The Wadia Institute of Himalayan Geology (WIHG) has suggested a Light Detection and Ranging (LiDAR) – a remote sensing method – to examine the surface in disaster-prone Himalayan state Uttarakhand. This has been recommended in a study report to examine the cause behind cracks that appeared across Joshimath – a tiny town en route to the Badrinath shrine.
“It is of utmost importance that LiDAR topographic mapping is done for the state. Planning of management and mitigation is convenient if bare-ground topography and the surface models are available to planners and decision makers,” said the report prepared by 10 scientists considered experts in Himalayan geology.
In January, more than 750 houses in Joshimath reported wide cracks, leading to panic and chaos. Further, cracks also appeared in the agricultural fields. Moreover, several establishments witnessed water oozing out of the ground. The Pushkar Singh Dhami government then ordered a study by expert institutes to ascertain reasons and recommend suggestions to prevent such cracks.
Scientists from Indian Institute of Remote Sensing (IIRS), Indian Institute of Technology, Roorkee (IIT-R), Wadia Institute of Himalayan Geology (WIHG), Central Ground Water Board (CGWB), Central Building Research Institute (CBRI), National Institute of Hydrology (NIH), Geological Survey of India (GSI), and National Geophysical Institute (NGI) conducted research and study and have submitted separate reports to the Uttarakhand government.
CONSTRUCTION IN SPRING WATER ZONE
Most of the reports have blamed unchecked construction over the past few years in Joshimath, particularly in the spring water zones, and loose debris for the sinking of the land.
“Construction of buildings in spring zone did cessation of spring flow. Cessation of spring flow increases the pore pressure which ultimately rendered the burst of ground water in form of spring,” mentions a report by CGWB.
The report recommends that “construction activities in spring zone area should be immediately stopped. Emergence point of the springs which are covered with any concrete material should be cleared”. It adds that “trench along with the retention wall may be constructed at different topographic level so that ground water pressure may be dissipated”.
The Geological Survey of India underlined that the majority of the ground cracks, irrespective of their orientation, are located in areas that are densely populated and loaded with multistoried buildings.
“The other areas where it is scanty or no habitation has so far not been affected by the recent event,” said the GSI report, clearly suggesting that heavy construction is one of the reasons behind the sinking of Joshimath.
HYDROPOWER PROJECT GETS CLEAN CHIT
Interestingly, there has been widespread debate on whether tunnel boring machines used in the under-construction 520-megawatt Tapovan Vishnugad Hydropower Project led to the cracks on the surface. The GSI report refuted such claims. It said 8.5 km of the 12 km-long tunnel had been excavated through drill machines and no blasting was done.
“Prima-facie the very question of any blast-induced damages attributing to the current situation is very unlikely,” the report mentions.
Besides, the Indian Institute of Remote Sensing concluded based on satellite imagery that subsidence in Joshimath may be due to the toe-cutting phenomenon, or slope instability as a result of seepage of local drainage water in the soil.