Opinion (Spotlight Weekly)

CHINESE EXPERIENCE: Averting Kosi Disaster

By Dr. AB Thapa

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. It is feared 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. The shifting of the Kosi to the east could be a biggest disaster for the whole region. Perhaps in terms of loss of life and property the imminent Kosi flood disaster might even exceed the recent Asian Tsunami Disaster that struck our region.

Yellow River Flood Problem

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

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 no 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. In its middle reaches 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”

Analogy Between Kosi And Yellow River

Dr. K.L. Rao former Irrigation and Power Minister, Government of India has written in his book “ India’s Water Wealth” about the Yellow River flood problem. He has written that in China, practically all the rivers have a flood problem. The most important one, the Yellow River has almost a similar maximum discharge as the Kosi.

Huang Ho or Yellow River, is the second largest river in China after the Yangtze, with a total length of 5,464 km. The Yellow River 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. 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 Yellow River 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 Yellow River have been so frequent and so devastating that the river is often called China's Sorrow.

River Channel Hydraulics

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.

How Yellow River Flood Problem Solved

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.

Resolving the Kosi Flood Problem

We have already succeeded in convincing India of the Kosi flood danger in a bilateral talk held in Kathmandu in 1997. It resulted in signing the agreement to conduct jointly the detailed feasibility studies of the Sun-Kosi Project, Kosi Project and the Kosi Navigation Canal linking Nepal with the seaport.

Provision of dams in the drainage area with very big storage volume is the only lasting solution to resolve the Kosi flood problem. We can draw such lesson from the past experience of China. It is also the opinion of the renowned experts and scientists involved on the Kosi study in the past. It can be concluded that there are not any substitutes for the large storage dams to control the Kosi.

(Dr. Thapa writes on water resources)