Detecting Sinkhole and Land Deformation Hazards Related to Carbonate Dissolution in Qatar using Geodetic Methods

The majority of sinkholes and other large karst features in the State of Qatar in particular, and in the Arabian Peninsula in general, were formed during paleo wet climatic periods in the Pleistocene by dissolution of carbonates and evaporates that cover large sectors of the country. We employed integrated research approach (remote sensing, field, geodesy) to investigate the general pattern of land deformation in Qatar, identify and detect suspected sinkhole locations, and investigate the processes and factors that are causing land subsidence and formation of sinkholes. We applied the small baseline subset (SBAS) technique interferometric method on 9 Envisat ASAR scenes to investigate the deformation pattern over a span of 8 years (2003 - 2009) and calibrated our results against 6 GPS stations. The extracted deformation rates were correlated in a GIS environment with relevant datasets in search of causal effects. These include surface and subsurface geology, orientation and distribution of geological structures, depressions inferred from high-resolution digital elevation model (DEM), distribution and intensity of rainfall, temporal and spatial variations in groundwater levels, distribution of Treated Sewage Effluent (TSE) wells, and land use and land cover. Our findings include: (1) high subsidence rates (-5 to -7 mm/yr) were detected along reclaimed coastal areas south and east Doha (south east of Umm Salal town), areas that are underlain by the Upper Dammam formation chalky limestone; (2) moderate to high deformation rates (-4 to -6 mm/yr) were observed over the gypsiferous sabkha of Ras Laffan, Al Khor, and along the western coastal areas of Qatar and over the Dukhan depression/oil field; (3) moderate subsidence rates (-2 to -4 mm/yr) over groundwater-fed (from Rus and Umm er Radhuma aquifers) agricultural fields in north and central Qatar; (4) spatial correspondence between the distribution of TSE injection wells and moderate subsidence rates (-2 to -5 mm/yr) possibly indicating the dissolutive impact of the injected TSE (water) on the soluble layers in the subsurface; and (5) depressions inferred from DEM (area: 1 - 5 km²), mostly in the south and eastern areas, lie within or near ( 100 m) moderate to high subsiding (-2 to -6 mm/yr) areas and could potentially grow into sinkholes.