Geology topics

Mark C. Kasmarek

Publications and source records attributed to Mark C. Kasmarek.

At least 19 recordsLinked to original sources

USGS2017

Water-level altitudes 2017 and water-level changes in the Chicot, Evangeline, and Jasper Aquifers and compaction 1973–2016 in the Chicot and Evangeline Aquifers, Houston-Galveston region, Texas

Most of the land-surface subsidence in the Houston-Galveston region, Texas, has occurred as a direct result of groundwater withdrawals for municipal supply, commercial and industrial use, and irrigation that depressured and dewatered the Chicot and Evangeline aquifers, thereby causing compaction of the aquifer sediments, mostly in the fine-grained silt and clay layers. This report, prepared by the U.S. Geological Survey in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, Lone Star Groundwater Conservation District, and Brazoria County Groundwater Conservation District, is one in an annual series of reports depicting water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers and measured cumulative compaction of subsurface sediments in the Chicot and Evangeline aquifers in the Houston-Galveston region. This report contains regional-scale maps depicting approximate 2017 water-level altitudes (represented by measurements made during December 2016 through March 2017) and long-term water-level changes for the Chicot, Evangeline, and Jasper aquifers; a map depicting locations of borehole-extensometer (hereinafter referred to as “extensometer”) sites; and graphs depicting measured long-term cumulative compaction of subsurface sediments at the extensometers during 1973–2016. In 2017, water-level-altitude contours for the Chicot aquifer ranged from 200 feet (ft) below the North American Vertical Datum of 1988 (hereinafter referred to as “datum”) in two localized areas in southwestern and northwestern Harris County to 200 ft above datum in west-central Montgomery County. The largest water-level-altitude decline (120 ft) depicted by the 1977–2017 water-level-change contours for the Chicot aquifer was in northwestern Harris County. A broad area where water-level altitudes declined in the Chicot aquifer extends from northwestern, north-central, and southwestern Harris County across parts of north-central, eastern, and south-central Fort Bend County into southeastern Waller County. Adjacent to the areas where water levels declined was a broad area where water levels rose in central, eastern, and southeastern Harris County, most of Galveston County, eastern and northernmost Brazoria County, and northeastern Fort Bend County. The largest rise (200 ft) in water-level altitudes in the Chicot aquifer from 1977 to 2017 was in southeastern Harris County. The water-level-altitude contours for the Evangeline aquifer in 2017 indicated two areas where the water-level altitudes were 250 ft below datum—one area extending from south-central Montgomery County into north-central Harris County and another area in western Harris County. Water-level altitudes in the Evangeline aquifer ranged from 50 to 200 ft below datum throughout most of Harris County in 2017. In Montgomery County, water-level altitudes in the Evangeline aquifer in 2017 ranged from the aforementioned area where they were 250 ft below datum to an area where they were 200 ft above datum in the northwestern part of the county. The 1977–2017 water-level-change contours for the Evangeline aquifer depict a broad area where water-level altitudes declined in north-central Harris and south-central Montgomery Counties, extending through north-central, northwestern, and southwestern Harris County into western Liberty, southeastern and northeastern Waller, and northeastern and east-central Fort Bend Counties. The largest water-level-altitude decline (280 ft) was in north-central Harris and south-central Montgomery Counties. Water-level altitudes rose in a broad area from central, east-central, and southern Harris County extending into the northernmost part of Brazoria County, the northernmost part of Galveston County, and the southwestern area of Liberty County. The largest rise in water-level altitudes in the Evangeline aquifer from 1977 to 2017 (240 ft) was in southeastern Harris County. Water-level-altitude contours for the Jasper aquifer in 2017 ranged from 200 ft below datum in three isolated areas of south-central Montgomery County (the westernmost of these areas extended slightly into north-central Harris County) to 250 ft above datum in extreme northwestern Montgomery County, northeastern Grimes County, and southwestern Walker County. The 2000–17 water-level-change contours for the Jasper aquifer depict water-level declines in a broad area throughout most of Montgomery County and in parts of Waller, Grimes, and Harris Counties, with the largest decline (220 ft) in an isolated area in south-central Montgomery County. Compaction of subsurface sediments (mostly in the fine-grained silt and clay layers) in the Chicot and Evangeline aquifers was recorded continuously by using 13 extensometers at 11 sites that were either activated or installed between 1973 and 1980. During the period of record beginning in 1973 (or later depending on activation or installation date) and ending in late November or December 2016, measured cumulative compaction at the 13 extensometers ranged from 0.096 ft at the Texas City-Moses Lake extensometer to 3.700 ft at the Addicks extensometer. From January through late November or December 2016, the Addicks, Lake Houston, Southwest, and Northeast extensometers recorded net decreases in land-surface elevation, but the Baytown C–1 (shallow), Baytown C–2 (deep), Clear Lake (shallow), Clear Lake (deep), East End, Johnson Space Center, Pasadena, Seabrook, and Texas City-Moses Lake extensometers recorded net increases in land-surface elevation. The rate of compaction varies from site to site because of differences in rates of groundwater withdrawal in the areas adjacent to each extensometer site; differences among sites in the ratios of sand, silt, and clay and their corresponding compressibilities; and previously established preconsolidation heads. It is not appropriate, therefore, to extrapolate or infer a rate of compaction for an adjacent area on the basis of the rate of compaction recorded by proximal extensometers.

Texas↗

USGS2016

Water-level altitudes 2016 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973–2015 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

