Decadal Earth observation-informed analysis of urban riverbank deformation: InSAR insights into soft ground dynamics in Nanjing, China

Abstract

The rapid urbanization of urban riverbank soft ground poses significant geotechnical challenges, particularly in densely populated coastal areas like the Yangtze River Delta. This study employs an enhanced multi-temporal Interferometric Synthetic Aperture Radar (InSAR) approach to reveal decadal deformation patterns (2015–2024) in soft ground along the Yangtze River in Nanjing, China. Leveraging 275 Sentinel-1 SAR images and improved data processing strategies, we reconstruct the subsidence dynamics and validate them against leveling measurements with an accuracy of 6.5 mm/a. Results reveal that while the overall Nanjing’s urban riverbank remains stable, localized deformations are concentrated in urban riverbank development zones: Jiangbei New Area (JBA) and Hexi New Town (HXT). The highest intensity of development in JBA shows a cumulative settlement of more than 600 mm over ten years. The soft ground deformation is driven by engineering activities, specifically (i) groundwater drawdown during foundation pit dewatering and (ii) consolidation under surcharge loads from riverbank urban infrastructure. The earlier-developed HXT provides a valuable reference for predicting surface deformation trends in JBA. Furthermore, decadal InSAR deformation analyses of critical urban riverbank infrastructure (river-crossing bridges) confirm the effectiveness of bedrock anchoring in mitigating soft ground settlement. Wavelet analyses reveal that temperature fluctuations primarily drive cyclic displacement in the metal truss main spans of the Beijing-Shanghai High-Speed Railway Nanjing Yangtze River Bridge. This work demonstrates the decisive influence of anthropogenic activities in accelerating subsidence and reveals the efficacy of InSAR in supporting adaptive risk mitigation strategies. The findings provide actionable insights for sustainable urban riverbank development in soft ground regions, emphasizing the need for integrated monitoring and ground improvement measures to enhance infrastructure resilience in global deltaic cities undergoing riverbank urbanization.