Eight institutes give an array of reasons for Joshimath sinking

Eight institutes give an array of reasons for Joshimath sinking

Subject: Geography

Section: Physical geography

Context:

• Separate studies conducted by eight premier institutions of India to know the cause of land subsidence in Joshimath town of Uttarakhand attributed seismic activities, construction loopholes, population pressure, poor drainage system and others as the ‘likely’ reason for the sinking of the Himalayan town.

Joshimath:

• Joshimath town is situated on Vaikrita groups of rocks overlain by morainic deposits which are composed of irregular boulders and clay of varying thicknesses. Such deposits are less cohesive and susceptible to slow subsidence and landslide subsidence.
• With every study conducted with a different approach, these reports reaffirmed the sensitivity of the area but nothing concrete has come out on what exactly went wrong in January.
• Studies conducted by:
  • The Wadia Institute of Himalayan Geology (WIHG), the National Geophysical Research Institute (NGRI), the National Institute of Hydrology (NIH), the Indian Institute of Technology (IIT), Roorkee, the Indian Institute of Remote Sensing (IIRS), the Geological Survey of India (GSI), the Central Ground Water Board (CGWB) and the Central Building Research Institute (CBRI).

Findings by the eight institutions:

• CBRI report:
  • The CBRI stated that Joshimath town has 44%, 42%, 14% of masonry, RCC and other (traditional, hybrid) construction typologies, respectively, among which 99% are non-engineered. It means they are not in compliance with the National Building Code of India, 2016.
• The NIH report said that maps of various springs, drainage networks and areas of subsidence infer that land subsidence and subsurface water in Joshimath might have some connections.
• The report also highlighted that the gush water is fresh water and not contaminated by the local drains, thus NTPC was not responsible for the joshimath sinking.
• The WIHG mentioned earthquakes as a reason for slow and gradual land subsidence.
• IIT Roorkee report: 
  • 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 household and hotels. Though subsidence is continuous phenomenon, it can be minimised by controlling infiltration of water, which helps in minimising the internal erosion.
• ISRO report:
  • After an analysis by the Small BAseline Subset Interferometry SAR Technique it said that, the subsidence in the Joshimath 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 town.
• The analysis of almost each report matches with the recommendations and precautions recommended in the M.C. Mishra Committee report.

Source: TH