Investigation of Land Subsidence in the Houston-Galveston Region of Texas By Using the Global Positioning System and Interferometric Synthetic Aperture Radar, 1993?2000

The Houston-Galveston region-comprising Harris and Galveston Counties and adjacent parts of Brazoria, Chambers, Fort Bend, Grimes, Liberty, Montgomery, San Jacinto, Walker, and Waller Counties (fig. 1)-is one of the largest areas of subsidence in the United States (Galloway and others, 1999). Most of the subsidence in the Houston-Galveston region (which includes the greater Houston metropolitan area) has occurred as a direct result of groundwater withdrawals for municipal supply, industrial use, and irrigation that depressured and dewatered the major aquifers in the area, thereby causing compaction of the clay layers of the aquifer sediments (Kasmarek and others, 2010; Johnson and others, 2011). Groundwater has historically been the principal source of water for municipal, industrial, and agricultural uses, and groundwater use in the Houston-Galveston region had increased rapidly for many decades to meet the water needs of the rapidly growing population (Seifert and Drabek, 2006). Since the 1990s, surface water has been increasingly used to meet these water needs and reduce reliance on groundwater resources in the Houston-Galveston region (Kasmarek and Robinson, 2004).