Indian officials and administrators continue to plan ineffective flood-protection interventions along the Kosi, even though there is a straightforward solution.
To date, flood-control mechanisms in India have been almost completely guided by the colonial legacy of embanking rivers, as well as by the simplistic engineering approach of dam-building. The enduring myth that freedom from floods can ever actually be achieved demonstrates a dramatic lack of understanding of how river basins function. In contrast, farmers in Assam, Bihar and Bengal had an age-old culture of living with floods. Indeed, they welcomed low-intensity flooding, having inherited a uniquely evolved technique of replenishing their farmland with layers of fertilising silt carried by the water, a method called ‘overflow irrigation’.
Despite having functioned well for centuries, such traditions began to disappear during the British Raj. At that point, many rivers in Bengal were embanked in an attempt to combat the annual flooding – including the Damodar, often called the ‘sorrow of Bengal’ due to its frequent flooding. These bunds did ensure security against low-intensity flooding, but the long-term effects were detrimental, leading to the decay of river systems and the congestion of drainages. As recurrent breaches of the embankments and drainage congestion became commonplace, the sense of security provided by the bunds proved to be false. By 1858, the decision was made to demolish the right embankment on the Damodar, in order to ensure the safety of the left bank, through which the Grand Trunk Road and the railway were aligned. The so-called Sepoy Mutiny of 1857 probably contributed to this decision, making the British feel that railways and roads needed to be secured from floods in order that troops could quickly be deployed to areas of revolt. The whole experience was to be an eye-opener for the British engineers, who did not repeat their mistake by trying to tame the Kosi.
North Bihar is the proverbial land of rivers, with the Kosi often described as the most notorious of all. This dubious fame is intertwined with the river basin’s ‘fluvial geomorphology’, or how the river’s flow has shaped the terrain of the watershed. Here, too, farmers had long understood that the floods were, in many ways, blessings in disguise. But the first human intervention into the lower Kosi basin introduced an alien development model, as it was instituted by the British. During the mid-18th century, a road- and rail-focused urban/industrial model of development was imposed onto an inappropriate geographical setting, leading to a spectrum of detrimental environmental changes. The roads and railways were outfitted with inadequate culverts, which inevitably intercepted crucial drainage points. In turn, this led to an expansion of floodable areas, outbreaks of malaria from mosquitoes that bred in the stagnant water, and a general decline in crop production in the impacted lands. Here was yet another instance of humanity’s ineffectual, and perhaps disastrous, meddling with hydro forces larger than itself.
The Raj ended in 1947. But the focus on purely Western-style hydraulic engineering solutions survived, used to augment lean-season flows, combat flooding, resuscitate the navigational channel and ensure adequate irrigation. These attempted solutions continued to imperil the ecological security and delicate hydrological balance of the densely populated Gangetic plain. Over the course of the past six decades, this has led to the loss of livelihoods for many poor, rural families. In West Bengal, official documents state that erosion has increased since the Farakka Barrage was completed in 1975, rendering homeless at least a half-million people.
The vast and intricate mesh of channels in the lower Kosi basin are characterised by a number of unique features, of both the water flow and the surrounding geology. One such trait is the gradual westward shift of the Kosi due to ‘secular oscillation’, or the river’s migration controlled by tectonic tilt. This has subsequently given rise to certain processes that have become typical of the basin. For instance, as the Kosi has taken a longer downward path, the slope has declined, resulting in slower velocity, increased sedimentation and widening of the riverbed. This has, of course, taken place over a very long period of time. Given this lengthy timeframe, over the past half-century the basin has experienced significant difficulties in adjusting to the combination of accelerated natural and manmade changes to the Kosi’s flow. As a result, myriad severe problems have emerged, both ecological and human.
Following the Raj-era construction of railways and roads that constricted drainage, the second phase of engineering intervention in the lower Kosi basin took place from 1955 to 1959. At this time, the river was partially embanked, again with the objective of flood control. Suddenly, over a million people from 380 villages were trapped between the embankments, while more than three million people living outside the bunds were initially thought to be assured of safety from flood waters (See Himal Dec 2008, “Finger in the dike”). This protection, however, proved to be a myth, as recurrent breaches in the embankments became commonplace.
