Come monsoon and Kinnaur in Himachal Pradesh has to face the wrath of the rain gods. Tragedy strikes in the form of the Pareechu river, a tributary of Sutlej in Tibet. This year, flash floods in Pareechu have already caused havoc in the northern reaches of the Sutlej valley.

Sutlej is a mighty river that originates in Tibet from Lake Mansarovar and Rakas Tal. Prior to entering India near Shipki La in Kinnaur, it travels some 320 km in Tibet. Of the 51,000 sq km of catchment area upstream of Rampur, 14,000 sq km lies in India. The hydropower potential in the Sutlej river basin is estimated at 9,000 MW, of which only 1,500 MW has been tapped so far by the Nathpa-Jhakri power project. There are plans for tapping another 1,500 MW.

A river basin with such a high potential for power generation is certainly an asset for the nation. However, the altitude, terrain conditions and geomorphology of the area warrant specialized feasibility studies for full utilization of the asset. Investigations by the Geological Survey of India show that the area is prone to quakes. The Kaurik fault, an active fault, passes through the area. The earthquakes of January 1975 and 1997 are attributed to this fault.

Danger zone

Debris at the mouths of most of the tributaries of the Sutlej indicate freak and sudden erosional episodes. Accumulation of snow in the higher reaches of the mountains and excessive rain during monsoon add to the total water content of the slope-forming material. Water acts as a lubricant and the rock mass slides down as soon as the angle of rest is disturbed. Upper Sutlej valley has such gravitational landslides and landslides generated by the earthquakes as well. Scars of landslides generated by the 1905 Kinnaur earthquake are still visible.

Geologists have observed that the upper reaches of Sutlej river were prone to cloudbursts in the pre-historic days also. Such cloudbursts are now a hazard since the load of silt carried by a river during a flash flood is doubled at such times. Last monsoon, more than 3,000 persons had to be evacuated to save them from the fury of the Sutlej.

Sit and watch

Studies carried out by the GSI with satellite imageries have revealed that a lake, 60 metres deep, was formed due to the blockade of the Pareechu river. Fortunately, the debris dam did not burst, otherwise the devastation downstream would have been colossal. RMSI, a global company for Geographical Information System solutions, postulated that in the case of a dam burst in Pareechu about half a million people downstream would be affected. Based on remote sensing data, RMSI projected that Rampur, 230 km downstream from the lake in Tibet, may be submerged under five metres of water. A similar flood in 2000 killed 70 and damaged around 100 bridges and the power plant at NJPC.

While plans are afoot to tap the power potential of these Himalayan rivers, the engineers have to keep in mind the high seismicity of the area and chances of flash floods. Development is for the people of the region. They have to be made aware of the possible natural hazards that haunt the area. Habitation should never be permitted below the highest flood level.

In this age of information technology, why is India caught napping? Despite having experienced flash floods in 1997, 2000 and a grave threat in 2004, no ?flood watch? system has been put in place in the area. It is not difficult to foresee such floods, provided we have the will to ?see? them. Not only Sutlej, but all the rivers along the international borders need to be strictly ?watched? for possible floods.