AN INTEGRATED APPROACH (INSAR TIME SERIES, HYDROLOGY, SPATIAL ANALYSIS) TO IDENTIFY THE NATURE, INTENSITY, AND SPATIAL DISTRIBUTION OF GROUND DEFORMATION OVER RIYADH CITY AND SURROUNDINGS

Over the past three to four decades ground deformation-related features (e.g., sink holes, fissures, subsidence) that resulted in loss of property and lives were reported from the City of Riyadh and from its surroundings in Saudi Arabia. The recent advances in InSAR time series analysis techniques and availability of SAR imagery worldwide, is now enabling reliable measurement of ground deformation. We investigated the nature, intensity and spatial distribution of ground deformation in Riyadh city using InSAR time series technologies and compared our findings to relevant datasets. A series of 27 Sentinel-1 images acquired between August 2016 and March 2018 was selected and the InSAR Small Baseline Subset (SBAS) method was adopted. The factors controlling the observed deformation were investigated by conducting spatial and temporal correlations between the observed surface deformation rates with relevant datasets (e.g., temporal and spatial variations in groundwater levels, surface and subsurface lithologies, distribution of caves and sinkholes, landuse and landcover, and optical multitemporal imagery). Findings Include (1) over 90 sites were identified with high subsidence rates up to -15 mm/yr including buildings, railroads, highways, dumps sites of mining activities, fill areas for construction and suspected sinkhole/cavity formations, (2) majority of the buildings/roads experiencing high rates of subsidence were constructed recently (after 2014) indicating consolidation of fill material used prior to the construction and/or settling of the subsurface material due to the load of the building, and (3) observed subsidence rate for a few of the buildings seems to be slowing down in the more recent months perhaps due to a reduction in the compaction rates of sediments underlying these buildings with time.