22 spots along rim of Bhakra reservoir prone to landslides: GSI

Tribune News Service

Vijay Mohan

Chandigarh, August 23

As brimming dams and risk of landslides keep the authorities and people of hilly regions on tenterhooks, the Geological Survey of India (GSI) has red flagged several factors that make certain areas along the rim of Bhakra Dam’s reservoir prone to landslides.

As many as 22 locations along the rim of the Bhakra reservoir, which has a length of around 90 km and is surrounded by mountains, have been identified by the GSI in a recently conducted survey of the area.

Findings

The major causative factors for landslides in the study area are oversaturation of debris, poor rock mass conditions and altering the natural slopes for agriculture without provisions for surface water runoff. —Report

“The major causative factors for landslides in the study area are oversaturation of debris, poor rock mass conditions and altering the natural slopes for agriculture without provisions for surface water runoff,” the GSI report states.

“Unplanned excavation of hill slopes in a few localities without proper retaining structures is another cause of slope failures in the area,” the report adds.

Landslides can be triggered by earthquakes or weather events such as cloudbursts or torrential rains. Bhakra’s reservoir is spread across the districts of Bilaspur and Una in Himachal Pradesh, which fall in seismic zones with highest vulnerability.

Though the area is not prone to major landslides, slope failures or disturbances have been observed in the area of which a few may aggravate further in case of incessant rainfall, the GSI report states.

According to officials of the Bhakra Beas Management Board, in the recent past, freak weather events that have drastically increased inflows in a very short time are being increasingly experienced. Prolonged rainfall can also cause landslides that block the flow of water in numerous rivulets and tributaries that feed the reservoir, besides increasing the influx of debris and silt in the reservoir.

According to GSI, eight per cent of the study areas around the reservoir falls in the high susceptibility category and 14 per cent in the moderate susceptibility category. High- susceptible areas are mostly observed near the left flank of the dam which is frequently disturbed by rock slides. The moderate-susceptibility areas were observed throughout the study area flanking the high-susceptibility areas.

The GSI report has recommended that the high-susceptible zones are to be avoided for any planning and construction activities. However, if at all any construction is unavoidable in these zones; detailed site specific studies must be carried out.

The left flank of the Bhakra Dam, which falls in high-susceptibility zone may be treated with appropriate strengthening and protective measures to prevent further aggravation. The right flank of the dam is a moderate landslide-susceptibility zone with a few high susceptibility patches and during extreme weather events, this zone may be a source of landslides. Activities such as excavation of slope, deforestation, construction activities by cutting of the hill slopes may be avoided in this zone, the report suggests.

The GSI has also recommended that agricultural practices in the hill slopes are to be carried out without blocking the natural drainage and domestic water discharge has to be properly channelised to prevent water percolation and oversaturation. Natural drainages, even though dry, may not be blocked or diverted as they are vital during heavy rainfall.

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