Most of the land-surface subsidence in the Houston-Galveston region, Texas, has occurred as a direct result of groundwater withdrawals for municipal supply, commercial and industrial use, and irrigation that depressured and dewatered the Chicot and Evangeline aquifers, thereby causing compaction of the aquifer sediments, mostly in the fine-grained silt and clay layers. This report, prepared by the U.S. Geological Survey in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, Lone Star Groundwater Conservation District, and Brazoria County Groundwater Conservation District, is one in an annual series of reports depicting water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers and measured cumulative compaction of subsurface sediments in the Chicot and Evangeline aquifers in the Houston-Galveston region. The report contains regional-scale maps depicting approximate 2016 water-level altitudes (represented by measurements made during December 2015–March 2016) for the Chicot, Evangeline, and Jasper aquifers; maps depicting 1-year (2015–16) water-level changes for each aquifer; maps depicting approximate contoured 5-year (2011–16) water-level changes for each aquifer; maps depicting approximate contoured long-term (1990–2016 and 1977–2016) water-level changes for the Chicot and Evangeline aquifers; a map depicting approximate contoured long-term (2000–16) water-level changes for the Jasper aquifer; a map depicting locations of borehole-extensometer sites; and graphs depicting measured long-term cumulative compaction of subsurface sediments at the extensometers during 1973–2015. Tables listing the water-level data used to construct each water-level map for each aquifer and the measured long-term cumulative compaction data for each extensometer site are included. Graphs depicting water-level measurement data also are included; these graphs can be used to approximate changes in effective stress caused by changes in groundwater withdrawal from the Chicot and Evangeline aquifers. In 2016, water-level-altitude contours for the Chicot aquifer ranged from 200 feet (ft) below the vertical datum (North American Vertical Datum of 1988; hereinafter, datum) in a localized area in northwestern Harris County to 200 ft above datum in west-central Montgomery County. Water-level changes during 2015–16 in the Chicot aquifer ranged from a 39-ft decline to a 26-ft rise. Contoured 5-year and long-term changes in water-level altitudes of the Chicot aquifer ranged from a 30-ft decline to a 20-ft rise (2011–16), from a 140-ft decline to a 160-ft rise (1990–2016), and from a 120-ft decline to a 200-ft rise (1977–2016). In 2016, water-level-altitude contours for the Evangeline aquifer ranged from 250 ft below datum in three separate areas in south-central Montgomery County and extending into north-central Harris County, in west-central Harris County, and in southwestern Harris County to 200 ft above datum in southeastern Grimes and northwestern Montgomery Counties. Water-level changes during 2015–16 in the Evangeline aquifer ranged from a 65-ft decline to a 61-ft rise. Contoured 5-year and long-term changes in water-level altitudes of the Evangeline aquifer ranged from a 60-ft decline to a 40-ft rise (2011–16), from a 160-ft decline to a 160-ft rise (1990–2016), and from a 320-ft decline to a 240-ft rise (1977–2016). In 2016, water-level-altitude contours for the Jasper aquifer ranged from 200 ft below datum in south-central Montgomery County extending into north-central Harris County to 250 ft above datum in northwestern Montgomery County and extending into eastern Grimes County and southwestern Walker County. Water-level changes during 2015–16 in the Jasper aquifer ranged from a 38-ft decline to a 51-ft rise. Contoured 5-year and long-term changes in water-level altitudes of the Jasper aquifer ranged from a 60-ft decline to a 40-ft rise (2011–16) and from a 220-ft decline to a 20-ft decline (2000–16). Compaction of subsurface sediments (mostly in the fine-grained silt and clay layers) in the Chicot and Evangeline aquifers was recorded continuously by using 13 extensometers at 11 sites that were either activated or installed between 1973 and 1980. During the period of record beginning in 1973 (or later depending on activation or installation date) and ending in December 2015, measured cumulative compaction at the 13 extensometers ranged from 0.095 ft at the Texas City-Moses Lake extensometer to 3.666 ft at the Addicks extensometer. From January through December 2015, the Northeast, Southwest, Addicks, Johnson Space Center, and Clear Lake (deep) extensometers recorded net decreases in land-surface elevation, but the Lake Houston, East End, Texas City-Moses Lake, Baytown C–1 (shallow), Baytown C–2 (deep), Seabrook, Clear Lake (shallow), and Pasadena extensometers recorded net increases in land-surface elevation. For the 11 extensometer sites during the selected years 1988, 1998, 2008, 2012, and 2015, the smallest effective stress (20.12 pounds per square inch [psi]) was estimated at the Texas City-Moses Lake extensometer site and was produced by a measured water level of 46.42 ft below land-surface datum (blsd) in January 2008. The corresponding net compaction during 2007 at this site was 0.001 ft. The largest effective stress (174.86 psi) was estimated at the Addicks extensometer site and was produced by a measured water level of 403.38 ft blsd in January 1998. The corresponding net compaction at the Addicks site was 0.067 ft in 1997. The 2011 drought caused water-level declines in the aquifers that were documented by the water-level-measurement data collected in January 2012. During the 2011 drought, the 13 extensometers recorded varying amounts of compaction that ranged from a net compaction value of 0.002 ft recorded by the Texas City-Moses Lake extensometer to a net compaction value of 0.192 ft recorded by the Pasadena extensometer. Water-level data for 1988, 1998, 2008, 2012, and 2015 and the corresponding net compaction values recorded by the extensometers for 1987, 1997, 2007, 2011, and 2014 were used to illustrate the cause and effect relations between changes in water level caused by groundwater withdrawals and resulting changes in effective stress. Changes in effective stress are related to changes in land-surface elevations caused by compaction of the fine-grained sediments composing the Chicot and Evangeline aquifers. The rate of compaction varies from site to site because of differences in rates of groundwater withdrawal in the areas adjacent to each extensometer site; differences among sites in the ratios of sand, silt, and clay and their corresponding compressibilities; and previously established preconsolidation heads. It is not appropriate, therefore, to extrapolate or infer a rate of compaction for an adjacent area on the basis of the rate of compaction recorded by proximal extensometers.

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USGS2015

Water-level altitudes 2015 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2014 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

