Get 20M+ Full-Text Papers For Less Than $1.50/day. Subscribe now for You or Your Team.

Learn More →

Land subsidence and aquifer compaction in Montgomery County, Texas, U.S.: 2000–2020

Land subsidence and aquifer compaction in Montgomery County, Texas, U.S.: 2000–2020 Groundwater-withdrawal-induced land subsidence has been a big concern in Montgomery County, Texas, U.S. since the 2000s. As of 2020, approximately half of the entire county is experiencing subsidence over 5 mm/year. This study aims to investigate ongoing land subsidence in Montgomery County using groundwater-level, extensometer, and GPS datasets. According to this study, land subsidence in Montgomery County since the mid-2000s is primar- ily contributed by sediment compaction in the Evangeline and Jasper aquifers; the compaction of Jasper aquifer contributes approximately one-third of the land subsidence since the mid-2000s; the pre-consolidation heads of the Chicot, Evangeline, and Jasper aquifers in Montgomery County are close to each other, approximately 15–25 m below mean sea level; the virgin-compaction/head-decline ratio is approximately 1:250 in the Evangeline aquifer and 1:800 in the Jasper aquifer in central and southern Montgomery County. As of 2020, the Jasper groundwater-level altitude is approximately 20–40 m below the pre-consolidation head in the central and southern Montgomery County; the Evangeline groundwater-level altitude is about 40–60 m below the pre-consolidation head. Land subsidence will con- tinue to occur as long as the groundwater-level altitude in either the Evangeline or the Jasper aquifer remains below the pre-consolidation head. Keywords: Subsidence, Pumping, GPS, Pre-consolidation head, Virgin-compaction/head-decline ratio Introduction 2015; Petersen et al. 2020). The Woodlands in Montgom - Study area ery County has become one of the most affected areas by Montgomery County is a part of the Houston–The subsidence in the Greater Houston region since the 2010s Woodlands–Sugar Land, Texas Metropolitan Statistical (Fig. 1). Area (MSA), which is often designated as Greater Hou- Montgomery County comprises approximately ston, encompassing nine counties along the Gulf Coast 2700  km of flat to gently rolling terrain, with eleva - in Southeast Texas with a population of over seven mil- tions ranging from about 40–120  m above sea level. lion people at the 2020 census estimates (Fig.  1). Land Groundwater-withdrawal-induced land subsidence subsidence has affected the Greater Houston region for was reported in southern Montgomery County in the nearly a century. As the population has grown outward early 1960s (Gabrysch 1967). Land surface deformation from Houston to the north and the northwest since the monitoring using Global Positioning System (GPS) in 1990s, groundwater pumping, in turn, land subsidence, Montgomery County began in the early 2000s. Rapid follows the same pattern of urban expansion (e.g., Cop- subsidence up to 20  mm/year was recorded by GPS in lin and Galloway 1999; Qu et al. 2015; Turco and Petrov northern Harris County and southern Montgomery County during the 2000s (e.g., Welch 2018; Zhou 2020). The ongoing land subsidence since the mid-2010s is approximately 5–7  mm/year in central Montgom- *Correspondence: gwang@uh.edu Department of Earth and Atmospheric Sciences, University of Houston, ery County and 8–10  mm/year in southern Mont- Houston 77204, USA gomery County. Over half of Montgomery County is Full list of author information is available at the end of the article © The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Wang et al. Geoenviron Disasters (2021) 8:28 Page 2 of 24 Fig. 1 Map showing the contours of average subsidence rates (2016–2020) derived from over 210 permanent GPS observations (> 3 years) within the Greater Houston region. The gray squares represent GPS sites used for creating the contour map. The subsidence rates are aligned to the Stable Houston Reference Frame (Houston20). The northwest corner of this map displays outcrops of the Gulf Coast Aquifer (Casarez 2020). The color patterns represent the areas regulated by the Harris-Galveston Subsidence District (HGSD: Areas 1, 2, 3), the Fort Bend Subsidence District (FBSD: Areas A and B), the Brazoria County Groundwater Conservation District (BCGCD), and the Lone Star Groundwater Conservation District (LSGCD) experiencing land subsidence over 5  mm/year as of Local aquifers 2020 (Fig. 1). In Montgomery County, the principal source of usable Ground deformation associated with subsidence and groundwater is the Gulf