Ground Subsidence Around Joshimath ..जोशीमठ के आसपास भू-धंसाव

–By Piyoosh Rautela–

एक सप्ताह से अधिक समय के बाद भी लगभग 400 – 500 एलपीएम पर निरंतर प्रवाह किसी प्रमुख भूमिगत जलाशय के टूटने का संकेत देता है। जिस दबाव से पानी बह रहा है, वह बताता है कि जलभृत का स्थान नदी के तल से काफी अधिक ऊंचाई पर होना चाहिए; शायद जोशीमठ के आसपास या उससे भी ऊपर। पानी का मैलापन उस मलबे के द्रव्यमान के क्षरण का संकेत है जिस पर जोशीमठ स्थित है। जैसा कि अपेक्षित है, मलबे की सामग्री के इस क्षरण के परिणामस्वरूप जमीन का धंसाव होता है जो घरों और अन्य संरचनाओं में दरारों में परिलक्षित होता है। लगातार धंसती जमीन के कारण कई घर जर्जर हो गए हैं और बड़ी संख्या में परिवारों को वैकल्पिक सुरक्षित स्थानों पर स्थानांतरित कर दिया गया है। जनता के बीच भय, आशंका और दहशत है, जैसा कि स्वाभाविक है और राज्य मशीनरी ने घटना के कारणों का पता लगाने और उपचारात्मक उपायों का सुझाव देने के लिए देश भर के विभिन्न वैज्ञानिक और शैक्षणिक संस्थानों से टीमों को जुटाया है। साथ ही राज्य राहत और पुनर्वास के उपाय कर रहा है।

Habitations have come into existence, primarily as a consequence of the basic human urge to socialize and stay together, perhaps for safety and security, more than anything else. It is around these settlements that humans started various livelihood chores including agriculture, hunting, and gathering.

Settlements in the hills

Agriculture being the primary economic activity in the hills, human settlements in the hills started around places that had rich and fertile soil cover. Except for alluvial terraces, soil formation in the mountains is facilitated largely by landslides, and therefore it is no surprise that most human habitations in the hills are located in close proximity of old stabilized landslides.

The knowledge accumulated over generations through observation and experience sharing made indigenous people of the region realize the precarious nature of these deposits and therefore, despite developing the stabilised landslides for agriculture by constructing terraces, they did not settle down over these.

The human habitation was therefore invariable sited at some distance from the agricultural fields, generally at a higher ground and over firm and stable rocks which provided safety from both floods and landslides.

The habitations in the hills were thus located over higher ground despite agriculture and water both being on middle and lower slopes. Rather than jeopardizing safety and security of the community, the indigenous people thus knowingly accepted the challenge of negotiating some distance on a routine basis for both fetching water and carrying out routine agricultural chores. This clearly shows that unlike us, these people gave preference to safety over comfort.

Growth of urban centers

With the passage of time, the growth of secondary economic activities resulted in urban growth around settlements disposed of with some advantages.

Pilgrimage has always been a major economic activity in the Garhwal Himalayas as large number of people from across the country came here to visit Badrinath, Kedarnath, Gangotri, and Yamunotri. The settlements en route to these pilgrim centers with geographical and strategic advantages thus developed as halting places for the pilgrims and urban growth took place around these.

Joshimath issue

The growth of Joshimath which is located en route to Badrinath can be understood in this background. As are most other habitations of the region, Joshimath is also located over old stabilized landslide material and large boulders of gneisses scattered around the area in sandy–silty matrix provide conclusive evidence for saying so. The size of these boulders is enough to imagine the enormity of this mass movement and it is highly likely that some major seismic shaking in the past resulted in this landslide.

This landslide is however not certainly associated with the 1 September 1803 Garhwal Earthquake that is the last major earthquake to hit this region and we hardly know anything about previous earthquakes in this region.  Thus nothing can really be said about the triggering mechanism of this landslide.

