Unplanned infrastructure development, inadequate drainage and excavation of roads through unstable debris slopes accelerated the instability and land subsidence in the historical Himalayan town of Joshimath in Uttarakhand. These are the findings in the study ‘Unstable slopes and threatened livelihoods of the historical Joshimath town, Uttarakhand Himalaya, India’, published in the latest edition of Current Science journal.
The study was conducted by Indian geologists and scientists between August 2022 and January 2023 when the region reported land subsidence resulting in the evacuation of the locals from their houses. SP Sati, a senior geologist and head of department of basic and social science, College of Forestary, Ranichauri said, “As an immediate measure, there should not be any excavation activities, particularly of the precariously balanced crystalline boulders. The landslide deposits contain moderately fine grains (pebbly sand), which act as the filling material between the boulders.
“It has been observed that there are cavities (mimicking potholes) on the surface which we speculate are caused due to the selective removal of fine sediments by unregulated domestic wastewater drainage. In recent times, these cavities are posing a serious threat to the stability of the built-up structures in Joshimath town.”
Authors Maria Asim and Shubhra Sharma from Department of Geography, Institute of Science, Banaras Hindu University were of the views that since the roads at various zones in the region were undergoing subsidence at multiple places, special engineering skills is required while excavating the slopes for road construction, which are currently lacking. “Consequently, our response to maintaining the roads in such areas is reactive (repair following subsidence) and not proactive (providing long-term slope stability).”
One of the ways to circumvent this chronic problem of continuous creeping and subsidence is by making elevated corridors with pillars deeply anchored on hard rock substratum, as done for the ropeway in Joshimath town, they said.
The other authors of the study include, YP Sundriyal from Department of Geology, HNB Garhwal University, Srinagar , Naresh Rana from the Department of Geology, Centre for Advance Studies, University of Delhi and Vijay Bahuguna who works with Department of History, VSKC, Govt PG College in Dehradun. Shubhra Sharma is currently in the Geosciences Division, Physical Research Laboratory, Ahmedabad.
The fragile town, in the last few decades witnessed significant surge in population resulting into huge infrastructure development. Thus causing immense pressure on the finite resources and limited accommodation space on precariously balanced vulnerable slopes.
For example, multi-storied houses in the Yamuna and Bhagirathi valleys are hundreds of years old and have withstood several earthquakes, including the 1991 Uttarkashi and 1999 Chamoli events, said the study.
Similarly, the traditional irrigation system in the hills is based on small canal networks which are diverted from small to moderate streams without obstructing them. This type of irrigation is still in practice.
However, in the last few decades, Uttarakhand Himalaya has witnessed large-scale infrastructural developmental activities, particularly the proliferation of urban towns driven by the increase in urban population up to 20 times between 1901 and 2011.Such a rapid rate of urbanization, if executed in an unplanned manner, is likely to create an additional burden on existing resources and infrastructure, adversely impacting the mountain ecology and terrain instability.
Therefore, it is important to assess the emerging risks and vulnerabilities associated with growth of infrastructure on precariously stabilised slopes, particularly in the Higher Himalaya, said the authors.