Coast Aquifer, which comprises faulting has caused frequent damages to residential five subdivisions in and around Montgomery County: buildings and public infrastructure in northern Harris from shallowest to deepest, the Chicot aquifer, the Evan- County and southern Montgomery County (e.g., Khan geline aquifer, the Burkeville confining unit, the Jas - et al. 2013; Campbell et al. 2018; Qu et al. 2019). Long- per aquifer, and the Catahoula Sandstone (Baker 1979; term subsidence also increases the flooding risk (e.g., Chowdhury and Turco 2006). These subdivisions crop Miller and Shirzaei 2019), which has a particular con- out in northwestern Montgomery County, as depicted in cern in low-lying residential areas in southern Mont- Fig.  1, where the aquifers receive recharge from precipi- gomery County. tation and surface water (Kasmarek and Robinson 2004). W ang et al. Geoenviron Disasters (2021) 8:28 Page 3 of 24 The Chicot aquifer is the youngest of the Gulf Coast Figure  3 lists the history of groundwater and surface Aquifer subdivisions, followed by the Evangeline Aquifer, water use in Montgomery County from 1984 to 2018. the Burkeville confining unit, and the Jasper aquifer. The The data is from Texas Water Development Board Catahoula sandstone is the oldest of the Gulf Coast Aqui- (TWDB) Historical Water Use Estimates Database fer System. The successively older units crop out pro - ( h t t p :/ / w w w . t w d b . t e x a s . g o v / w a t e r p l a n n i n g / w a t e r u s e s u gressively further inland at higher elevations (Figs.  1, 2). rvey/ estim ates/ index. asp). Groundwater pumping These aquifers comprise laterally discontinuous gravel, gradually increased with the county’s growth in popula- sand, silt, and clay (Baker 1979). The thickness of the tion since the 1980s and reached the maximum in 2011 Chicot aquifer in Montgomery County varies from less (~ 125 × 10  m ). Total groundwater use increased by a than 100  m in the north to approximately 200  m in the factor of ten from approximately 13 × 10 m in 1984 to south; the thickness of the Evangeline aquifer is approxi- 130 × 10  m in 2011, with the vast majority (over 90%) mately 200  m; the thickness of the Burkeville confining of groundwater use going to the municipal sector. The system is about 100 m throughout the county; the thick- extraordinary groundwater pumping from 2011 to 2013 ness of the Jasper aquifer is around 300–500  m (Popkin was resulted by the severe drought occurred during this 1971; Young et al. 2012) (Fig. 2). period in the southern U.S. The Texas State Legislature established the Lone Star Groundwater use and management Groundwater Conservation District (LSGCD) in 2001 The Chicot, Evangeline, and the upper portion of Jasper to regulate groundwater use and control subsidence in aquifers generally contain freshwater throughout the Montgomery County. According to LSGCD’s pumping county. The lower part of the Jasper and Catahoula Sand - data associated with permits, the pumping amount from stone contain slightly saline water (brackish water) in the the Chicot aquifer was approximately 2–3% of the annual northern and central parts of the county (Popkin 1971). total-pumping during the past 2  decades; the pumping Fig. 2 Generalized hydrogeologic section of the Gulf Coast Aquifers crossing Montgomery County from the south to the north. The extension of the cross-profile is illustrated in Fig. 1 (white line). The depth and thickness information of the aquifers is combined from Popkin (1971), Baker (1979), and Young et al. (2012) Wang et al. Geoenviron Disasters (2021) 8:28 Page 4 of 24 Fig. 3 Groundwater and surface water use in Montgomery County from 1984 to 2018. The water use information is combined from the Texas Water Development Board ( TWDB)’s Water Use Database (http:// www. twdb. texas. gov/ water plann ing/ water usesu rvey/ estim ates/ index. asp) amount from the Evangeline aquifer was approximately level declined throughout the county before 2015, with 50–55% of the annual total-pumping, and the pump- the most rapid decline in southern Montgomery County. ing amount from the Jasper aquifer was approximately The decline rate was about 3 m/year in the area between 40–45% of the annual total-pumping (Thornhill and The Woodlands and Conroe. The 2015–2019 Jasper Keester 2020). groundwater-level-change contours reveal that ground- LSGCD has been continuously improving its Manage- water level was rising throughout the entire county since ment Plan since it was created in 2001. The original man - 2015. The rising