The Subansiri Lower Hydroelectric project (SLHEP) located on the Assam-Arunachal border has recently made news headlines when it was affected by a landslide during pre-monsoon rain. Incredibly, the project survived unscathed and is still on track to become operational by June 2023.
Understanding Landslides
A landslide is characterized as the movement of a mass of rock, debris, or earth down a slope. The term incorporates five types of slope movement: falls, topples, slides, spreads, and flows. The primary causes of landslides are rooted in geology, morphology, natural occurrences, and human activities.
Geology relates to the characteristics of the material involved in the landslide. For example, the earth or rock might be weak or fractured, or different layers may have different strengths and levels of rigidity. Morphology denotes the structure of the land; slopes that lose their vegetation due to fire or drought are more susceptible to landslides.
Natural causes could include heavy rainfall, earthquakes, and snowmelting, along with undercutting of slopes due to flooding. Human activities like agriculture and construction can also contribute to increasing the risk of landslides.
Landslide-Prone Areas in India
Landslides are a common occurrence in the entire Himalayan tract. Around 66.5% of landslides are reported from the North-western Himalayas, and approximately 18.8% from the Northeastern Himalayas. Other landslide-prone areas include the Western Ghats (about 14%) and Konkan regions as well as Nilgiris in Tamil Nadu.
Insight into the Subansiri Lower Hydroelectric Project
The SLHEP is an under-construction gravity dam (nearly 90% completion) with a capacity of generating 2000 MW (8×250 MW) power. It holds the record as the largest hydroelectric project conceived in India thus far and is a run of river scheme on river Subansiri.
The construction of the SLHEP is being undertaken by the National Hydroelectric Power Corporation (NHPC) Limited. Subansiri, also known as the “Gold River,” is the largest tributary of the Upper Brahmaputra river. Originating from the Tibetan Himalayas, the river flows into India via the Miri Hills in Arunachal Pradesh.
Controversy Surrounding the SLHEP
Despite its potential, the SLHEP has been inundated with controversy and local agitation over several dam safety and administrative issues involved in the project’s implementation. The main bone of contention is that the project contravenes the 1980 Brahmaputra Board Act by transferring the work of the Water Resources Department of the Subansiri Basin from the Brahmaputra Board to the public and private sector.
There are also concerns about increased seismic threat levels to the dam, as pointed out by the Indian Institute of Technology (IIT) Roorkee. Despite these controversies, it’s worth noting that Arunachal Pradesh is considered the powerhouse of the country, housing 34% (50,328 megawatts) of India’s 148,701 MW hydropower potential.
What is a Gravity Dam?
A gravity dam is a dam constructed from concrete or cement (unlike mud and masonry stones used in embankments). The dam is designed to hold back water by primarily utilizing the weight of the material alone to resist the horizontal pressure of water pushing against it.