Dec 02, 2023
Dec 02, 2023
This year’s premature, yet powerful rainfall of June caused havoc in Uttarakhand. Thousands perished and still the news of more dead is trickling down. The worst sufferers were the local residents, who lost their livelihood, breadwinners, houses and belongings. Those involved in tourist trade and escaped the wrath of the nature are now jittery of going back to work. Why it happened so suddenly, is a question that often haunts the minds.
|The surface of the mountain slopes is attacked by various natural agencies, which trigger weathering. Normally the vegetation on the surface binds and holds the lose material from slipping down. But in the event of a cutting/erosion at the toe of the slope or in between due to road construction activity and or other construction activities, the stability of the mountain slope is disturbed.|
After declaration of the statehood, Uttarakhand launched an aggressive marketing of tourism. No harm in that, because the state has a potential for developing tourism, while there is very limited scope for industry or agriculture. Yes after tourism, the other possible paying venture is the horticulture.
Tourism means, more roads, more comforts for the people to stay. In other words lot more excavations for road construction and hotels etc. The population boom on the other hand has certainly affected Uttarakhand. More people mean more houses. As the towns in the newly formed state became congested, people started looking for plots elsewhere-on the outskirts of towns, in the valleys on the terraces close to the rivers and even slopes were not spared, where houses came up on RCC pillars presumably sunk deep in the bed rock!
Here comes the spanner in the works. Let us forget the past and recall just what happened in 2010-There was a sudden heavy rainfall on September 18 and 19, in the Ganga watershed associated with regional monsoon event that occurred between Mynamar and Middle East, says Subrat Sharma of GB Pant Institute of Himalayan Environment and Development (GBPHIED), Kosi, Katarmal, Almora.
It is pertinent to understand the change in the pattern of rainfall in the recent years. Cloud bursts or sudden heavy rainfall often occurs at night. Apart from damage to the houses, water gushing down the hill makes the turbulent Himalayan streams and rivers swell. In addition, lot of water infiltrates the surface of the slope. This infiltration is one of the major causes of slope failures in Himalayas.
Recently Subrat Sharma studied the relationship between heavy rainfall and slope failures and published his findings in Current Science. Rain water as it infiltrates the ground and gushes down the hill often forms subsurface channels. The surface of the mountain slopes is attacked by various natural agencies, which trigger weathering. Normally the vegetation on the surface binds and holds the lose material from slipping down. But in the event of a cutting/erosion at the toe of the slope or in between due to road construction activity and or other construction activities, the stability of the mountain slope is disturbed. Over and above, the water filled channels underneath become a source of lubrication for the land mass which is already in a disturbed state. Consequently, the whole mass of rocks and mud begin to move down the hill, leaving a trail of destruction.
At times the subsurface channel of water gets obstructed and water comes out at the first opportunity. During the excessive rainfall of September-October 2010, the‘Goth’ or the room at the basement used as a cattle shed in the village houses on the mountain slopes were flooded, while the rooms above were affected by seepage of water. The landslides generated due to heavy rain, especially due to downwards movement of infiltrated water also carried with them the terraced fields with standing crops. Thus the poor villagers had to face double the loss-that is the loss of houses and also the loss of the crops and precious agricultural land.
A landslide spares no one in its wake. Roads, footpaths leading to the villages and also the connecting arteries of roads all were washed away. About 20 km length of the National Highway 87 was washed away in Nainital district. The flooding of rivers in the Himalayas ultimately caused floods in the plains and areas close to the foot hills of Punjab, Himachal Pradesh and Uttar Pradesh were the worst affected. Delhi-Bareilly-Lucknow highway, NH24 remained blocked for several days.
In order to work out the relationship of heavy rainfall and landslides, Subrat used data from the three weather stations, at, viz. GBPHIED, Aryabhatta Research Institute of Observational Sciences (ARIES) Nainital and Government Inter College, Dwarahat. It was noticed that during the period between 15-19 September, 2010 rainfalls varied from 215.8 to 711 mm. The astonishing part was that out of the total rainfall, 64% occurred on 18thSeptember.
The colossal floods created by this rain could not have been due to a local cloud burst, suspected Subrat. Thus he studied the satellite imageries of ‘GeoEye’ satellite Kalpana-1. He had rightly guessed. It was seen that a jet stream of dense clouds migrated over the Himalayas from east to west between the night of 17 and 19 September. The clouds moved swiftly between Thailand, China and Mynamar and Uttarakhand, traversing a distance of about 1950 km in about one and half hours. The density of cloud cover was highest over Uttarakhand and eastern Himachal Pradesh. This was the area worst affected.
While concluding he says that that it is confirmed that the catastrophe occurred due to a regional event that stayed prolonged over Ganga watershed in the Indian Central Himalaya.
Depending upon the saturation of the soil and subsurface and also other characters of the slope, landslides of different magnitude are generated. Often a small landslide may become a roaring mass of mountain hurtling down because of favourable conditions.
Thus while developing Uttarakhand, the government and the people must pay adequate attention to the drainage of water, so that damage due to lubrication by water is minimised. Studies conducted in the eastern Himalayas and Nepal have shown that the slope gets destabilised if the rainfall is above a threshold value ranging from 196.2 to 200 mm within 22 hours to four days. However, it is also a fact that areas where adequate drainage had been developed in the past remained comparatively stable.
Detailed studies are required in Uttarakhand to work out the threshold values of rainfall versus slope failure. Forewarning is always better as a means of pre-disaster mitigation. For which, a Unified Processing Centre UPC) linked with Earth Observation satellites, many more unmanned automatic weather stations, sharing of information by other organisations via fast communication links have been recommended by Subrat. The UPC could be linked with the offices of the District Magistrates all over Uttarakhand, so that precautionary steps could be taken before the disaster struck.
In a nutshell a real time early warning system for landslides is the need of the hour. We can afford to send satellites in the space; we can afford to develop excellent communication networks. There is no reason that we should lag behind in developing this early warning system so that lives are not lost due to bureaucratic rigmaroles.
More by : V. K. Joshi (Bijji)