Most of the land-surface subsidence in the Houston-Galveston region, Texas, has occurred as a direct result of groundwater withdrawals for municipal supply, commercial and industrial use, and irrigation that depressured and dewatered the Chicot and Evangeline aquifers, thereby causing compaction of the aquifer sediments, mostly in the fine-grained silt and clay layers. This report, prepared by the U.S. Geological Survey in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, Lone Star Groundwater Conservation District, and Brazoria County Groundwater Conservation District, is one in an annual series of reports depicting water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers and measured cumulative compaction of subsurface sediments in the Chicot and Evangeline aquifers in the Houston-Galveston region. The report contains regional-scale maps depicting approximate 2015 water-level altitudes (represented by measurements made during December 2014–March 2015) for the Chicot, Evangeline, and Jasper aquifers; maps depicting 1-year (2014–15) water-level changes for each aquifer; maps depicting approximate contoured 5-year (2010–15) water-level changes for each aquifer; maps depicting approximate contoured long-term (1990–2015 and 1977–2015) water-level changes for the Chicot and Evangeline aquifers; a map depicting approximate contoured long-term (2000–15) water-level changes for the Jasper aquifer; a map depicting locations of borehole-extensometer sites; and graphs depicting measured cumulative compaction of subsurface sediments at the borehole extensometers during 1973–2014. Three tables listing the water-level data used to construct each water-level map for each aquifer and a table listing the measured cumulative compaction data for each extensometer site and graphs are included. In 2015, water-level-altitude contours for the Chicot aquifer ranged from 175 feet (ft) below the vertical datum (the National Geodetic Vertical Datum of 1929 or the North American Vertical Datum of 1988; hereinafter, datum) in a localized area in northwestern Harris County to 200 ft above datum in northern and western Montgomery County. Water-level changes for 2014–15 in the Chicot aquifer ranged from a 24-ft decline to a 31-ft rise. Contoured 5-year and long-term water-level changes in the Chicot aquifer ranged from a 40-ft decline to a 40-ft rise (2010–15), from a 100-ft decline to a 100-ft rise (1990–2015), and from a 100-ft decline to a 200-ft rise (1977–2015). In 2015, water-level-altitude contours for the Evangeline aquifer ranged from 250 ft below datum in a localized area extending from south-central Montgomery County into north-central Harris County and in an additional area located in central Harris County to 200 ft above datum in southeastern Grimes and northwestern Montgomery Counties. Water-level changes for 2014–15 in the Evangeline aquifer ranged from a 66-ft decline to a 78-ft rise. Contoured 5-year and long-term water-level changes in the Evangeline aquifer ranged from a 60-ft decline to an 80-ft rise (2010–15), from a 200-ft decline to a 240-ft rise (1990–2015), and from a 320-ft decline to a 240-ft rise (1977–2015). In 2015, water-level-altitude contours for the Jasper aquifer ranged from 200 ft below datum in south-central Montgomery County that extends into north-central Harris County to 250 ft above datum in northwestern Montgomery County. Water-level changes for 2014–15 in the Jasper aquifer ranged from a 17-ft decline to a 35-ft rise. Contoured 5-year and long-term water-level changes in the Jasper aquifer ranged from a 60-ft decline to four small, localized areas of 10-ft rises (2010–15) and from a 220-ft decline to no change (2000–15). Compaction of subsurface sediments (mostly in the fine-grained silt and clay layers) composing the Chicot and Evangeline aquifers was recorded continuously by using analog technology at the 13 borehole extensometers at 11 sites that were either activated or installed between 1973 and 1980. For the period of record beginning in 1973 (or later depending on activation or installation date) and ending in December 2014, measured cumulative compaction at the 13 extensometers ranged from 0.101 ft at the Texas City-Moses Lake extensometer to 3.668 ft at the Addicks extensometer. During 2014, a total of 10 of the 13 extensometers recorded a slight net decrease of land-surface elevation; the extensometers at the Lake Houston and Clear Lake (shallow) sites recorded slight net increases of land-surface elevation, and the extensometer at the Texas City-Moses Lake site recorded no change in elevation. The rate of compaction varies from site to site because of differences in rates of groundwater withdrawal in the areas adjacent to each extensometer site and differences among sites in the ratios of sand, silt, and clay and compressibilities of the subsurface sediments. It is not appropriate, therefore, to extrapolate or infer a rate of compaction for an adjacent area on the basis of the rate of compaction measured at nearby extensometers.

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USGS2014

Water-level altitudes 2014 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2013 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

Texas↗

USGS2013

Water-level altitudes 2013 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973--2012 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

Most of the subsidence in the Houston-Galveston region, Texas, has occurred as a direct result of groundwater withdrawals for municipal supply, commercial and industrial use, and irrigation that depressured and dewatered the Chicot and Evangeline aquifers, thereby causing compaction mostly in the clay and silt layers of the aquifer sediments. This report, prepared by the U.S. Geological Survey in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, Lone Star Groundwater Conservation District, and Brazoria County Groundwater Conservation District, is one in an annual series of reports depicting water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers and measured compaction of subsurface sediments in the Chicot and Evangeline aquifers in the Houston-Galveston region. The report contains maps depicting approximate water-level altitudes for 2013 (represented by measurements made during December 2012-February 2013) for the Chicot, Evangeline, and Jasper aquifers; maps depicting 1-year (2012-13) water-level changes for each aquifer; maps depicting 5-year (2008--13) water-level changes for each aquifer; maps depicting long-term (1990-2013 and 1977-2013) water-level changes for the Chicot and Evangeline aquifers; a map depicting long-term (2000-13) water-level changes for the Jasper aquifer; a map depicting locations of borehole-extensometer sites; and graphs depicting measured compaction of subsurface sediments at the extensometers during 1973-2012. Tables listing the data used to construct each water-level map for each aquifer and the compaction graphs are included. In 2013, water-level-altitude contours for the Chicot aquifer ranged from 200 feet (ft) below North American Vertical Datum of 1988 (hereinafter, datum) in a small area in southwestern Harris County to 200 ft above datum in central to west-central Montgomery County. Water-level changes during 2012-13 in the Chicot aquifer ranged from a 58-ft decline to a 37-ft rise. Contoured 5-year and long-term changes in water levels in the Chicot aquifer ranged from a 30-ft decline to an 80-ft rise (2008-13), from a 120-ft decline to a 100-ft rise (1990-2013), and from an 80-ft decline to a 200-ft rise (1977-2013). In 2013, water-level-altitude contours for the Evangeline aquifer ranged from 300 ft below datum in south-central Montgomery County to 200 ft above datum in southeastern Grimes and northwestern Montgomery Counties. Water-level changes for 2012-13 in the Evangeline aquifer ranged from a 37-ft decline to a 68-ft rise. Contoured 5-year and long-term changes in water levels in the Evangeline aquifer ranged from an 80-ft decline to an 80-ft rise (2008-13), from a 220-ft decline to a 220-ft rise (1990-2013), and from a 360-ft decline to a 260-ft rise (1977-2013). In 2013, water-level-altitude contours for the Jasper aquifer ranged from 200 ft below datum in south-central Montgomery and north-central Harris Counties to 250 ft above datum in northwestern Montgomery County and extending into northeastern Grimes and south-central Walker Counties. Water-level changes for 2012-13 in the Jasper aquifer ranged from a 36-ft decline to an 87-ft rise. Contoured changes in water levels in the Jasper aquifer ranged from a 100-ft decline to 20-ft rise (2008-13) and from a 220-ft decline to no change (2000-13). Compaction of subsurface sediments (mostly in the clay and silt layers) of the Chicot and Evangeline aquifers was recorded continuously by 13 borehole extensometers at 11 sites that were either activated or installed between 1973 and 1980. For the period of record beginning in 1973 (or later depending on activation or installation date) and ending in December 2012, cumulative measured compaction by 12 of the 13 extensometers ranged from 0.100 ft at the Texas City-Moses Lake extensometer to 3.632 ft at the Addicks extensometer (data were used from only one of two extensometers at one site). The rate of compaction varies from site to site because of differences in groundwater withdrawals near each site and differences among sites in the clay-to-sand ratio in the subsurface sediments. Therefore, it is not possible to extrapolate or infer a rate of compaction for adjacent areas based on the rate of compaction measured at a nearby extensometer.

