Geomorphologic Domination on Urban Sprawl of Southern Riyadh, Saudi Arabia Using Differential Interferometric Synthetic Aperture Radar (DInSAR)

This study tests the southern part of the Riyadh City growth domination by the Early Quaternary-Holocene trans-tensional Central Arabian graben system reactivation and the subsequent dissolution-induced collapses and karstification. This study utilizes Synthetic Aperture Radar (SAR) and Differential Interferometric Synthetic Aperture Radar (DinSAR) to examine the morphology of arid landscape, south of Riyadh. Eight Single Look Complex (SLC) amplitude images are calibrated, filtered, georeferenced and orthorectified at a resolution of 20 meters, and compared with one another by producing 17 diachronic images of the pairs at different intervals (1996, 2003-2005, 2008). The diachronic SAR intensity imageries suggest a downthrown displacement reaching 600 m and eastward tilting at the bottoms of the grabens. Also, the structurally-controlled valleys are developing an eastward-running drainage system towards the oasis of Al-Kharj and capturing an older hydrologic system. Moreover, a 12-year period (1996-2008) of the SAR data was obtained to examine the average annual rate of southern Riyadh’s urban sprawl, which is estimated at approximately 390 metres/year over the 12 years and constrained by geomorphological features towards the deformed area. DInSAR imageries show the primary results obtained from the 26 May 2004 and 31 Jan. 2005 pair of images, merged with 30 m resolution DEM-SRTM data for the arid region south of Riyadh to eliminate the influence of topography. DInSAR is applied in this study for its ability to detect small displacements at the centimetre scale (1/2 wavelength). Although the DInSAR’s coherence and phase imageries suggest a fairly stable region since the last tectonic and subsequent geomorphic events, erosional and artificial changes are observed, bounded within the valleys and depressions, primarily due to aeolian and fluvial processes and agriculture. It is highly recommended to preserve the area for sustainability and economy.