rate in northern Conroe and eastern The agement plan was adopted on October 14, 2003, then Woodlands was about 2 m/year. later amended and re-adopted in 2008, in 2013, and most In August 2015, the City of Conroe and seven other recently in 2020. The 2013 management plan mandated utility providers filed a lawsuit against the LSGCD over large-volume groundwater users, such as the City of Con- the district’s regulations of groundwater usage. On roe and large water utilities, to reduce their groundwater May 17, 2019, the 284th District Court in Montgom- production by thirty percent (30%) of their Total Qualify- ery County signed a Final Judgment declaring that the ing Demand (approximately their total water use amount large-volume groundwater user rules under the LSGCD’s in 2009) by January 1, 2016 (LSGCD 2013). As part of a Regulatory Plan were adopted without legal authority groundwater usage reduction plan, the San Jacinto River and consequently are unenforceable. LSGCD adjusted Authority built a surface water treatment facility in Con- its groundwater regulation rules accordingly in 2020. The roe (https:// www. sjra. net/ grp/ treat ment- plant). It began LSGCD’s 2020 Regulatory Plan no longer requires the to transfer treated surface water from Lake Conroe to large-volume groundwater users to follow the previous the central and southern county areas in 2015. Before requirement of reducing their groundwater pumping by 2015, groundwater use was about 95% of the total water thirty percent of their Total Qualifying Demand (LSGCD in Montgomery County. As of 2018, the groundwater use 2020). has reduced to approximately 85% of the total water use (Fig. 3). Motivation The reduction in groundwater pumping since the mid- The Harris-Galveston Subsidence District (HGSD), 2010s has resulted in county-wide groundwater-level United State Geological Survey (USGS), LSGCD, and recovery in both the Evangeline and Jasper aquifers. several other local agencies have been conducting Figure  4 illustrates the groundwater-level contour lines groundwater-level and subsidence monitoring for over showing Jasper groundwater changes during 5  years 4 decades in northern Harris County and southern Mont- before and after 2015. The 2010–2014 Jasper groundwa - gomery County. Groundwater pumping in northern Har- ter-level-change contours reveal that the groundwater ris County is primarily from the Chicot and Evangeline W ang et al. Geoenviron Disasters (2021) 8:28 Page 5 of 24 Fig. 4 Jasper groundwater-level changes in Montgomery County. a The change of groundwater altitude during the 5-year period from the beginning of 2010 to the end of 2014; b the change of groundwater altitude in meters during the 5-year period from the beginning of 2015 to the end of 2019. The color bar indicates the magnitude of groundwater altitude changes in meters aquifers (Greuter and Petersen 2021). The correlation the research and groundwater management communi- between subsidence and groundwater level changes and ties: (1) has aquifer compaction extended to Jasper aqui- the compressibility of the Chicot and Evangeline aquifers fer in Montgomery County? (2) If yes, how much is the in Harris County have been deliberately investigated by contribution of the Jasper aquifer to the present land USGS (e.g., Kasmarek et al. 2016; Shah et al. 2018; Braun subsidence? (3) What is the compressibility of the Jasper and Ramage 2020). One important conclusion is that the aquifer? This investigation aims to address these ques - groundwater-withdrawal-induced sediment compaction tions using publicly-available groundwater-level, exten- has not extended to the Jasper aquifer, at least in central someter, and GPS datasets. and southern Harris County. In general, the compaction is limited within the Chicot aquifer and the top portion Data and methodology of the Evangeline aquifer, approximately within 600 m to GPS data the ground surface (Yu et al. 2014). However, groundwa- The Greater Houston region is one of the earliest ter pumping in Montgomery County is primarily from urban areas to employ GPS technology for land sub- the Evangeline and Jasper aquifers. The percentage of sidence and fault monitoring. As of 2021, HGSD and Jasper groundwater pumping among total groundwa- the University of Houston (UH) have integrated over ter pumping has been gradually increasing since the 240 permanent GPS stations into their routine GPS 2010s. The upper portion of the Jasper aquifer is desig - data processing for land subsidence monitoring in the nated as the primary target for fresh