to explain that navigation canal would be extremely important for future development of Nepal as well as North Bihar. It will take long time to implement this project. But the Kosi river is on the verge of shifting to the east. The Sun-Kosi dam project could control the Kosi floods in the interim period till the Kosi high dam is completed. (c) Very serious downstream degradation problems could be expected to arise after the completion of storage dam projects. It is due to release of clear water from the reservoir in big quantity. Such acute degradation problem was observed in Boulder dam of the USA. The river bed in the 77 mile canyon reach had been lowered between 6 and 14 feet. Owing to the exposure of rock ledges the river became stable. However, at about 130 kilometers away, the riverbed rose by six metres necessitating the construction of very expensive flood control structures. Similar phenomenon could be expected after the completion of the Kosi high dam also. The Sun-Kosi high dam built to control the floods in the interim period could help to reduce downstream degradation. It could also help to determine with greater accuracy the volume of flood regulation storage.
Mr. F.A. Shilling Feld, a renowned expert on Kosi study, had made a chilling forecast a long time ago “ The westward movement of the Kosi oscillation (in the past) is slow and is in a series of steps, each of which is attended with damage to property of temporary nature. The eastward movement (in future) of the oscillation will probably be accompanied with great loss of life and property.” It is hoped that the governments of Nepal and India would take up the Kosi development matters seriously.
(Dr. Thapa writes on water resources)