By Feroze Varun Gandhi
On Dec 24, 2009, a tunnel boring machine drilling into the mountain on which Joshimath resides punctured an aquifer ~3km away from Selang village – this resulted in water being discharged at ~700-800 litres per second (enough to sustain the needs of 20-30 lakh people per day) (Upadhyay, Kavita, Jan 2023). Soon after, groundwater sources in Joshimath started drying up – over time, the discharge reduced but never stopped. Meanwhile, Joshimath, built on a mountain slope with deposits from a landslide, has no system to manage wastewater. Instead, most buildings use a soak-pit mechanism, which leads to sewage entering the ground and potentially exacerbating land sinking. In addition, ongoing infrastructure projects (e.g. the Tapovan Vishnugad dam, Helang-Marwari bypass road) may have exacerbated the situation (Upadhyay, Kavita, Jan 2023). This irreversible loss is a harbinger of worse to come.
Sadly, land subsidence incidents in hilly urban India are increasingly common. ~12.6% of India’s land area is prone to landslides, with some of this falling in hilly urban regions of Sikkim, West Bengal, Uttarakhand etc. Urban policy makes this worse – as per the National Institute for Disaster Management (and in the National Landslide Risk Management Strategy, Sep 2019), construction in such landscapes is often driven by building byelaws that ignore local geological and environmental factors (Moudgil, Manu, Oct 2020). Consequently, land use planning in Himalayan towns and the Western Ghats is often ill-conceived when planned, and primarily unplanned – all adding up to slope instability. As a result, landslide vulnerability has risen, exacerbated by tunnelling construction that weakens rock formations.
A first step towards enhancing urban resilience with regard to land subsidence requires credible data. We need to map landslide risk at a granular level. The Geological Survey of India has conducted a national mapping exercise (at a 1:50,000 scale, with each cm denoting ~0.5km). Urban policymakers need to take this further, with additional detail and localization (e.g. at a 1:1000 scale) (Moudgil, Manu, Oct 2020). Areas with high landslide risk should not be allowed to expand large infrastructure, with a push to reduce human interventions and adhere to carrying capacity. Select examples show the way – Aizawl, in Mizoram, is in Seismic Zone V, and is built on very steep slopes – an earthquake with a magnitude greater than 7 would easily trigger over 1,000 landslides, collapsing 13,000 buildings (Moudgil, Manu, Oct 2020). The city has prepared by developing a landslide action plan (with a push to reach 1:500 scale), and updated regulations to guide construction activities in hazardous zones. The city’s landslide policy committee is cross-disciplinary in nature, and seeks inputs from civic society and university students, with a push to continually update risk zones.
Furthermore, any site development in hazardous zones requires assessment by a geologist (w.r.t soil suitability and slope stability) and an evaluation of the potential impact on nearby buildings. Corrective measures (e.g. retention walls) are then required, with a push to prohibit construction in hazardous areas. In Gangtok, Amrita Vishwa Vidyapeetham has helped set up a real-time landslide monitoring and early warning system, with multiple sensors highlighting the impact of rainfall infiltration, water movement and slope instability (Moudgil, Manu, Oct 2020).
Beyond land subsidence, flood risk is also becoming frequent. In August 2019, the township of Palava City (Phase I and II) in Dombivli in Maharashtra was flooded, with ~5 ft water depth in much of Phase I – incessant rain led to vehicles being submerged and electricity connections being switched off (Gupta, Pradeep, Aug 2019). Residents were stranded in their flats until the water was drained out using pumps. While seasonal downpours have increased in intensity, the impact of seasonal flooding was worsened by a simple fact – the township, spread over 4,500 acres, was built on the flood plains of the river Mothali! When planned townships are approved, with a distinct lack of concern for natural hazards, such incidents are bound to occur. Such tales are awfully familiar – Panjim was hit by floods in July 2021 – incessant rains led to local rivers swelling up and flooding homes, with urban settlements along the Mandovi affected in particular (Lobo, Aaron Savio, Bhandari, Ashali, Kuppu, Karthikeyan, Mar 2022). Again, urban planning had a role to play – the city, built on the marshlands that lie astride on the floodplains of the river Mandovi, was once fringed by mangroves and fertile fields, which helped bolster its flood resilience.
Meanwhile, other cities continue to face a high risk of flooding in the near future – in Delhi, there are ~9,350 households living in Yamuna floodplains (Hargovind, Abhinaya, Mar 2022). IPCC’s report (in March 2022) highlighted that Kolkata faced a significant risk of subsidence due to a rise in sea levels and flooding. Poor urban planning, combined with climate change, will mean that our cities will be perennially flooded.
Flood-proofing our cities will require measures on various axes – urban planners will have to temper the push to fill up local water bodies, canals and drains and focus on enhancing sewerage and the stormwater drain network. Existing sewerage networks need to be expanded, in coverage and depth, to enable wastewater in low-lying urban geographies to drain away. Additionally, there needs to be a push to desilt rivers that frequently overflow, along with a push for coastal walls in areas at risk from sea rise. Beyond this, greater spending on building flood-resilient architecture (e.g. constructing river embankments, constructing flood shelters in coastal areas), along with flood warning systems, is necessary (Parida, Yashobanta, Bharadwaj, Parul, Sahoo, Prakash Kumar, Aug 2022). In addition, there needs to be a push for protecting “blue infra” areas – i.e. places that act as natural sponges for absorbing surface runoff, allowing groundwater to be recharged. As rainfall patterns and intensity change, urban authorities will need to invest in simulation capacity to determine flooding hotspots and flood risk maps, along with integrating relief efforts (Prakash, Anjal, Goswami, Aishani, Aug 2020).
Urban India doesn’t have to embrace such risks. We can mitigate them – if our cities proactively incorporate environmental planning, with a push for enhancing natural open spaces. Urban master plans need to consider the impact of climate change and extreme weather (e.g. planning for ~125 mm per hour peak rainfall in Bengaluru in the future, vs 75 mm currently; Shakeel, Shobhan, Nov 2022). Urban authorities in India should continually assess and update disaster risk and preparedness planning. Early warning systems will also be critical (Rajshekhar, M., Jan 2021). Finally, each city needs to have a disaster management framework in place, with a push for having large arterial roads that allow people and goods to move in and out of the city at pace. Our urban journey is not limited to an election cycle – we must plan for a multi-generational process.
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