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USGS2013

Groundwater withdrawals 1976, 1990, and 2000--10 and land-surface-elevation changes 2000--10 in Harris, Galveston, Fort Bend, Montgomery, and Brazoria Counties, Texas

The study area comprising Harris County and parts of Galveston, Fort Bend, Montgomery, and Brazoria Counties in southeastern Texas forms part of one of the largest areas of land-surface-elevation change in the United States. Land-surface-elevation change in the study area primarily is caused by the withdrawal of groundwater. Groundwater withdrawn from the Chicot and Evangeline aquifers has been the primary source of water for municipal supply, industrial and commercial use, and irrigation in the study area. Groundwater withdrawals cause compaction of clay and silt layers abundant in the aquifers, which has in turn resulted in the widespread, substantial land-surface-elevation changes in the region with increased flooding. To estimate land-surface-elevation changes, the U.S. Geological Survey (USGS), in cooperation with the Harris-Galveston Subsidence District (HGSD), documented land-surface-elevation changes in the study area that occurred during 2000–10 and 2005–10 based on elevation data measured by 11 USGS borehole-extensometer sites, a National Geodetic Survey Continuously Operating Reference Station, and Global Positioning System Port-A-Measure (PAM) sites operated by the HGSD and the Fort Bend Subsidence District. Groundwater withdrawals in the study area also were documented for 1976, 1990, and 2000–10. In 1976, about 428.9 million gallons per day (Mgal/d) were withdrawn from the aquifer system in Harris County, but by 2000, because of HGSD regulation, withdrawals had decreased to about 337.8 Mgal/d, or about a 21-percent reduction since 1976. By 2010, withdrawals had decreased to about 227.1 Mgal/d, or about a 47-percent reduction since 1976. Among the counties in the study area, the largest decrease in groundwater withdrawals has occurred in Galveston County since 1976. In 1976, about 27.4 Mgal/d were withdrawn from the aquifer system, and by 2000, withdrawals had decreased to about 4.12 Mgal/d, or about an 85-percent reduction since 1976. By 2010, withdrawals had decreased to about 0.626 Mgal/d, or about a 98-percent decrease since 1976. Since the mid-1970s, Fort Bend and Montgomery Counties have undergone extensive urban development and corresponding large increases in groundwater withdrawals. Total groundwater withdrawal for Fort Bend County in 1976 was about 16.0 Mgal/d, and by 2000, withdrawals had increased to about 86.5 Mgal/d, or about a 441-percent increase since 1976. By 2010, withdrawals in Fort Bend County had increased to about 99.8 Mgal/d, or about a 524-percent increase since 1976. Total groundwater withdrawal for Montgomery County in 1976 was about 7.84 Mgal/d, and by 2000, withdrawals had increased to about 43.6 Mgal/d, or about a 456-percent increase since 1976. By 2010, withdrawals in Montgomery County had increased to about 64.2 Mgal/d, or about a 719-percent increase since 1976. Total groundwater withdrawal in Brazoria County in 1976 was about 18.0 Mgal/d, and by 2000, withdrawals had increased to about 26.0 Mgal/d, or about a 44-percent increase. By 2010, withdrawals in Brazoria County had increased to about 24.7 Mgal/d, or about a 37-percent increase since 1976. Measured land-surface-elevation changes from December 31, 2000, to December 31, 2010, ranged from an elevation increase of 0.06 feet (ft), or an average increase in elevation of 0.006 ft per year, at the Seabrook borehole extensometer located near Seabrook, Tex., to an elevation decrease of 1.28 ft, or an average decrease in elevation of 0.128 ft per year, at a PAM station north of Jersey Village, Tex. (PAM 07). Measured land-surface-elevation changes from December 31, 2005, to December 31, 2010, ranged from an elevation increase of 0.07 ft, or an average increase in elevation of 0.014 ft per year, at PAM 09 in far northeastern Harris County to an elevation decrease of 0.51 ft, or an average decrease in elevation of 0.102 ft per year, at PAM 07.

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USGS2012

Water-level altitudes 2012 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2011 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

