Following the terrible disaster in Uttarakhand questions are likely to be raised once again regarding the safety and desirability of the many dams and hydel projects in the Himalayan region. What started as a natural disaster got much aggravated due to the various complications created by hydel projects and their tunnels., The workers and employees of these projects appear to have suffered heavily with several of them getting trapped in very difficult conditions.

This is certainly not the first time that this has happened .Various complexities and risks of constructing dams in the Himalayan region have been discussed in detail by many experts and increasingly concerned local people have been raising these issues as well, questioning also the benefits of these projects which are often exaggerated to get clearance for these projects.

Former Chairman of Central water Commission YK Murthy has written,”The program for the creation of a large number of manmade lakes is likely to have a profound impact on the environment of the entire (Himalayan) region.”

Among these various projects, Tehri Dam constructed in Garhwal region of Uttarakhand calls for special caution. As Murthy, who was writing before this construction was completed, wrote, “The dam at Tehri would not only be one of the highest structures of its kind in the world, but would call for tackling of complex technical problems involved in a rockfill dam of such a height for which there is very little precedence available elsewhere in the world.”

An eminent geologist Prof. K.S.Valdiya said, “The lower belt of the snow clad higher Himalayas i.e. the junction zone between the higher Himalayas and the lower Himalayas, frequently experiences natural calamities and tragedies. During the rainy season, large masses of mountains fall down due to the phenomenon of land sliding. This belt is also prone to earthquakes. These features are owing to special geological characteristics of the belt. It is sandwiched between two major thrusts. It is very necessary to carefully think about the construction of dams, reservoirs and even wide roads in this weak  belt. It would be rather dangerous to construct high dams and reservoirs in this belt. The heavy weight of a dam and pressure of its reservoir water can generate earth tremors. Even the use of dynamite should be prohibited in this belt.”

Heavy siltation of reservoirs can cause many problems. Murthy notes the deposition of silt, transported by the river waters, in the reservoirs triggers off a number of environmental problems. The sedimentation removes nutrient-rich materials which is locked up in the lacustrine substrata. The resultant changes in quality and quantum of the sediment and the flooding pattern affect agriculture and fisheries. Further owing to the deposition of silt, the downstream releases of the man-made reservoirs become free from silt. The resultant change in the pattern of sedimentation of the deltaic areas, combined with the increased impact of marine currents on the shore lands due to reduced flooding from the river, has in some cases, resulted in the erosion of coastal areas and the scouring of river beds.

In the specific context of Himalayan rivers Murthy says, ‘Many of the Himalayan rivers carry large loads of silt. The trapping of the silt in the reservoirs can result in some of the problems referred to above. These problems would require careful evaluation”.

Drawing attention to downstream changes Valdiya points out that the clear water released from reservoirs is  devoid of suspended silt and has stronger tendency to erode the stream-bed in order to satisfy its capacity for bed material. However, it is not the deepening of the bed of the main stream that matters, much rather the initiation of the new cycle of erosion which would manifest in the form of profound gullying of the terrain.

Fertile land in these hills is very limited, and submergence areas include some of the most fertile land. A lot of very good quality farmland of Garhwal was submerged when the Tehri dam project was constructed, discplacing a very large of farmers and other villagers.

Due to large scale blasting work, throwing up of rubble, traffic of heavy vehicles, diversion of water by tunnels several sources of water which are the only source of water of many villages will dry up.

The quality of flowing water changes when it is impounded. Depending on area-specific situations this has been linked to various diseases. Deterioration of the  quality of the famous water of Ganga (Bhagirathi) is a matter of serious concern.

The past experience of dam construction work in the Himalayan region, specially the construction of tunnels, reveals the possibility of several hazards and threat of accidents such as those experienced at Ramganga Project, Jaldhak Project (Darjeeling Hills) Pandoh-Baggi tunnel (Himachal) Chibro-Khodri tunnel (Uttarakhand) and Banihal tunnel (Kashmir).

