Subsidence Due To Groundwater Exploitation Using InSAR Technique Over Chandigarh-Mohali Regions Of Northern India
Authors: Chawla Shivam , Ojha Chandrakanta , Shirzaei Manoochehr 
Published: February 2023

The Indo-Gangetic plain (IGP) in Northern India is one of the crucial aquifer systems, which depicts a declining trend of groundwater levels due to anthropogenic activities over a period from 2000 to 2012 (Mcdonald et al., 2016). The Gravity Recovery and Climate Experiment (GRACE) satellite have already illustrated a substantial decline in total water storage from 2000 to 2008 over in the northwestern part of India (Rodell et al., 2009). However, this study focused on Mohali and Chandigarh study areas, one of the emerging metropolitan planned cities of East Punjab and the union territory of India, for understanding groundwater dynamics using an advanced satellite radar interferometry technique (InSAR). Here, we explored Synthetic Aperture Radar (SAR) datasets with ascending and descending orbital tracks of Sentinel-1A/B sensors of the European Space Agency (ESA) to compute vertical land motion (VLM) during the study period from November 2015 to August 2022. 175 acquisitions of ascending and 170 imageries of descending orbital paths were used for generating the InSAR data processing. For ascending datasets, 638 suitable interferograms were generated with suitable temporal-spatial baseline thresholds of 75 days and 80 meters, respectively. Similarly, 574 interferograms were considered for descending datasets with temporal-spatial baseline thresholds of 80 days and 100 meters, respectively. The data processing has been carried out using Multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR) technique using the Small BAseline Subset (SBAS) algorithm on GMTSAR software for generating a Line of Sight (LOS) velocity map (Sandwell et al., 2011). Further, the InSAR-derived results from both tracks were combined to compute the VLM of the study area (Fuhrmann et al., 2019). The observation shows a significant deformation signal in the Mohali and Chandigarh regions. In particular, about 18 cm/yr of VLM rate was noticed in Mohali, 16cm/yr in Kharar, 17cm/yr in Dera Bassi, 12 cm/yr in Lalru of SAS Nagar districts, and 8cm/yr in the south-eastern part of Chandigarh during the study period. However, the water level shows a total 6.45 meters below ground level (mbgl) with a declining trend of 0.645 mbgl/yr in Mohali compared to surrounding regions, whereas Chandigarh city exhibits 0.593 mbgl/yr GW rate with a total head level change of 5.93 mbgl during the observation period of 2011 to 2021, which demonstrates a good correlation with the InSAR VLM. Our ongoing investigation is carried out to understand further the groundwater dynamics of the aquifer system and local scale subsidence over different parts of the cities.REFERENCES&#160; &#160; &#160; &#160;&#160;&#160;MacDonald, A. M., et al. "Groundwater quality and depletion in the Indo-Gangetic Basin mapped from in situ observations."&#160;Nature Geoscience&#160;9.10 (2016): 762-766.
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