Bharat Jhunjhunwala
China is facing the worst floods in hundred years though it made the largest numbers of dams in the world. India too is facing floods in Bihar despite having arrested floodwaters in the Tehri Dam. Assam is regularly facing severe seasonal floods. The reason is that we consider rivers only as carriers of water and ignore their role as the carriers of sediments.
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We forget that the landmass from Haridwar to Kolkata has been made by the sediments brought by the Ganga. The water of the Ganga has been spreading all around for thousands of years and depositing the sediments. These sediments have become the states of Uttar Pradesh, Bihar and West Bengal. Yet, floods also cause human suffering. Question is how should we deal with this?
Ganga has the highest load of sediments among the major rivers. She deposits sediments in her channel every year. Then, these sediments are pushed to the sea during major floods that come every five or ten years and the channel is restored to its earlier depths and high capacities to carry water. However, we have stopped such major floods by making the Tehri Dam and removing much water from the Haridwar and Narora barrages for irrigation.
As a result, the sediments being deposited in her channel every year are no longer being pushed to the sea; the level of the channel is gradually rising; the Ganga’s capacity to carry the floodwaters is getting reduced; and even a ‘small’ flood now inundates the banks and causes huge damage as is seen in Bihar today. We have actually increased the flood fury by making the Tehri Dam.
The Farakka Barrage has made the problem worse. Hydrologists tell us that even making the pillars of a bridge causes serious obstruction to the flow of the river and reduces its velocity and ability to carry the floodwaters. It follows that the velocity of the Ganga is reduced even if all the gates of the Farakka Barrage are opened.
The reduced velocity leads to the river depositing more of sediments upstream of Farakka. This leads to a double-reduction of the capacity of the Ganga to carry the floodwaters. The reduction in velocity directly reduces the extent of water that she can carry to the sea; and a reduction in the depth of the channel further reduces the extent of water she can carry. As a result, the floods in Bihar are increasing.
Some scientists believe that the flow of the Ganga has been reduced from Barh to Farakka while others say the flow has been reduced from Buxar onwards. The capacity of the tributaries like Kosi and Gandak has been reduced in tandem because the Ganga cannot accept the water brought by them just as it is difficult to enter a Second Class railway coach that is already full. No wonder, Chief Minister Nitish Kumar has been seeking a reassessment of the relevance of Farakka Barrage.
Two studies got done by the Tehri Hydro Development Corporation found that the reservoir of the dam will get completely filled up in 140 to 170 years. Thereafter, we will not be able to hold any water and the major floods will be restored. However, by that time, the sediments deposited in the riverbed would have got stabilised and hardened and the major floods may no longer be able to push the sediments to the sea as they can do today. In this way, we are putting our future generations in peril by our penchant for controlling the floods today.
Another fateful consequence of arresting the sediments in the Tehri Dam is that the sediments that would have reached the Sunderbans are no longer reaching there. This is resulting in huge erosion. The sea has a natural hunger for sediments and it begins to eat the land if its hunger is not met. The erosion of the Sunderbans is partly due to the rise in sea level due to global warming but also partly due to the deprivation of the inflow of sediments from the Ganga. It can be said that the Tehri Dam and Haridwar and Narora Barrages are ‘eating’ away the sacred land by opening the path for the sea to eat our land.
Indeed, the Tehri Dam is providing drinking water to Delhi and these barrages are providing irrigation and enhancing our food security—but at the cost of loss of the sacred land.
The engineers of Bihar are not behind. They have made a number of embankments on the sides of the rivers. They wanted to restrict the flow of the river to her channel so that the floodwaters did not spread and create havoc. The people were surely helped. But, for how long? The sediments brought by the rivers got deposited between the embankments and that is leading to the rise in the level of the riverbeds.
The engineers raised the height of the embankment in parallel. Soon, the level of the riverbed became higher than the surrounding land. The river now flows above the ground like the Metro Rail. And, when the embankments break, as they necessarily have to sooner or later, then the water gushes out and inundates much larger area because the land between two rivers becomes like a bowl and the floodwaters cannot now flow to the sea since their pathways are obstructed by the raised river courses.
We will have to learn to live with the floods. I had an occasion to study the floods in Gorakhpur in the 90s. Local people told me that previously the floods were welcome. Villages were made on raised lands and people lived safely in their houses during the floods. The floodwaters used to flow like a sheet of water. They brought sediments that fertilised the soil. They used to grow certain varieties of paddy that increased in height as the floodwaters rose. The floods would soon recede and they got not only paddy crops but floods fertilised soil for their rabi crop.
We will have to revert to this approach of ‘living with the floods.’ We will have to remove the dams, barrages and embankments. We can still obtain drinking water for Delhi and irrigate our fields by undertaking groundwater recharge in the plains of Uttar Pradesh. We can store about 76 billion cubic meters (cumecs) of water in the groundwater aquifers of UP. The 2.6 billion cumecs stored in the Tehri Dam is a pittance, by comparison.
However, the engineers love large toys like dams, barrages and embankments because of obvious reasons but these will only push us into deeper floods and human sufferings. India and China have to choose between toys for our engineers and safety of our people with protection of the sacred land.
The writer is a former Professor of Economics at IIM Bangalore.