Most of the subsidence in the Houston–Galveston region, Texas, has occurred as a direct result of groundwater withdrawals for municipal supply, commercial and industrial use, and irrigation that depressured and dewatered the Chicot and Evangeline aquifers and caused compaction of the clay layers of the aquifer sediments. This report—prepared by the U.S. Geological Survey in cooperation with the Harris– Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, Lone Star Groundwater Conservation District, and Brazoria County Groundwater Conservation District—is one in an annual series of reports depicting water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction in the Chicot and Evangeline aquifers in the Houston–Galveston region. The report contains maps showing approximate water-level altitudes for 2012 (calculated from measurements of water levels in wells made during December 2011–February 2012) for the Chicot, Evangeline, and Jasper aquifers; maps showing 1-year (2011–12) water-level-altitude changes for each aquifer; maps showing 5-year (2007–12) water-levelaltitude changes for each aquifer; maps showing long-term (1990–2012 and 1977–2012) water-level-altitude changes for the Chicot and Evangeline aquifers; a map showing long-term (2000–12) water-level-altitude change for the Jasper aquifer; a map showing locations of borehole extensometer sites; and graphs showing measured compaction of subsurface sediments at the extensometers from 1973 (or later) through 2011. Tables listing the data that were used to construct each water-level map for each aquifer and the cumulative compaction graphs are included. In 2012, water-level-altitude contours for the Chicot aquifer ranged from 250 feet (ft) below North American Vertical Datum of 1988 (hereinafter, datum) in a small area in southwestern Harris County to 200 ft above datum in westerncentral Montgomery County. Water-level-altitude changes during 2012 in the Chicot aquifer ranged from a 48-ft decline to an 18-ft rise. Contoured 5-year and long-term changes in water-level altitudes in the Chicot aquifer ranged from a 60-ft decline to a 40-ft rise (2007–12), from a 100-ft decline to an 80-ft rise (1990–2012), and from a 100-ft decline to a 200-ft rise (1977–2012). In 2012, water-level-altitude contours for the Evangeline aquifer ranged from 300 ft below datum in isolated areas located in south-central Montgomery County and north-central Harris County, in southwest Harris County, and in northeastern Fort Bend County to 200 ft above datum near the county boundary intersection of Waller, Montgomery, and Grimes Counties. Water-level-altitude changes for 2012 in the Evangeline aquifer ranged from a 90-ft decline to a 39-ft rise. Contoured 5-year and long-term changes in waterlevel altitudes in the Evangeline aquifer ranged from an 80-ft decline to an 80-ft rise (2007–12), from a 220-ft decline to a 220-ft rise (1990–2012), and from a 360-ft decline to a 260-ft rise (1977–2012). In 2012, water-level-altitude contours for the Jasper aquifer ranged from 250 ft below datum in south-central Montgomery County to 250 ft above datum in northwest Montgomery County. Water-level-altitude changes for 2012 in the Jasper aquifer ranged from a 74-ft decline to a 4-ft rise. Contoured changes in water-level altitudes in the Jasper aquifer ranged from a 120-ft decline to no change (2007–12), and from a 220-ft decline to no change (2000–12). Compaction of subsurface sediments (mostly in the clay layers) composing the Chicot and Evangeline aquifers was recorded continuously at 13 borehole extensometers at 11 sites. For the period of record beginning in 1973 (or later) and ending in December 2011, cumulative compaction data collected from the 13 extensometers ranged from 0.102 ft at the Texas City–Moses Lake site to 3.621 ft at the Addicks site. The rate of compaction varies from site to site because of differences in groundwater withdrawals near each site and differences among sites in the clay-to-sand ratio in the subsurface sediments. Therefore, it is not possible to extrapolate or infer a rate of compaction for adjacent areas on the basis of the rate of compaction measured at a nearby extensometer.

Texas↗

USGS2012

Hydrogeology and simulation of groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system, Texas, 1891-2009

In cooperation with the Harris–Galveston Subsidence District, Fort Bend Subsidence District, and Lone Star Groundwater Conservation District, the U.S. Geological Survey developed and calibrated the Houston Area Groundwater Model (HAGM), which simulates groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system in Texas from predevelopment (before 1891) through 2009. Withdrawal of groundwater since development of the aquifer system has resulted in potentiometric surface (hydraulic head, or head) declines in the Gulf Coast aquifer system and land-surface subsidence (primarily in the Houston area) from depressurization and compaction of clay layers interbedded in the aquifer sediments. The MODFLOW-2000 groundwater flow model described in this report comprises four layers, one for each of the hydrogeologic units of the aquifer system except the Catahoula confining system, the assumed no-flow base of the system. The HAGM is composed of 137 rows and 245 columns of 1-square-mile grid cells with lateral no-flow boundaries at the extent of each hydrogeologic unit to the northwest, at groundwater divides associated with large rivers to the southwest and northeast, and at the downdip limit of freshwater to the southeast. The model was calibrated within the specified criteria by using trial-and-error adjustment of selected model-input data in a series of transient simulations until the model output (potentiometric surfaces, land-surface subsidence, and selected water-budget components) acceptably reproduced field measured (or estimated) aquifer responses including water level and subsidence. The HAGM-simulated subsidence generally compared well to 26 Predictions Relating Effective Stress to Subsidence (PRESS) models in Harris, Galveston, and Fort Bend Counties. Simulated HAGM results indicate that as much as 10 feet (ft) of subsidence has occurred in southeastern Harris County. Measured subsidence and model results indicate that a larger geographic area encompassing this area of maximum subsidence and much of central to southeastern Harris County has subsided at least 6 ft. For the western part of the study area, the HAGM simulated as much as 3 ft of subsidence in Wharton, Jackson, and Matagorda Counties. For the eastern part of the study area, the HAGM simulated as much as 3 ft of subsidence at the boundary of Hardin and Jasper Counties. Additionally, in the southeastern part of the study area in Orange County, the HAGM simulated as much as 3 ft of subsidence. Measured subsidence for these areas in the western and eastern parts of the HAGM has not been documented.

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USGS2012

Investigation of land subsidence in the Houston-Galveston region of Texas by using the Global Positioning System and interferometric synthetic aperture radar, 1993-2000

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.

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USGS2011

Water-level altitudes 2011 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2010 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

