The Brahmaputra River Basin is one of the most problematic in India. The problems are as follows -
1. There are huge floods during the monsoons that regularly wreck havoc every year.
2. There is water scarcity and sometimes drought in summer.
3. The main stem in the form of the River Siang originates in the Tibetan plateau which is in China and so there are concerns with regard to China building dams on the Tsangpo as the river is known in Tibet and reducing the flow into India.
The problem of floods has been there from the beginning because the basin receives heavy rainfall during the monsoons amounting to 3000 mm or more per annum. However, over the years increase in human population and anthropogenic activities in the basin, especially in the upper catchments of the basin in Arunachal Pradesh has led to huge deforestation, soil erosion and runoff. Moreover, even though most of this rainfall was always concentrated in the monsoons, of late the frequency of heavy storms and cloudbursts has increased resulting in heavier runoffs. The net result is that there are heavy floods. The approach of the water resources department has been one of ignorance. Ignorance regarding the basic dynamics of the river. A river depends heavily on its underlying hydrogeology. The precipitation during the monsoons gets recharged into the ground by the forests and their underfloor, filling up the aquifers during the monsoons. These aquifers then release their stored water throughout the year as base return flow that keeps the rivers flowing. Therefore if due to deforestation natural recharge into aquifers is reduced then not only are there floods but also the flow dries up during the rest of the year and in extreme cases there are droughts in summer. Moreover, due to soil erosion the sediment load has increased constricting the river channel and leading to erosion of the banks and the widening of the river. So all the rivers that contribute to the Brahmaputra have wide river beds which overflow during the monsoons and are dry afterwards. The three longest river bridges in India are all across the Brahmaputra and its tributaries, the Dibang and Lohit and are 6 to 9 kms long.
What is the plan to tackle this problem that the ignoramus's in the water resource establishment, including those in the Centre for Brahmaputra Studies in the Indian Institute of Technology, Guwahati have drawn up? It is the usual one of building several big dams for storing the excess water in the monsoons for flood control and to build embankments on the sides of the rivers to contain the river flow. While control of floods through dams has turned out to be a failure globally primarily because the valleys in the upper reaches of rivers are narrow and so do not have much water holding capacity as compared to the monsoon flow, the mighty Brahmaputra has repeatedly breached the embankments. So even if only one dam is under construction so far on the tributary Subansiri in Arunachal Pradesh, this along with others that are proposed are not going to control floods in any big way. Instead, as was the case in Kerala a few years ago, during heavy and unprecedented downpours the extra water released from the dams tend to aggravate the floods.
Another daft proposal is to link the Brahmaputra to the Ganga and thereafter to the southern rivers under the river linking project. The problem with this is that there is a huge ridge between the Brahmaputra and Ganga valleys and then again there are huge ridges between the Ganga valley and the southern river valleys. These ridges cannot be crossed by gravity flow. Linking of rivers is feasible only when the valley are in parallel with a ridge running between them. Then one river can be dammed in its upper reaches and the water can be diverted from it through a canal by gravity to the other river down stream. This is what has been done in the case of the Narmada and the Sabarmati river valleys in Gujarat. However, this is not possible with the Brahmaputra and the Ganga river valleys because they are not parallel.
The third problem of China building dams on the Tsangpo and reducing the flow into India will be environmentally damaging to the river but it will not affect the flow significantly because the Tsangpo contributes just 5 percent of the total annual flow of the Brahmaputra which is mainly made up of the monsoon flow from its tributaries arising in Arunachal Pradesh and Bhutan.
Therefore, the thrust of flood prevention should be in ensuring afforestation and artificial recharge through soil conservation measures in the hilly catchments so that as much as possible of the monsoon precipitation is recharged into the underground aquifers. This will also ensure year round flow in the river and solve the problem of droughts in summer. The most rational way to conserve and use water resources in a basin is to do it in the watersheds in situ as far as is possible. Planning should start from the uppemost ridges and work down to the drainage line. This is a challenging task because of the steep terrain and it involves community participation by the people living in these hills. However, investment in such natural and artificial recharge programmes are much less than that required for building dams and embankments and also provides livelihoods to the people and conserves the environment.
Unfortunately, the ignoramuses who control the water resource management in this country are loathe to give up their idiotic privileges and powers and so they have now embarked on a rafting expedition down the river from the place where it enters India from China to the place where it leaves India to enter Bangladesh to study the sediments and see if they cannot be used to build roads along the banks of the river!!
Where ignorance is bliss, 'tis folly to be wise as the poet Thomas Gray wrote.