Scientific and technical institutions investigating land subsidence in Joshimath have identified several contributing factors to the crisis. These include the town's precarious location on a slope with loose sedimentary foundations, population growth, the construction of multi-story buildings, and the absence of an adequate water disposal system for runoff from higher elevations.
Although these reports vary in their approaches, they largely concur on the combination of factors exacerbating the situation in Joshimath earlier this year. The town's vulnerability to land subsidence, primarily due to its foundation of loose sediments, has been accentuated by the increasing population density and the construction of multi-story structures, including hotels. These factors are consistently cited across reports submitted by eight different institutions.
In response to the crisis in January of this year, several institutions, including the Central Building Research Institute, Central Ground Water Board, Geological Survey of India, Indian Institute of Remote Sensing, Indian Institute of Technology-Roorkee, National Institute of Hydrology, National Geophysical Research Institute, and Wadia Institute of Himalayan Geology, were tasked with studying the issue.
Despite the completion of these reports by the end of January 2023, they were not made public until the Uttarakhand High Court intervened, questioning the rationale for withholding them. Following the court's directive, the Uttarakhand State Disaster Management Authority released the reports on its official website. These reports collectively comprise more than 700 pages.
In January of this year, Joshimath experienced the appearance of cracks and fissures on houses and the ground, causing alarm. Consequently, authorities evacuated a significant number of residents, particularly from the severely affected Sunil, Singdhar, and Marwari wards, to temporary relief centers.
"A temporary storage was created due to blockage of sub-surface channels which eventually burst from the weak point of strata when the hydrostatic pressure of stored water exceeded the soil-water bearing capacity of the area," the NIH report said.
"Safe disposal of water coming from the upper reaches and waste of town should be the top priority," the NIH said in one of its recommendations.
The Central Ground Water Board has proposed a solution to address the issue. They suggest constructing trenches along with a retaining wall at various topographic levels to dissipate groundwater pressure effectively, thus preventing future cracks. Additionally, they recommend an immediate halt to construction activities in the spring zone area.
The Indian Institute of Remote Sensing said, "Subsidence in this region may be due to the toe-cutting phenomenon, slope instability as a result of seepage of local drainage water in the soil, terrain and edaphic characteristics, loose and unconsolidated moraine materials of the slope (due to old landslide) and flash flood events in and around the area in the recent past."
"This has resulted in the development of cracks in the ground as well as houses in Joshimath...," it said.
The Geological Survey of India (GSI) strongly advises implementing ground-based terrestrial-monitoring in various areas of Joshimath.
"The main reason for the subsidence appears to be internal erosion caused by the subsurface drainage, which may be due to infiltration of rainwater/melting of ice/wastewater discharge from households and hotels. Though subsidence is a continuous phenomenon, it can be minimized by controlling infiltration of water, which helps in minimizing internal erosion," the IIT-Roorkee said in its report.
Image source: Economic Times