Apart from the forest area (containing some rare and endangered species of plants) that have been lost a in Tehri  and other reservoirs of the region, the construction of these reservoirs will also have an adverse effect on the few remaining forests of the region in other ways as well. Drawing attention to this aspect Y.K. Mutthy writes, “The construction activities are bound to result i the colonization of areas which are at present relatively free from human activity. The colonization is likely to result in the deforestation of areas for creating the necessary space for various facilities for meeting the demands of fuel, construction materials etc.”

Regarding the impact on fish Murthy writes, “The construction of a dam across a river has a profound effect on the fisheries and their development. The free passage of migrating fish to and from their spawning grounds is disturbed owing to changes in water velocity, volume of discharge, water chemistry, temperature and turbidity. Theee is an abrupt change which the fish cannot stand. In some cases, the creation of reservoirs has led to the destruction of spawning grounds. Further, the impounding of water leads to temperature differentials. The temperature of deeper water layers gets stabilized whereas it fluctuates on the surface and head reaches. In flowing river water, there is a saturation of dissolved oxygen from the surface to the bottom. In impounded water saturation is only at the surface and it becomes deficient in the deeper regions, so that fish cannot survive.”

In the case of dams on Himalayan rivers, this controversy has a special significance. To quote Murthy , “Earthquakes are known to have accompanied the construction of a number of dams in different parts of the world. While there is no complete agreement among the geologists and seismologists on the exact cause of this seismic activity, there is a consensus that the seepage of water from the impoundments in vulnerable geological formations helps to trigger off seismic activity. The Himalayas being geologically very young and active, the effect of creating lakes on seismic activity in the region would have to e carefully studied.”

Seismicity and safety aspects are of the greatest importance.Valdiya writes, “A majority of the 200 odd hydel projects that have been built or are being constructed or planned in the southern front and the interior are located not far from the seismically and tectonically active zones of boundary thrusts characterized by strongly deformed and weakened rocks. The hundreds of transverse faults that tear the Himalayan terrain into blocks and segments are seismically more active than the boundary thrusts. Many of the rivers emerge into the plains through narrow valleys controlled by these faults. It is established that larger dams are capable of inducing and increasing seismicity of quite larger magnitudes.

The argument regarding the seismicity threat posed by locating large dams in the Himalayan region have been summarised by Prof. Vinod Gaur in the special context of TDP,           “Concern about the safety of the proposed Tehri dam arises from an apprehension that the site may be unstable as it is located within the severely deformed Himalayan belt which is the surface expression of one of the most energetic geodynamic processes active today. This mountain belt has been moulded from the northern borderland of the Indian Continental crust into a most dramatic morpho-structural feature of the globe, by persistent crumpling and stacking of its sheared continental slices to accommodate about 500 km of crystal shortening, ever since it collided with the Asian plate over 40 million years ago. The rate of acceleration of the new oceanic crust at the southern edge of the Indian plate points to a continuing covergence of at least 5 cm a year between the far ends of these two plates.

“Apparently, about half of this displacement is still being accommodated by deformation within the Himalayan belt, which is marked by prolific seismic activity. Eight major earthquakes of magnitudes 7.5 and larger, and a great many smaller ones have occurred along the Himalayan front since the great Assam earthquake of 1897 and numerous tell tale geomorphic evidences of recent rejuvenation have been reported. So the argument goes : the creation of a large reservoir in a region which may already be critically stressed, might induce rock failure, and if a dislocation should occur near the dam, the 260 meter thick sheet of water supported by it at an elevation of 550 meters above sea level, would turn into a veritable agent of widespread devastation downstream.”

These and related aspects of Himalayan dams should be kept in mind before taking an evidence based rational decision on constructing more dams in the Himalayan region. This is particularly true for those ecologically vulnerable regions where a chain of large and medium dams are being planned. Lahaul and Spiti region of Himachal Pradesh is one such region.  This region is highly vulnerable to floods, avalanches and landslides. Nearly 16 mega hydel projects are proposed for the Chenab basin in Lahaul and Pangi valley of Himachal. These are being opposed by local people because of their high risk and hazard potential and these warnings should be heard at the right time.

Bharat Dogra is a journalist and author. His recent books include Vimla and Sunderlal Bahuguna—Chipko Movement and the Struggle Against Tehri Dam Project..



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