Even with the clear failure of the engineering intervention undertaken during the first two phases, a third such project was begun. In March 1963, the construction of a massive barrage across the Kosi at Bhimnagar on the India-Nepal border was completed, with the twin objectives of ensuring irrigation and preventing floods. The barrage, along with an intricate network of canals, introduced an altered hydraulic system to irrigate 710,000 hectares of land along the eastern bank of the Kosi. The incomplete western canal is supposed to irrigate another 330,000 hectares of land – though, nearly a half-century on, it shows no signs of being completed.
The barrage-and-canal system resulted in two major changes in the hydraulic regime of the lower Kosi basin. First, the rate of sedimentation upstream of the barrage increased significantly. The riverbed between the bunds rose relentlessly, as it did between the embankments downstream from the barrage. As a consequence, the rate of sedimentation in the riverbed surpassed the effect of the westward sinking and tectonic tilting. There is no data available relating to the annual rate of this sinking and sedimentation, but there is no doubt that the riverbed within the embankment continues to rise due to accelerated sedimentation. Second, due to the eastward alignment of the main irrigation canal emerging from the Kosi Barrage, a complex network of 15 distributaries of the Kosi was ‘beheaded’ from the parent river – thus sealing the possibility of floodwaters spilling over into these channels. Since the floodwater and the sediment load were forced into a single channel, the dynamic equilibrium of the river basin was inevitably impaired. This led to the ‘decay’ of the western channel on which the river has been forced to flow since the barrage was built, as well as to recurrent breaches in the embankments.
In the absence of a firm scientific understanding of the geomorphologic processes at work in the Kosi delta, the flooding in this area continues to be labelled a ‘disaster’, one that needs to be ‘controlled’ by structural measures. What needs to be understood is that, with 80 percent of the annual flow coming during the monsoon months, the discharge in the Himalayan rivers are temporally skewed, and cannot be accommodated within the shallow cross-sectional areas of the riverbed in the plains. When the river enters the plains, the slope suddenly declines, causing the sediment load to be dropped on the bed, making it shallow and wide. The artificial reduction of the cross-sectional area only causes increasing vulnerability. Politicians, still guided by the old, flawed logic that the flood can be controlled by structural measures, steadfastly deny the lessons of the past: that no engineering marvel can keep the Kosi’s massive discharge within the shallow areas between the manmade embankments. One way or another, the silt-laden floodwaters have to be allowed to spill out.
The only sustainable option for the Kosi challenge, added to by the breach of the embankment above the barrage in August last year, is to divert these floodwaters waters into convenient outlets. The decision to plug the Kusaha breach (which caused the flood in August 2008) and push the Kosi back to its western channel only paves the way for yet another disaster in the future (and another after that), as the channel is no longer in equilibrium. The only technical solution seems to be to channel the floodwaters through the old courses. Such an undertaking would need some engineering intervention in order to connect the ‘beheaded’ distributaries with the eastern canal (see map), as well as to establish flow regulators at the off-take points, the proposed points of connection between the old channels and the main canal. The selective dredging of some stretches of the old channels would render quick outlets for floodwater.
The benefits from such a project are there for all to see. Utilising the old channels would be less expensive and provide a more realistic solution to the recurrent ‘disasters’. This option would also manage the floods better than would the proposed high dam in Nepal. Sadly, there is no sign that Indian officials involved in intervention with river systems will move away from simplistic engineering to less intrusive, more effective methods of management. Water managers in India continue to deny the holistic eco-hydrology of the river basin, and instead try to solve the problem from a narrow, sector-based outlook.
~ Kalyan Rudra is a former member of the National Flood Management Core Group of India.
Romila Thapar addresses invitees at the
Southasian relaunch of Himal Southasian,
IIC, New Delhi, January 2013.
Flickr / girl.from.melbourne
An early monsoon
On June 16 2013, the India Meteorological Department confirmed the early arrival of monsoon rains across the whole of India. Full coverage was not expected until the middle of July, making farmers hopeful for a bumper crop.
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Venu Madhav Govindu notes the 'fundamental importance' of a good monsoon for both city and rural dwellers. (August 2003)