Embankments or flood-walls: It is another common Engineering measure. Embankments do not reduce the volume of flow of a river during floods. Rather, it is a commonly used method to confine the flood water of a river within a limited area around its channel thereby giving reasonable protection to the inhabited/cultivated areas beyond it in the countryside. It is a direct and cost-effective method that has been used for thousands of years by man.
Most embankments in the Brahmaputra and its tributaries were constructed after India’s independence i.e. 1947 and before the year 1980 as a short term measure. As per the website of the Water Resources Department (WRD), Assam, the total length of embankment constructed along the Brahmaputra and its tributaries is 4473.82 Km. They cover most of the problematic areas of the valley that needed protection from floods by the Brahmaputra as well as its tributaries. However, demand from the public for construction of embankment in smaller and less problematic areas keeps coming even now and many new embankments constructed after 1980.
Some experts and critics are of the opinion that embankments have caused more harm than help. It is cited that prior to the construction of embankments, the Brahmaputra river used to spread out in the valley during floods. Due to this, the depth of submergence was not high and therefore, losses were minimal. Examples are cited to a pre-independent era when floods were not such havoc in the valley. It is also cited that whenever there was a breach in an embankment, it led to great losses of life and property which may not have occurred without the existence of these embankments. Further, the rise of the river bed due to siltation in an embanked river is faster as entire siltation occurs between the embankments.
In this regard, it may be mentioned that most embankments in the Brahmaputra Valley were constructed four to five decades ago and outlived their lives. Beside rain cuts and soil erosion over this period, encroachment by the construction of houses on its slope, cutting it for road crossings, growing of trees, bamboo, and different vegetables, etc on it are other reasons for damages to the embankments. The maintenance of embankments in the valley has been poor due to the financial constraints of the State. Low specifications of early embankments, poor binding quality of soil used in some locations, etc have also contributed to their failures. For these reasons, breaches in embankments of the Brahmaputra Valley are a common feature during large floods.
Notwithstanding the above, embankments in Assam have protected thousands of flood-prone villages, assured cultivation from flood damages in vast areas for decades, protected many important townships including Dibrugarh town and increased cultivable area commensurate with the growth of population in the valley. The population in Assam has grown many-fold since the 1950s and today a large population lives in new areas not inhabited earlier. Under the protection of these embankments, villages have developed in areas close to Brahmaputra and different tributaries where there were none before. It is to be noted that only limited and relatively higher areas of the valley were occupied by people prior to 1947. There is no place in the valley to rehabilitate inhabitants of all such new protected areas in case embankments are done away with today.
It is also to be noted that modern amenities, roads, and railways, etc have been built all over the state since independence. These already developed infrastructures need protection from floods which is provided by the embankments in many cases. People will refuse to travel today from Dibrugarh to Dhakuakhana by a boat as was done in the 1950s! Therefore, thinking of a situation without embankment in the Brahmaputra valley is not an option today. Especially so as the most potent option of reduction of flood volume in Brahmaputra river through storage reservoirs remains still a distant dream because of the non-convergence of interest of stakeholders in the fray. Therefore, today there is no alternative but to strengthen the embankments already built in the Brahmaputra valley. It may be mentioned that durable embankments have been built in many parts of the world where the situation may be as bad or worse. As we all know, a large part of the Netherland is located in areas with elevations below sea level. Yet they are maintaining their embankments so well that the risk of a breach is almost nil.
For this purpose, there is a need to relook at embankment design with a greater safety factor than is presently being done. It may be mentioned that many of the embankments constructed during the early period after independence don’t even conform to the present specifications and are in urgent need of structural renovation and strengthening. The use of geo-fabric materials/ clay at the core and top surface should be made a norm wherever engineering quality of soil for construction of embankment is found deficient. Depending on the quality of foundation sub-grade under the embankments, provision for cut-offs with sheet pile or clay layer below ground level may be made mandatory to avoid piping. People need to be sensitized not to weaken the embankments through activities mentioned earlier. At the same time, the district administration has to take firm measures to protect these public properties.
Accordingly, a phase-wise programme for strengthening of all existing embankments is needed to be taken up. Above all, the government has to generously fund these works as otherwise, all planning are meaningless. In this regard, it may be mentioned that Netherland, a small country, has been spending about Rs 6000 crore annually for the last 17 years in the maintenance and up-gradation of their embankments. A year’s allocation of Netherland is higher than all the money spent in embankment construction and their maintenance in Brahmaputra valley since independence. This fact speaks volumes on our Government’s spending for the protection of its citizens.
Work done so far in regard to Raising and Strengthening (RS) of embankments
Since 10th five year plan, there has been some progress towards RS of embankments in Brahmaputra valley. Under the Flood Management programme (FMP) of Government of India, 54 schemes of RS of embankments amounting to Rs 683.76 crore has been carried out so far. Out of this, 19 RS schemes were for Brahmaputra embankment and the remaining 35 RS schemes were for tributaries. The total length of 137.31 km RS works has been done in Brahmaputra embankment and 355.48 km in tributary embankments so far since starting of the 10th plan.
Besides these works, comprehensive protection work with RS of Brahmaputra embankment for a length of about 14 km was done for Dibrugarh and Palashbari town area under Asian Development Bank (ADB) funded projects. RS work was also done from under other sources of funding by Assam Government during XI and XII Plan. Overall RS work done by WRD, Assam in Brahmaputra embankment is reported to be 187 km whereas RS work in tributaries of Brahmaputra including Barak is 355.48 km during XI and XII plan period. However, these works constitute only about 10% of the total RS works required at present.
There is a need to accelerate the remaining RS works in the Brahmaputra valley and complete the same in a time-bound manner with new specification and greater safety factor. There is no point in calling our country as the 5th largest economy in the world if so many of its citizens have to suffer for lack of adequate funding for their protection.
Dhruba Jyoti Borgohain is a retired chief engineer of the Brahmaputra Board. He can be reached at: borgohain.dhrubajyoti@gmail.com