Opinion (Spotlight Weekly)

Kosi, Huang Ho And Flood Disaster

By AB Thapa

There are two rivers in Asia, which were known in the past as the river of sorrow. The Kosi River that flows from Nepal to India was known as the “Sorrow of Bihar”. Similarly the Huang Ho River in China also called the Yellow River was known as the “Sorrow of China”. Both these two rivers were dubbed “River of Sorrow” for inflicting one disaster after another. At present the Kosi and the Yellow River have nothing in common. The Yellow River is already completely controlled whereas the Kosi still remains totally unregulated.

Kosi Flood Disaster

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 have been laid waste as a result 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 hardly anyone in Nepal appears to be concerned. Even the international agencies noted for their active role in studies of the environmental problems and water resources of Nepal have not yet 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.

All the past and present studies and the very recent observations indicate that the Kosi is quickly turning into a hanging river and we are heading for an unprecedented flood disasters. The Kosi would be inflicting such horrific flood disasters one after another The ferocious floods of the Kosi would be frequently hitting very hard particularly the North Bihar and Eastern Nepal wiping out towns and villages, and laying vast area of lands bare with sand deposits. The eastern and the southern boundaries of the flood-affected area could be expected to extend up to the Mahananda River and the Ganges respectively. India's railway and roadway linkages with her northeast states could also be totally severed.

The Kosi River Alluvial Fan

The Kosi River brings a tremendous sediment load from the mountain area. The river is in the process of building a large fan-shaped piedmont deposit. At the head of the fan, at Chatra, the channel consist of boulders and cobbles and pebbles. These coarse materials are hardly carried downstream beyond 15 km from the Chatra, where the coarse materials practically disappear, and the bed materials are composed of medium and fine-grained sediments. The river widens downstream of Chatra, and braiding is characteristic further downstream, where interlacing channels are spread over a width of approximately 6 kilometers. From the head of the fan, the gradient decreases from 1/1000 to 1/5000. At the lower gradients the river divides into several channels occupying a width of as much as 15 kilometers.

Scientists involved in the Kosi study regard that the progressive shifting of the Kosi channel to the west in the past would be followed by the migration to the east. It is equally possible that the Kosi might shift to the low area to the east following the 1730 course by avulsion. One of the most dramatic examples of this is the avulsion and shift of the mouth of the Yellow River 650 km to the north of its former position in 1851. This type of event has occurred many times on the Mississippi River deltas also and, as a result, the Mississippi delta is a complex deposit of several delta lobes each reflecting a different position of the lower Mississippi River. It is said that without the control structures built by the Corps of Engineers, it is likely that the Mississippi River would have by now been following a shorter course to the Golf of Mexico, through the Atchafalaya River channel, which is approximately a 160 km shorter route.

The Yellow River

Huang Ho or Yellow River, is the second largest river in China after the Yangtze, with a total length of 5,464 km. The Huang Ho rises in northern China in a series of springs and lakes in the Kunlun Mountains, south of the Gobi Desert. The river first flows east through deep gorges and then turns northeast at the city of Lanzhou in Gansu Province, from which point it flows for many hundreds of kilometers through the Ordos Desert (Mu Us Shamo), an easterly extension of the Gobi. Turning east, the river then flows due east for about 320 km. . It then turns due south, flowing through a young valley cut in deposits of loamy soil known as loess between Shaanxi and Shanxi provinces. In this portion of its course, the river picks up and carries in suspension yellow silt, which colors the water. The load of sediment is increased by the loess carried into the main stream by a number of tributaries, including the Fen and Wei rivers. The Wei River enters the Huang Ho in the central portion of Shaanxi, and the river then flows east across the northern portion of Henan Province to the plains of northern China.

At the city of Kaifeng, the river enters the plains and changes from a torrent to a meandering stream with a broad channel enclosed by dikes. The dikes were built over a period of centuries to control the river and prevent floods, but they have actually had the opposite effect. Because the large amount of sediment carried by the stream has silted up the bottom of the riverbed, the level of the river has risen, necessitating the construction of higher and higher dikes As a result, in many portions of the lower, or east, course the river is much above the surrounding plain, and when the river level rises, disastrous floods occur.. The floods of the Huang Ho have been so frequent and so devastating that the river is often called China's Sorrow.

