FOREWORD he High Plains aquifer is the principal source for irrigation and drinking water in one of the major agricultural areas in the Nation. For any natural resource (for example, water, minerals, or energy), decisions about future utilizations depend on having a clear understanding of the status of the resource, the amount that has already been extracted, the amount remaining, and the impact of further depletion. This Circular reports on the available water in the High Plains aquifer in 2000 and the changes that have taken place in recent decades. The Circular is intended to help those who are interested or involved in the protection, management, and sustainable use of the High Plains aquifer to understand it better and make the best possible decisions. The information is based on the cooperative efforts of local, State, and Federal agencies to monitor water levels throughout the aquifer on a regular basis. V

SI to Inch/Pound Multiply By To obtain Length meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) Area square meter (m 2) 0.0002471 acre hectare (ha) 2.471 acre Volume cubic meter (m 3) 0.00081 acre-foot Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:°F =(1.8×°C)+32 Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:°C =(°F-32)/1.8 Datum information used in this report Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD29). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Elevation, as used in this report, refers to distance above the vertical datum.

The U.S. Geological Survey (USGS) is committed to providing the Nation with accurate and timely scientific information that helps enhance and protect the overall quality of life and that facilitates effective management of water, biological, energy, and mineral resources (http://www.usgs.gov/). Information on the quality of the Nation's water resources is critical to assuring the long-term availability of water that is safe for drinking and recreation and suitable for industry, irrigation, and habitat for fish and wildlife. Population growth and increasing demands for multiple water uses make water availability, now measured in terms of quantity and quality, even more essential to the long-term sustainability of our communities and ecosystems. The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support national, regional, and local information needs and decisions related to water-quality management and policy (http://water.usgs.gov/nawqa). Shaped by and coordinated with ongoing efforts of other Federal, State, and local agencies, the NAWQA Program is designed to answer: What is the condition of our Nation's streams and ground water? How are the conditions changing over time? How do natural features and human activities affect the quality of streams and ground water, and where are those effects most pronounced? By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, the NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities. From 1991-2001, the NAWQA Program completed interdisciplinary assessments in 51 of the Nation's major river basins and aquifer systems, referred to as Study Units (http://water.usgs.gov/nawqa/ studyu.html). Baseline conditions were established for comparison to future assessments, and long-term monitoring was initiated in many of the basins. During the next decade, 42 of the 51 Study Units will be reassessed so that 10 years of comparable monitoring data will be available to determine trends at many of the Nation's streams and aquifers. The next 10 years of study also will fill in critical gaps in characterizing water-quality conditions, enhance understanding of factors that affect water quality, and establish links between sources of contaminants, the transport of those contaminants through the hydrologic system, and the potential effects of contaminants on humans and aquatic ecosystems. The USGS aims to disseminate credible, timely, and relevant science information to inform practical and effective water-resource management and strategies that protect and restore water quality. We hope this NAWQA publication will provide you with insights and information to meet your needs, and will foster increased citizen awareness and involvement in the protection and restoration of our Nation's waters. The USGS recognizes that a national assessment by a single program cannot address all waterresource issues of interest. External coordination at all levels is critical for a...

Since the early 1900s, groundwater has been the primary source of municipal, industrial, and agricultural water supplies for the Houston-Galveston region, Texas. The region's combination of hydrogeology and nearly century-long use of groundwater has resulted in one of the largest areas of subsidence in the United States; by 1979, as much as 3 meters (m) of subsidence had occurred, and approximately 8,300 square kilometers of land had subsided more than 0.3 m. The U.S. Geological Survey, in cooperation with the Harris-Galveston Subsidence District, used interferometric synthetic aperture radar (InSAR) data obtained for four overlapping scenes from European remote sensing satellites ERS-1 and ERS-2 to analyze land subsidence in the Houston-Galveston region of Texas. The InSAR data were processed into 27 interferograms that delineate and quantify land-subsidence patterns and magnitudes. Contemporaneous data from the Global Positioning System (GPS) were reprocessed by the National Geodetic Survey and analyzed to support, verify, and provide temporal resolution to the InSAR investigation. The interferograms show that the area of historical subsidence in downtown Houston along the Houston Ship Channel has stabilized and that recent subsidence occurs farther west and north of Galveston Bay. Three areas of recent subsidence were delineated along a broad arcuate (bowshaped) feature from Spring, Tex., southwest to Cypress, Tex., and south to Sugar Land, Tex., with subsidence rates ranging from 15 millimeters per year (mm/yr) to greater than 60 mm/ yr. Multiyear interferograms near Seabrook, Tex., within the historical subsidence area and nearby Galveston Bay, show several fringes of subsidence (approximately 85 millimeters from January 1996 to December 1997) in the area; however it is difficult to determine the subsidence magnitude near Seabrook because many of the InSAR fringes were truncated or ill-defined. Horizontal and vertical GPS data throughout the area support the InSAR measured subsidence rates and extent. The subsidence rates for a few GPS stations northwest of Houston began to decrease in 2007, which may indicate that subsidence may be decreasing in these areas.

] 1. Map showing approximate 2016 water-level altitudes in the Chicot aquifer, Houston-Galveston region, Texas. 2. Map showing water-level changes in the Chicot aquifer, Houston-Galveston region, Texas, 2015-16. 3. Map showing approximate water-level changes in the Chicot aquifer, Houston-Galveston region, Texas, 2011-16. 4. Map showing approximate water-level changes in the Chicot aquifer, Houston-Galveston region, Texas, 1990-2016. 5. Map showing approximate water-level changes in the Chicot aquifer, Houston-Galveston region, Texas, 1977-2016. 6. Map showing approximate 2016 water-level altitudes in the Evangeline aquifer, Houston-Galveston region, Texas. 7. Map showing water-level changes in the Evangeline aquifer, Houston-Galveston region, Texas, 2015-16. 8. Map showing approximate water-level changes in the Evangeline aquifer, Houston-Galveston region, Texas, 2011-16. 9. Map showing approximate water-level changes in the Evangeline aquifer, Houston-Galveston region, Texas, 1990-2016. 10. Map showing approximate water-level changes in the Evangeline aquifer, Houston-Galveston region, Texas, 1977-2016. 11. Map showing approximate 2016 water-level altitudes in the Jasper aquifer, Houston-Galveston region, Texas. 12. Map showing water-level changes in the Jasper aquifer, Houston-Galveston region, Texas, 2015-16. 13. Map showing approximate water-level changes in the Jasper aquifer, Houston-Galveston region, Texas, 2011-16. 14. Map showing approximate water-level changes in the Jasper aquifer, Houston-Galveston region, Texas, 2000-16. 15. Map showing locations of borehole-extensometer sites, Houston-Galveston region, Texas, 2015. 16. Graphs showing measured cumulative compaction of subsurface sediments at borehole-extensometer sites depicted on sheet 15, 1973-2015. 1. Map showing locations of groundwater regulatory districts; approximate traces of hydrogeologic sections A-A´, B-B´, and C-C´;