Mar 28, 2023
Mar 28, 2023
The narrow gorges of the Himalayas with snow-fed rivers cascading down at high velocity offer an ideal setting for generating hydroelectric power. Considered one of the cleanest and cost effective power generation processes, the hydroelectric project involves damming the river to make a storage structure from which a controlled discharge of water is created to run the turbines of the power house.
Though the concept sounds quite simple, however, in reality it involves a thorough study in terms of long time stability, safety and usefulness of the project. Earthquakes, avalanches and landslides are abundant in the Himalayas. The power projects in the higher Himalayas are prone to damage/devastation by avalanches. Therefore, prior to any construction activity all existing avalanches and possible ones are surveyed in detail and mapped.
This kind of study involves work in an inhospitable terrain fraught with a constant risk of burial under an avalanche. The Himalayan region holds an estimated share of 64,653 megawatts of hydroelectric power potential. In fact country's 73% demand of power can be met from the Himalayan rivers alone. The power generating potential of The rivers of Ganges system in the Himalayan regime is estimated to be 19,000 megawatts. The Indus river system also has almost a similar capacity. The risk therefore, is worth taking.
Some of the hydroelectric projects in J&K, Himachal Pradesh and Uttaranchal fall in the areas prone to avalanches. An avalanche can not only jeopardize the project, but it can lead to serious consequences of large scale destruction and even floods. Therefore, such areas need prior detailed investigations to assess the snow cover, annual increment and melting.
Ice and snow are not always hazardous, they are rather essential since majority of our large rivers are snow fed. Snow covered slopes offer ample scope for skiing and are a great tourist attraction.
Since the process of avalanches is quite complex and it is not necessary that it would occur with regularity, the hydro-electric projects in avalanche prone areas need to be designed suitably to avoid a future mishap.
C.V. Sangewar an experienced glaciologist of Geological Survey Of India carried out extensive snow cover and avalanche mapping in the above mountain states. Using his own observations and the glaciological studies carried out in the past by the GSI he described the findings in a National Snow Science Workshop.
Sangewar says that the Sind River in J&K between Sarbal in the east to Gagangir in the west flows through a wide glaciated valley between Sarbal and Shitkari and then through a narrow gorge up to Gagangir. In this thirteen kilometer long stretch as many as 39 active avalanche zones have been recognized by him and his associates.
Avalanches depend upon the snowfall, temperature, wind-speed and of course geo-morphology of the area.
During peak winters that is from December to February this area receives on an average three meters per month snow fall. The snowfall starts from November and continues till April. Monthly average snowfall data for a period from 1979 to 1982 in this area shows a peak of 270 and 240 cm in February and March respectively, with highest snowfall of 373 cm in March. Similarly the highest and the lowest temperatures in the area in the month of February vary between 4 to -15.60C. Sangewar found that maximum wind velocity is during 1300 to 1400 hours.
The avalanches of this area have been referred as 'loose' avalanche or 'slab' avalanche. The left bank of the Sind river is more avalanche prone than the right bank. During an avalanche the snow slides in this area for about 300 to 400 meters and dumps all that it carries in its wake in the river. While working out the possibilities of avalanches in such areas a prior knowledge of volume of snow/debris brought down by an avalanche and its maximum impact force on any stationery object is essential.
The maximum debris volume carried out by one of the avalanches in the Sind valley is 39208400m3. Whereas yet another avalanche though with much less volume of snow and debris has an impact force of 87.6 tonnes/metre2. Here it is worth recollecting that an impact force of 100t/m2 is capable of moving reinforced cement concrete structures.
The Dhauliganga valley in Pithoragarh district, Uttaranchal has 21 avalanches in the area between Chalkham to Dugtu. This area experiences heavy snowfall in the months of January to March. Highest snowfall recorded in January has been 220 cm. The avalanches come with such a force that some of them carrying debris cross over to the other side of the river. The debris height is 20 to 30 m and often the river is temporarily blocked.
Amongst the avalanches studied by Sangewar in Dhauliganga four major avalanches directly affect the proposed hydroelectric project stage IV. Maximum impact force of 29.3-45t/m2 has been worked out for the avalanche Sela II.
Developing hydroelectric projects in avalanche prone areas is quite a task and requires a close and careful study before execution of the project. Mountain eco-system is fragile and the present crisis of global warming has further aggravated the situation. Not only avalanches but even the bursting of glacial lakes is becoming common. Retreating glaciers leave behind thick piles of rocks, rock flour and ice. These form natural dams and are capable of holding huge volumes of water. Unfortunately these moraine dams lack the mechanical strength to retrain water for more than few decades. Water action causes erosion in the walls of such dams and seepage starts. On the other hand rapid melting of ice adds to the volume of water. Often during a heavy rainstorm, avalanche or a rockfall these dams cave in and release huge volumes of water. The flash floods become a big hazard for the power projects and habitats downstream.
In 1994 glacier lake burst in the Luana region of Bhutan flooded a number of villages and endangered thousands of lives. Dudh Kosi lake burst in Nepal in 1997 had similar repercussions. Similarly the possibilities of a lake burst in the course of Pareechu river, a tributary of Sutlej created quite a panic downstream in Indian territory. Nathpa Jhakri power project in the higher reaches of Sutluj River in Himachal Pradesh was endangered.
Most of the Himalaya lies in the territories of India, Pakistan , Nepal, Bhutan and Afghanistan. These countries are trying to cope up with the pace of development. Development of hydro-electric power projects is the priority. It is time that a complete picture of avalanches and glacial lakes is brought out.
Apart from killing people, burying habitats, damaging power projects, the avalanches are the worst enemies of forests and grasslands. Trees in the path of an avalanche are thrown uprooted and tossed around like match sticks. Grasslands become bald in the wake of an avalanche.
Being a natural hazard they can not be wished away. It is for the people to avoid the paths of avalanches and remain safe.
Landslides are yet another mass wasting process that cause severe damage to infrastructure and endanger the human lives. We shall read about them in the forthcoming issues.
More by : V. K. Joshi (Bijji)