As regards, landslide, in situ rocks are nowhere exposed in and around Joshimath and Auli. Therefore one can only extrapolate the ones exposed along the left bank of Alaknanda and conclude that in situ rocks around this place are located deep beneath the cover of landslide debris. These rocks are at the same time not disposed favorably and the city is located over rocks dipping north in the direction of slope. The geological disposition of the place thus makes it poised for instability.

Ground subsidence around Joshimath

Geological disposition and the presence of a thick pile of debris make this place unsuitable for bearing the load of buildings and other structures that have been constructed here. This load actually makes the place more susceptible to slope instability.

The people of the region understood the relationship between groundwater infiltration and slope instability and therefore managed Jungle Guls to the upslope of identified slide-prone areas, so as to ensure safe disposal of excess rainwater into the nearby water channel. The growth around Joshimath was highly unplanned nobody took care of water disposal, both rainwater, and household wastewater.

All this water saturates the old slide material, and in the process leaches out soluble materials and fines; piping of fines that expresses itself in differential ground subsidence being observed since 1976 as is put forth by the report of Mishra Committee.

Subsidence aggravated

As suggested by the people, the pace of ground subsidence has been enhanced after severe toe erosion by the floodwaters of Alaknanda river in the aftermath of the 7 February 2021 Dhauliganga floods.

It is on the night of 2 January 2023 water started to gush out of the hill slope around Marwari in the campus of the JP Colony on the left bank of Alaknanda, to the downslope of Joshimath. The water is highly charged with silt and clay and is gushing out under high pressure.

The observations

Continuous flow at around 400 – 500 lpm even after more than a week suggests a breach of some major underground reservoir. The pressure with which the water is pouring out suggests that the location of the aquifer to be at a significantly higher elevation from the river bed; maybe around Joshimath or even higher. The turbidity of the water is indicative of the erosion of the debris mass on which Joshimath is located. As is expected this erosion of the debris material is resulting in ground subsidence that is reflected in cracks in the houses and other structures.

A number of houses have become depilated due to the continuously subsiding ground and a large number of families have been shifted to alternative safe locations. There is fear, apprehension, and panic, as is natural, amongst the masses and state machinery has mobilized teams from various scientific and academic institutions across the country to establish the cause of the incidence and suggest remedial measures. The state is at the same time undertaking measures for relief and rehabilitation.

Future scenario and actions

The pace of ground subsidence is to ameliorate only after the breach of the aquifer is plugged or the aquifer drains out completely. The extent of the aquifer not yet ascertained former seems a remote possibility but sooner or later the aquifer is to drain out.

By the time ground subsidence ameliorates the dilapidated structures in the affected area have to be dismantled and the load over the slope has to be minimized and the people in affected area have to be rehabilitated. It is good to see that the state government has already put in place teams for undertaking this together with assessment of bearing capacity and accordingly regulating developmental initiatives in the area.

Moreover, it is required that adequate measures are taken to ensure that the distress does not extend in future to the hitherto not severely affected area of Joshimath. State has already initiated action for preparing a comprehensive drainage and sewerage plan for Joshimath.

As has been brought out by various committees the state has also initiated action for putting in place measures along the left bank of Alaknanda to arrest erosion.

Way forward

Having said and discussed the habitation pattern in the region together with problems around Joshimath, it needs to be emphasized that Joshimath is the warning sign or tip of the iceberg. A number of urban centers of this region are faced with similar situations and if measures are adequate curative and mitigative measures are required to be taken on war footing to ensure that Uttarakhand does not witness more Joshimath-like situations in near future. Thankfully so, the state government has initiated action on these lines involving most academic and research institutions under the guidance of the National Disaster Management Authority and Ministry of Home Affairs which are closely monitoring the situation. The seriousness of the issue is evident from the visit of all the members of NDMA to the affected area together with the Secretary, Border Management and Joint Secretary, Disaster Management as also Secretary, Disaster Management, Uttarakhand Dr. Ranjit Sinha.

It would however be required that strict compliance with the norms as also recommendations of various committees and institutions is adhered to, and for that more than anything else continuous dialogue with the affected community would be required.

 

(The post Ground subsidence around Joshimath appeared first on Risk Prevention Mitigation and Management Forum.)