Most of the subsidence in the Houston–Galveston region has occurred as a direct result of groundwater withdrawals for municipal supply, industrial use, and irrigation that depressured and dewatered the Chicot and Evangeline aquifers causing compaction of the clay layers of the aquifer sediments. This report, prepared by the U.S. Geological Survey, in cooperation with the Harris–Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, and Lone Star Groundwater Conservation District, is one in an annual series of reports depicting water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction in the Chicot and Evangeline aquifers in the Houston–Galveston region. The report contains maps showing 2011 water-level altitudes for the Chicot, Evangeline, and Jasper aquifers; maps showing 1-year (2010–11) water-level-altitude changes for each aquifer; maps showing 5-year (2006–11) water-level-altitude changes for each aquifer; maps showing long-term (1990–2011 and 1977–2011) water-level-altitude changes for the Chicot and Evangeline aquifers; a map showing long-term (2000–11) water-level-altitude change for the Jasper aquifer; a map showing locations of borehole extensometer sites; and graphs showing measured compaction of subsurface material at the extensometers from 1973, or later, through 2010. Tables listing the data used to construct each aquifer-data map and the compaction graphs are included. Water levels in the Chicot, Evangeline, and Jasper aquifers were measured during December 2010–February 2011. In 2011, water-level-altitude contours for the Chicot aquifer ranged from 200 feet below North American Vertical Datum of 1988 (hereinafter, datum) in a small area in southwestern Harris County to 200 feet above datum in central to southwestern Montgomery County. Water-level-altitude changes in the Chicot aquifer ranged from a 40-foot decline to a 33-foot rise (2010–11), from a 10-foot decline to an 80-foot rise (2006–11), from a 140-foot decline to a 100-foot rise (1990–2011), and from a 120-foot decline to a 200-foot rise (1977–2011). In 2011, water-level-altitude contours for the Evangeline aquifer ranged from 300 feet below datum in north-central Harris County to 200 feet above datum at the boundary of Waller, Montgomery, and Grimes Counties. Water-level-altitude changes in the Evangeline aquifer ranged from a 43-foot decline to a 73-foot rise (2010–11), from a 40-foot decline to a 160-foot rise (2006–11), from a 200-foot decline to a 240-foot rise (1990–2011), and from a 340-foot decline to a 260-foot rise (1977–2011). In 2011, water-level-altitude contours for the Jasper aquifer ranged from 200 feet below datum in south-central Montgomery County to 250 feet above datum in east-central Grimes County. Water-level-altitude changes in the Jasper aquifer ranged from a 45-foot decline to a 29-foot rise (2010–11), from a 90-foot decline to a 10-foot rise (2006–11), and from a 190-foot decline to no change (2000–11). Compaction of subsurface materials (mostly in the clay layers) composing the Chicot and Evangeline aquifers was recorded continuously at 13 borehole extensometers at 11 sites. For the period of record beginning in 1973, or later, and ending in December 2010, cumulative clay compaction data measured by 12 extensometers ranged from 0.100 foot at the Texas City–Moses Lake site to 3.544 foot at the Addicks site. The rate of compaction varies from site to site because of differences in groundwater withdrawals near each site and differences among sites in the clay-to-sand ratio in the subsurface materials. Therefore, it is not possible to extrapolate or infer a rate of clay compaction for an area based on the rate of compaction measured at a nearby extensometer.

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USGS2010

Water-level altitudes 2010 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2009 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

Most of the subsidence in the Houston-Galveston region has occurred as a direct result of groundwater withdrawals for municipal supply, industrial use, and irrigation that depressured and dewatered the Chicot and Evangeline aquifers causing compaction of the clay layers of the aquifer sediments. This report, prepared by the U.S. Geological Survey, in cooperation with the Harris-Galveston Subsidence District, City of Houston, Fort Bend Subsidence District, and Lone Star Groundwater Conservation District, is one in an annual series of reports depicting water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction in the Chicot and Evangeline aquifers in the Houston-Galveston region. The report contains maps showing 2010 water-level altitudes for the Chicot, Evangeline, and Jasper aquifers, respectively; maps showing 1-year (2009-10) water-level-altitude changes for each aquifer; maps showing 5-year (2005-10) water-level-altitude changes for each aquifer; maps showing long-term (1990-2010 and 1977-2010) water-level-altitude changes for the Chicot and Evangeline aquifers; a map showing long-term (2000-10) water-level-altitude change for the Jasper aquifer; a map showing locations of borehole extensometer sites; and graphs showing measured compaction of subsurface material at the extensometers from 1973, or later, through 2009. Tables listing the data used to construct each aquifer-data map and the compaction graphs are included. Water levels in the Chicot, Evangeline, and Jasper aquifers were measured during December 2009-March 2010. In 2010, water-level-altitude contours for the Chicot aquifer ranged from 200 feet below National Geodetic Vertical Datum of 1929 or North American Vertical Datum of 1988 (hereinafter, datum) in a small area in southwestern Harris County to 200 feet above datum in central to southwestern Montgomery County. Water-level-altitude changes in the Chicot aquifer ranged from a 49-foot decline to a 67-foot rise (2009-10), from a 25-foot decline to a 35-foot rise (2005-10), from a 40-foot decline to an 80-foot rise (1990-2010), and from a 140-foot decline to a 200-foot rise (1977-2010). In 2010, water-level-altitude contours for the Evangeline aquifer ranged from 300 feet below datum in north-central Harris County to 200 feet above datum at the boundary of Waller, Montgomery, and Grimes Counties. Water-level-altitude changes in the Evangeline aquifer ranged from a 58-foot decline to a 69-foot rise (2009-10), from an 80-foot decline to an 80-foot rise (2005-10), from a 200-foot decline to a 220-foot rise (1990-2010), and from a 320-foot decline to a 220-foot rise (1977-2010). In 2010, water-level-altitude contours for the Jasper aquifer ranged from 200 feet below datum in south-central Montgomery County to 250 feet above datum in eastern-central Grimes County. Water-level-altitude changes in the Jasper aquifer ranged from a 39-foot decline to a 39-foot rise (2009-10), from a 110-foot decline to no change (2005-10), and from a 180-foot decline to no change (2000-10). Compaction of subsurface materials (mostly in the clay layers) composing the Chicot and Evangeline aquifers was recorded continuously at 13 borehole extensometers at 11 sites. For the period of record beginning in 1973, or later, and ending in December 2009, cumulative clay compaction data measured by 12 extensometers ranged from 0.088 foot at the Texas City-Moses Lake site to 3.559 foot at the Addicks site. The rate of compaction varies from site to site because of differences in groundwater withdrawals near each site and differences among sites in the clay-to-sand ratio in the subsurface materials. Therefore, it is not possible to extrapolate or infer a rate of clay compaction for an area based on the rate of compaction measured at a nearby extensometer.

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USGS2009

Water-level altitudes 2009 and water-level changes in the Chicot, Evangeline, and Jasper Aquifers and compaction 1973-2008 in the Chicot and Evangeline Aquifers, Houston-Galveston Region, Texas

This report, done in cooperation with the Harris-Galveston Subsidence District, the City of Houston, the Fort Bend Subsidence District, and the Lone Star Groundwater Conservation District, is one in an annual series of reports that depicts water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers, and compaction in the Chicot and Evangeline aquifers in the Houston-Galveston region, Texas. The report (excluding appendixes) contains 16 sheets and 15 tables: 3 sheets are maps showing current-year (2009) water-level altitudes for each aquifer, respectively; 3 sheets are maps showing 1-year (2008-09) water-level changes for each aquifer, respectively; 3 sheets are maps showing 5-year (2004-09) water-level changes for each aquifer, respectively; 4 sheets are maps showing long-term (1990-2009 and 1977-2009) water-level changes for the Chicot and Evangeline aquifers, respectively; 1 sheet is a map showing long-term (2000-2009) water-level change for the Jasper aquifer; 1 sheet is a map showing site locations of borehole extensometers; and 1 sheet comprises graphs showing measured compaction of subsurface material at the sites from 1973 or later through 2008, respectively. Tables listing the data used to construct the aquifer-data maps and the compaction graphs are included.

