The guidelines said that in the case of projects that are “vulnerable”, the project authority or developer would be responsible for examining the upper reaches, including the reservoir, identify fault sites and take remedial measures for stabilization.

Vulnerable projects are defined as those with 400MW and above capacity.

“The examination of upper reaches may include study of hazards due to avalanche, GLOF (glacier lake outburst flood), landslide hazard analysis of slopes above the reservoir rim area, among others,” it said.

Himalayan states have witnessed several disasters floods, landslides and collapse of dams in the past few years, the latest being the collapse of the Chungthang dam in Sikkim, which followed a GLOF in northern Sikkim.

In the guidelines, CEA has outlined slope stabilization methods, practices to be followed both before construction and after commissioning of the project. It also suggested collection of records of all major slope failures including satellite imageries in and around the project area going back over 20 years.

Noting that physical access to glaciated, major landslide zones or avalanche-prone areas in the mountains is always difficult, the notification said: “Vulnerable zones in these areas can be identified using Remote Sensing and Geographic Information System (GIS) techniques with limited field work. The dimension (length, width and depth), angle and altitude of slope, volume, etc. of the potential slide zones may be measured precisely and quickly by using technologies such as drone and Light Detection and Ranging (LiDAR) technology.”

It said satellite data from the Indian Space Research Organisation (Isro) is helpful for this purpose.

It told hydropower developers to keep periodic satellite imageries in their records.

“Periodic satellite imageries shall be kept in record. The period of such images may be defined as three-six months and one such image shall be taken before construction and just before first filling of the reservoir. Suitable photography and videography of the reservoir rim area and households shall also be carried out,” it said.

Along with preparation of geological maps, geo-morphological maps, rock out-crops, overburden maps and slope classification maps, CEA has also recommended use of modern techniques such as Remote Sensing & GIS technology, drone, LiDAR technology, among others to measure and monitor vulnerable zones such as glacial lakes, landslide, and avalanche prone areas.

In January this year, the union minister for power RK Singh had directed to develop a technical manual or guidelines by CEA about aspects to be kept in view before and during construction of hydro project. Post the directive, an expert committee was constituted consisting of members from CEA, Central Water Commission, Geological Survey of India (GSI) and public sector hydro power companies for drafting the guidelines.

The norms also outlined methods for slope stabilization including geometric, hydrological and chemical & mechanical techniques.

The guidelines gain significance as Himalayan states with large number of hydro power projects including Uttarakhand, Himachal Pradesh and Sikkim witnessed severe floods, landslides, along with dam damages in the past few years.

The Teesta III hydropower project in Sikkim, collapsed last week due to a glacial lake outburst flood (GLOF), reportedly killing over 30 people. Uttarakhand has witnessed similar GLOF events and tragedies in 2013 and 2021. Both Uttarakhand and Himachal Pradesh have also witnessed floods and landslides this year leading to several deaths.

As such geological instances have gained momentum and India also has major plans to add hydro power capacity, late last month, the CEA decided to constitute a standing technical committee to study the issues in the event of any geological surprise faced in the hydroelectric projects and to examine and recommend the additional time and cost involved.

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Updated: 10 Oct 2023, 11:08 PM IST