SUBSIDENCE MONITORING USING THE DINSAR TECHNIQUE ALONG THE COASTAL REGION OF NIGERIA: A CASE STUDY OF LAGOS CITY, LAGOS STATE

The worldwide geohazard of land subsidence emerges from natural environmental changes and human activities which mostly stem from excessive groundwater extraction. The situation creates dangerous threats which endanger the safety of built structures while making coastal cities in urban areas more prone to flooding events. The groundwater extraction practices in Lagos Nigeria create the highest risk because people operate numerous private water wells and the city builds rapidly on unstable coastal soil. The study uses Differential Interferometric Synthetic Aperture Radar (DInSAR) technique to measure and study ground movement in Lagos from January 2016 through December 2019. A total of 35 descending-pass Sentinel-1 SAR images were processed using the SeNtinel-1 Application Platform (SNAP). The results reveal that 51.33% of Lagos is affected by low subsidence velocities (−2.5 to −5 mm/year), while 21.56% experiences high subsidence rates exceeding −5 mm/year. The city shows stability in 25.36% of its area because the ground displacement stays between −2.5 and 2.5 mm/year while only 0.14% of the land experiences slight elevation changes. The alluvial deposits together with coastal environments form the areas which experience high subsidence because sediment compaction and aquifer system response to intensive groundwater withdrawal. The areas which experience the most subsidence include Ikeja and Lekki and Badagry and Victoria Island because their geological features combine with groundwater extraction and substantial building weights. The research establishes that DInSAR technology offers a dependable monitoring system which delivers precise results across large areas for deformation analysis better than traditional methods that rely on ground measurements. The research findings offer vital scientific proof which supports the development of sustainable urban planning systems and geohazard reduction methods and flood-risk control systems for Lagos.