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USGS2009

Estimated land-surface subsidence in Harris County, Texas, 1915-17 to 2001

Land-surface subsidence, or land subsidence, in Harris County, Texas, which encompasses much of the Houston area, has been occurring for decades. Land subsidence has increased the frequency and extent of flooding, damaged buildings and transportation infrastructure, and caused adverse environmental effects. The primary cause of land subsidence in the Houston area is withdrawal of groundwater, although extraction of oil and gas also has contributed. Throughout most of the 20th century, groundwater was the primary source of municipal, agricultural, and industrial water supply for Harris County. Currently (2009) a transition to surface water as the primary source of supply, guided by a groundwater regulatory plan developed by the Harris-Galveston Subsidence District (2001), is in effect. The aquifers in Harris County contain an abundant amount of potable groundwater, but they also contain layers of clay. Groundwater withdrawals caused compaction of the clay layers, which in turn resulted in the widespread, substantial land-surface subsidence that has occurred in the Houston area.

Scientific Investigations Map↗

USGS2008

Water-level altitudes 2008 and water-level changes in the Chicot, Evangeline, and Jasper Aquifers and compaction 1973-2007 in the Chicot and Evangeline Aquifers, Houston-Galveston Region, Texas

This report, done in cooperation with the Harris-Galveston Subsidence District, the City of Houston, the Fort Bend Subsidence District, and the Lone Star Groundwater Conservation District, is one in an annual series of reports that depicts water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers, and compaction in the Chicot and Evangeline aquifers in the Houston-Galveston region, Texas. The report contains 17 sheets and 16 tables: 3 sheets are maps showing current-year (2008) water-level altitudes for each aquifer, respectively; 3 sheets are maps showing 1-year (2007-08) water-level changes for each aquifer, respectively; 3 sheets are maps showing 5-year (2003-08) water-level changes for each aquifer, respectively; 4 sheets are maps showing long-term (1990-2008 and 1977-2008) water-level changes for the Chicot and Evangeline aquifers, respectively; 1 sheet is a map showing long-term (2000-2008) water-level change for the Jasper aquifer; 1 sheet is a revision of a previously published water-level-altitude map for the Jasper aquifer for 2003; 1 sheet is a map showing site locations of borehole extensometers; and 1 sheet comprises graphs showing measured compaction of subsurface material at the sites from 1973 or later through 2007, respectively. Tables listing the data used to construct the aquifer-data maps and the compaction graphs are included.

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USGS2007

Water-level altitudes 2007 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2006 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

This report, done in cooperation with the Harris-Galveston Subsidence District, the City of Houston, the Fort Bend Subsidence District, and the Lone Star Groundwater Conservation District, is one in an annual series of reports that depicts water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers, and compaction in the Chicot and Evangeline aquifers in the Houston-Galveston, Texas, region. The report contains 18 sheets and 17 tables: 3 sheets are maps showing current-year (2007) water-level altitudes for each aquifer, respectively; 3 sheets are maps showing 1-year (2006-07) water-level changes for each aquifer, respectively; 3 sheets are maps showing 5-year (2002-07) water-level changes for each aquifer, respectively; 4 sheets are maps showing long-term (1990-2007 and 1977-2007) water-level changes for the Chicot and Evangeline aquifers, respectively; 1 sheet is a map showing long-term (2000-2007) water-level change for the Jasper aquifer; 2 sheets are revisions of previously published water-level-altitude maps for the Jasper aquifer for 2000 and 2002, respectively; 1 sheet is a map showing site locations of borehole extensometers; and 1 sheet comprises graphs showing measured compaction of subsurface material at the sites from 1973 or later through 2006, respectively. Tables listing the data used to construct the aquifer-data maps and the compaction graphs also are included.

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USGS2006

Water-level altitudes 2006 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2005 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

This report is one in an annual series of reports that depicts water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers, and compaction in the Chicot and Evangeline aquifers in the Houston-Galveston region. The Houston-Galveston region comprises Harris, Galveston, Fort Bend, Waller, and Montgomery Counties and adjacent parts of Brazoria, Grimes, Walker, San Jacinto, Liberty, and Chambers Counties. The report was prepared in cooperation with the Harris-Galveston Coastal Subsidence District, the City of Houston, the Fort Bend Subsidence District, and the Lone Star Groundwater Conservation District. For the Chicot and Evangeline aquifers, maps show approximate water-level altitudes in 2006, water-level changes from 2005 to 2006, and approximate water-level changes from 2001 to 2006, from 1990 to 2006, and from 1977 to 2006 (figs. 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ). For the Jasper aquifer, maps show approximate water-level altitudes in 2006 and water-level changes from 2005 to 2006 and 2000 to 2006 (figs. 11 , 12 , 13 ). The report also contains a map showing borehole extensometer (well equipped with compaction monitor) site locations ( fig. 14 ) and graphs showing measured compaction of subsurface material at these sites from 1973 or later to 2005 ( fig. 15 ). The U.S. Geological Survey (USGS) has published annual reports of water-level altitudes and water-level changes for the Chicot and Evangeline aquifers in the Houston-Galveston region since 1979; and annual reports of same for the Fort Bend subregion (Fort Bend County and adjacent areas) since 1990. The USGS published its first water-level-altitude map for the Jasper aquifer in the greater Houston area (primarily Montgomery County) in 2001. The 2006 water-level-altitude and water-level-change maps for the three aquifers are included in this report.

