Date of Award

12-2017

Degree Name

Doctor of Philosophy

Department

Geosciences

First Advisor

Dr. Mohamed Sultan

Second Advisor

Dr. Alan Kehew

Third Advisor

Dr. William Sauck

Fourth Advisor

Dr. Richard Becker

Keywords

Land deformation, subsidence, mega aquifer system, groundwater, InSAR, Saudi Arabia

Abstract

Deformational features such as subsidence, sinkholes, fissures, settling and cracks in buildings and structures, and earthquakes are being reported from many of the world’s arid lands, in areas where fossil aquifers are being excessively exploited. Using the Lower Mega Aquifer System (LMAS) in Arabia as a test site, I applied an integrated approach (remote sensing, geodesy, GIS, geology, hydrogeology, and geotechnical) to identify nature, intensity, spatial distribution, and factors controlling the observed deformation in the central (Al-Qassim and Ha'il regions; area: 16×10⁴ km²) and the northern (Wadi As-Sirhan Basin; area: ~10.9×10⁴ km²) Arabia. A four -fold approach was adopted to accomplish the following: (1) assess the spatial distribution of land deformation and quantify deformation rates using field and Interferometric Synthetic Aperture Radar (InSAR) and Persistent Scatterer Interferometry (PSI) methods (period: 2003 to 2012); (2) estimate aquifer depletion rates using temporal (04/2002-06/2016) Gravity Recovery and Climate Experiment (GRACE) solutions; (3) generate a GIS database to host all relevant data and derived products (e.g., remote sensing, geology, geotechnical, GPS, groundwater extraction rates, and water levels, etc.) and to conduct spatial correlations of these spatial and temporal datasets in search of causal effects; and (4) identify extraction scenarios to attain sustainable utilization and to minimize land deformation. The following observations are consistent with deformational features being caused by excessive groundwater extraction: (1) distribution of deformational features correlated spatially and temporally with increased agricultural development and groundwater extraction, decline in water levels and in groundwater storage; (2) earthquake events (1.5 - 5.5 M) increased from a single event at the onset of the agricultural development program in 1980 (extraction: 1 km³/yr), up to 13 events per year in the nineties, the decade that witnessed the largest expansion in groundwater extraction (average annual extraction: >6.4 km³) and land reclamation; and (3) earthquake epicenters and the deformation sites are found largely within areas bound by the Kahf fault system suggesting that faults play a role in localizing deformation. Findings from the PSI investigation revealed high, yet irregularly distributed, subsidence rates (-4 to -15 mm/yr) along a NW-SE trending graben within the Wadi As-Sirhan with the highest subsidence rates being localized within elongated bowls, that are proximal to, or bound by, the major faults and that areas to the east and west of the bounding faults show no, or minimal subsidence. Findings from the analysis of GRACE data indicate that sustainable extraction from the LMAS could be attained by reducing groundwater extraction by 3.5 to 4 km³/yr and provide replicable and cost-effective methodologies for optimum utilization of fossil aquifers and for minimizing the deformational effects associated with their utilization.

Access Setting

Dissertation-Open Access

Download

Share

COinS