Morainic foundation, population, building pressure behind Joshimath subsidence: scientific reports

Scientific and technical institutions studying land subsidence in Joshimath have attributed the crisis to the hill town's location on a slope over morainic deposits or loose sediments, population pressure, construction of multi-storeyed buildings and the absence of a system for proper disposal of water coming from the upper reaches.

Though the reports are separate and approach the problem from different angles, they are largely in concurrence with each other on the combination of factors that may have led to the aggravation of the situation in Joshimath early this year.

Joshimath's susceptibility to land subsidence because of being located on a foundation of loose sediments coupled with increasing population pressure and multi-storeyed buildings, including hotels, in the town are some of the factors cited in nearly all the reports submitted by eight different institutions.

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 engaged to conduct a study of the problem when it was at its worst in January this year.

The institutions submitted their separate reports to the National Disaster Management Authority by the end of January 2023 but they were not made public until the Uttarakhand High Court intervened, questioning the justification for not releasing them.

The Uttarakhand State Disaster Management Authority made the reports public by uploading them on its official website on Sunday following the high court's intervention.

Hearing a PIL recently, it had questioned the justification for not making the reports public. Put together, the reports run into more than 700 pages.

Cracks and fissures had appeared on houses and on the ground in Joshimath in January this year causing concern which led the authorities to evacuate a large number of people, especially those living in the worst-hit Sunil, Singdhar and Marwari wards of the town, to temporary relief centres.

"There is a need for reviewing the principles of town planning for development of towns in hilly regions with rigorous stress on good construction typology, practices, material, regulatory mechanism, and awareness among the stakeholders based on geo-technical and geo-climatic condition," the CBRI said in its recommendation.

The recommendation was based on extensive physical damage assessment survey of 2,364 buildings, spread over 2.8 sqm hilly terrain, in nine administrative zones in Joshimath, it said.

Joshimath town is situated on Vaikrita groups of rocks overlain by morainic deposits composed of irregular boulders and clay of varying thicknesses which are less cohesive and susceptible to slow subsidence and landslide subsidence, the Central Building Research Institute (CBRI) said.

The National Institute of Hydrology (NIH), which studied the water seepage point in Jaypee colony area of Joshimath from where water kept flowing with great force for days causing concern among authorities, said it was an eruption caused by blockage of sub-surface channels.

"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 top priority," the NIH said in one of its recommendations.

The Central Ground Water Board suggested that trenches along with the retention wall may be constructed at different topographic levels so that ground water pressure may be dissipated and cracks do not appear in future.

It also recommended that construction activities in spring zone area should be immediately stopped.

The Indian Institute of Remote Sensing said, "Subsidence in this region may be due to 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 development of cracks in the ground as well as houses in Joshimath...," it said.

The GSI said it is strongly advised to carry out ground-based terrestrial monitoring in different parts 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/waste water discharge from household 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.