History of the Yellow River

In a recently published article in CHINA DAILY, Xiong Lel writes that the Huang Ho was a cradle and killer, s mother and menace. From time immemorial, China had both depended on and dreaded its mighty rivers.

During the Qing Dynasty (1644-1911), control of the Yellow River was thought so critical to dynastic stability that a ministerial post – Governor of Yellow River Affairs- was established. The holder, only second in power to the prime minister, could enter the Forbidden City without dismounting. But in the event of floods, heads would roll.

Dubbed “China’s Sorrow” for inflicting one disaster after another, particularly on the heavily populated lower reaches, until recently the river posed a year-round threat. In summer it flooded, the thaw of its ice also caused havoc every spring with ice runs In the 25 centuries between 602 BC, the fifth year in the reign of King Ding of the Zhou Dynasty, and 1938, the Yellow River breached its dykes fewer than 1,590 times. In the 50 years between 1896 and 1946, there were 210 breaches. In addition, the river’s course to the sea in its lower reaches has shifted from time to time Until recently there were on average two breaches every three years , and a major change of course once a century. Each and every one of these events left its toll on local populations, both their lives and property.

Each inundation has also left a layer of mud, the main culprit of flooding in the first place. For in its middle reaches the big bend of the river passes through a plateau of the fine sediment called loess. When it rains, flash floods literally carry mountains of loess down into the river Over the years, it is said that the sedimentation has raised the riverbed by 5-10 centimeters a year. The Yellow River is thus a “hanging river.”

Difference between Kosi and Huang Ho

There are few striking similarity between the Yellow River and the Kosi. Both these rivers are dubbed “ River of Sorrow”. The annual flow of both these rivers are almost equal. The annual flow of the Yellow River is about 58,000 million cubic meters whereas such annual flow of the Kosi at Barahachetra is only slightly less. It is about 51,000 million cubic meters. As far as the geomorphic and hydraulic characterization is concerned, there is hardly any resemblance between these two rivers. The Kosi, in terms of channel pattern, is a braided river whereas the Yellow River is a meandering river. Despite such differences, scientists are virtually unanimous in their opinion that there is only one way to prevent the Yellow River as well as the Kosi flood disasters. Our only recourse is the provision of storage dams to control the floods.

Rivers can be characterized in terms of channel pattern. Such channel patterns can be straight, meandering, braided, or some combination of these. A braided river like the Kosi would be relatively wide and it would be having poorly defined unstable banks, and it would be characterized by a steep, shallow water course with multiple channel divisions around alluvial islands. There are two primary causes that may be responsible for the braided condition. (1) the stream may be supplied with more sediment than it can carry resulting in deposition of part of the load, and (2) steep slopes, which produce a wide shallow channel where bars and islands form readily.

A meandering stream such as the Upper Mississippi or the Lower Illinois or the Yellow River is the one whose channel alignment consists principally of pronounced bends, the shapes of which have not been determined predominantly by the varying nature of the terrain through which the channel passes. Alluvial channels of all types deviate from a straight alignment. The thalweg oscillates transversely and initiates the formation of bends. A meandering river, in sharp contrast to the braided river carrying the same mean discharge, would be having far smaller longitudinal slope.

Solution to Flood Problem

Since 1949 some eight dams have been built and four more are under construction along its 4,674-kilometre course to control the Yellow River flooding. Among the dams built a long time ago are the dams Liujaxia, Sanmenxia, Longyangxia which were constructed in the years 1968, 1979 and 1988 respectively. It is reported that keeping the Yellow River at bay has saved the China US$ 50 billion.

Now China is facing completely a new type of problem. The Yellow River water is excessively used in irrigation, as a result, the river has started to dry up. Very recently China has embarked on a grandiose plan to divert the surplus flow of the Yangtze River to augment the flow of the Yellow River.

The Kosi River development to resolve the flood problem has emerged as the most important task before us requiring immediate attention of the whole country. Unfortunately very few of us are aware of it. The Kosi challenge is enormous. Our country could be immensely rewarded if we succeeded in resoling the Kosi problem. The Kosi development could make Nepal strong economically. However, our failure could be accompanied by loss of life and property of millions in Nepal and neighbouring countries. Very recently Mr. Navin Singh Khadka has correctly expressed the view on the front page of the weekly magazine NEPALI Times under the title “The mother of all floods” that the catastrophic flood on the Kosi is not a question of “if”, but “when”. Are we ready?