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USGS2005

Water-level altitudes 2005 and water-level changes in the Chicot, Evangeline, and Jasper aquifers and compaction 1973-2004 in the Chicot and Evangeline aquifers, Houston-Galveston region, Texas

This report is one in an annual series of reports that depicts water-level altitudes and water-level changes in the Chicot, Evangeline, and Jasper aquifers, and compaction in the Chicot and Evangeline aquifers in the Houston-Galveston region. The Houston-Galveston region comprises Harris, Galveston, Fort Bend, Waller, and Montgomery Counties and adjacent parts of Brazoria, Grimes, Walker, San Jacinto, Liberty, and Chambers Counties. The report was prepared in cooperation with the Harris-Galveston Coastal Subsidence District, the City of Houston, the Fort Bend Subsidence District, and the Lone Star Groundwater Conservation District. For the Chicot and Evangeline aquifers, maps show approximate water-level altitudes in 2005, water-level changes from 2004 to 2005, and approximate water-level changes from 2000 to 2005, from 1990 to 2005, and from 1977 to 2005 (figs. 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , and 10 ). For the Jasper aquifer, maps show approximate water-level altitudes in 2005 and water-level changes from 2004 to 2005 and 2000 to 2005 (figs. 11 , 12 , and 13 ). The report also contains a map showing borehole extensometer (well equipped with compaction monitor) site locations ( fig. 14 ) and graphs showing measured compaction of subsurface material at these sites from 1973 or later to 2004 ( fig. 15 ). The U.S. Geological Survey (USGS) has published annual reports of water-level altitudes and water-level changes for the Chicot and Evangeline aquifers in the Houston-Galveston region since 1979; and annual reports of same for the Fort Bend subregion (Fort Bend County and adjacent areas) since 1990. The USGS published its first water-level-altitude map for the Jasper aquifer in the greater Houston area (primarily Montgomery County) in 2001. The 2005 water-level-altitude and water-level-change maps for the three aquifers are included in this report.

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USGS2005

Evaluation of ground-water flow and land-surface subsidence caused by hypothetical withdrawals in the northern part of the Gulf Coast Aquifer system, Texas

During 2003–04 the U.S. Geological Survey, in cooperation with the Texas Water Development Board (TWDB) and the Harris-Galveston Coastal Subsidence District (HGCSD), used the previously developed Northern Gulf Coast Ground-Water Availability Modeling (NGC GAM) model to evaluate the effects of hypothetical projected withdrawals on ground-water flow in the northern part of the Gulf Coast aquifer system and land-surface subsidence in the NGC GAM model area of Texas. The Gulf Coast aquifer system comprises, from the surface, the Chicot and Evangeline aquifers, the Burkeville confining unit, the Jasper aquifer, and the Catahoula confining unit. Two withdrawal scenarios were simulated. The first scenario comprises historical withdrawals from the aquifer system for 1891–2000 and hypothetical projected withdrawals for 2001–50 compiled by the TWDB (TWDB scenario). The projected withdrawals compiled by the TWDB are based on ground-water demands estimated by regional water planning groups. The second scenario is a “merge” of the TWDB scenario with an alternate set of projected withdrawals from the Chicot and Evangeline aquifers in the Houston metropolitan area for 1995–2030 provided by the HGCSD (HGCSD scenario). Under the TWDB scenario withdrawals from the entire system are projected to be about the same in 2050 as in 2000. The simulated potentiometric surfaces of the Chicot aquifer for 2010, 2020, 2030, 2040, and 2050 show relatively little change in configuration from the simulated 2000 potentiometric surface (maximum water-level depths in southern Harris County 150–200 feet below NGVD 29). The simulated decadal potentiometric surfaces of the Evangeline aquifer show the most change between 2000 and 2010. The area of water levels 250– 400 feet below NGVD 29 in western Harris County in 2000 shifts southeastward to southern Harris County, and water levels recover to 200–250 feet below NGVD 29 by 2010. Water levels in southern Harris County recover to 150–200 feet below NGVD 29 by 2020 and remain in that range through 2050. A relatively small cone of depression in southern Montgomery County that did not appear in the 2000 surface develops and enlarges during the projected period, with a maximum depth of 250–300 feet below NGVD 29 in 2030, 2040, and 2050. The simulated decadal potentiometric surfaces of the Jasper aquifer each have a major cone of depression centered in southern Montgomery County that was minimally developed in 2000 but reaches depths of 550–650 feet below NGVD 29 in the 2020, 2030, 2040, and 2050 surfaces. Under the TWDB scenario the percentage of withdrawals supplied by net recharge increases from 75 percent in 2000 to 87 percent in 2050, and the percentage of withdrawals supplied by storage decreases from 25 percent in 2000 to 13 percent in 2050. Under the HGCSD scenario, withdrawals from the Chicot and Evangeline aquifers increase about 74 percent during 1995–2030; Jasper aquifer withdrawals are unchanged from those of the TWDB scenario. For the 2010, 2020, and 2030 potentiometric surfaces of the Chicot and Evangeline aquifers, the substantially greater withdrawals of the HGCSD scenario relative to those of the TWDB scenario result in progressively deeper cones of depression than those in the potentiometric surfaces associated with the TWDB scenario—for the Chicot aquifer in southern Harris County, 400–450 feet below NGVD 29 in 2030; for the Evangeline aquifer in southern Montgomery County, 700–750 feet below NGVD 29 in 2030. Although Jasper aquifer withdrawals are the same for both scenarios, the major cone of depression centered in southern Montgomery County in the 2030 potentiometric surface is 50 feet deeper at its center (600–700 feet below NGVD 29) than the cone in the 2030 surface under the TWDB scenario. Under the HGCSD scenario, the percentage of withdrawals supplied by net recharge decreases from 72 percent in 1995 to 57 percent in 2030, and the percentage of withdrawals supplied by storage increases from 28 percent in 2000 to 43 percent in 2030. About 85 percent of the increase supplied by storage is from the compaction of clay. Land-surface subsidence in the major area of subsidence centered in Harris and Galveston Counties during 2000–50 that results from simulating the TWDB withdrawal scenario expands slightly to the west and increases in places. The maximum change occurs in the Conroe area where subsidence increases from about 4 to about 13 feet during the projected period. Land-surface subsidence in the major area of subsidence during 1995–2030 that results from simulating the HGCSD withdrawal scenario increases substantially. For example, in east-central Harris County maximum subsidence increases from about 10–11 feet in 1995 to 22 feet in 2030. The hypothetical projected withdrawal scenarios are estimates of future withdrawals and might not represent actual future withdrawals. The simplifying assumptions that the downdip limit of freshwater flow in each hydrogeologic unit is a stable, sharp interface across which no flow occurs and that the base of the system is a no-flow boundary become less realistic and thus increase the uncertainty in results as drawdowns increase. The presence of uncertainty dictates that the results of the predictive simulations described in this report be used with caution in any decision-making process.

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