water in northern Greater Houston region, approximately 2.2 × 10  km Harris County and southern Montgomery County, and (Fig. 1). There are 14 permanent GPS stations with over the lower portion of the Jasper aquifer is designated as 5-year observational history in Montgomery County as potential sources of brackish groundwater (e.g., Young of 2020 (Fig. 5). HGSD installed a new permanent GPS et  al. 2016; Kelley et al. 2018). The confined zones of the station, YORS, in the south of The Woodlands in 2020, Jasper and Evangeline aquifers retain the highest risk for in cooperation with The Woodlands Water Agency and future subsidence from pumping (Furnans et  al. 2018). the San Jacinto River Authority. P013, P012, P068, P070, There is a general lack of understanding regarding the P071, and P073 are campaign-style permanent GPS sta- compressibility and potential compaction for the Jasper tions, also known as Port-A-Measure (PAM) stations, Aquifer. Following questions have been raised in both operated by HGSD in cooperation with LSGCD. These Wang et al. Geoenviron Disasters (2021) 8:28 Page 6 of 24 Fig. 5 Map showing the locations of GPS and groundwater-level observation wells in Montgomery County and adjacent areas. A letter is added to the end of USGS well ID. “C” represents a Chicot well. “E” represents an Evangeline well. “J” represents a Jasper well PAM stations were designed for periodically repeated Woodlands, the City of Conroe, the Northeast, and the long-term monitoring. On average, PAM data was col- Southwest (Fig. 5). lected for 1 week every month before 2005 and 1 week The raw data of PAM stations are archived at HGSD. per 2  months after 2005. TXCN is a Continuously The raw data of UH GPS are archived at UH and Operating Reference Station (CORS) operated by the UNAVCO. CORS raw data are archived at National Texas Department of Transportation (TxDOT, https:// Geodetic Survey (NGS) at the National Oceanic and w w w. t x dot . gov/ inside- t x dot/ div i s ion/ inf or ma tion- Atmospheric Administration (NOAA). GPS-derived sub- techn ology/ gps. html). UH02 is a CORS jointly operated sidence time series are open to the public through HGSD. by UH and SmartNet (https:// www. smart netna. com). The subsidence time series are obtained by differenc - UHF1, UHJF, PWES, GSEC, and WHCR are continu- ing the GPS-derived ellipsoidal heights with respect to ous GPS stations operated by UH. UHF1 and UHJF are the Stable Houston Reference Frame 2020, abbreviated closely-spaced. Only the observations at UHF1 are used as Houston20. Houston20 is realized by long-term GPS in this study. The detailed information of these GPS observations at 25 Continuously Operating Reference stations is listed in Table  1. The UH GPS network con - Stations (CORS) located outside of the greater Houston sists of over 70 permanent GPS stations in the Houston region, where no considerable groundwater-withdrawal- metropolitan region (Wang et  al. 2015). Four GPS sta- induced subsidence has occurred since the 1990s tions (P017, ROD1, COH6, P065) located in northern (Agudelo et al. 2020). Harris County, adjacent to Montgomery County, are The stability of Houston20 is at a level of 0.3 mm/year also investigated in this study. P017 and P065 are PAM in each horizontal direction (NS: North–South; EW: stations. COH6 is a CORS jointly operated by the City East–West) and 0.8  mm/year in the vertical direction. A of Houston and HGSD. ROD1 is a CORS operated by detailed GPS data process strategy is addressed in Wang RODS Surveying Inc. (http:// www. rods. cc). Based on et al. (2013) and Kearns et al. (2019). The accuracy (root the distribution of GPS stations, we have investigated mean square error) of daily vertical-positions derived the land subsidence in the following four areas: The from GPS observations is 6–8  mm (Wang et  al. 2017). W ang et al. Geoenviron Disasters (2021) 8:28 Page 7 of 24 Table 1 Permanent GPS stations in Montgomery County, Texas GPS Location Observational history Vertical displacement (negative indicates Raw data archiving subsidence) Latitude Longitude Start End Years Days Total (cm) 5-year rate Operator (cm/year) P012 − 95.263 30.060 2000.9 2020.4 19.5 1331 − 12.2 − 0.6 HGSD HGSD P013 − 95.490 30.195 2000.9 2021.2 20.3 1259 − 25.2 − 1.4 HGSD HGSD P068 − 95.587 30.185 2011.8 2021.2 9.4 545 − 8.9 − 1.0 HGSD HGSD P069 − 95.459 30.199 2011.7 2021.2 9.4 556 − 10.6 − 1.1 HGSD HGSD P070 − 95.424 30.291 2011.8 2021.2 9.5 493 − 4.9 − 0.5 HGSD HGSD P071 − 95.579 30.353 2011.8 2021.2 9.5 553 − 3.8 − 0.4 HGSD HGSD P072 − 95.242 30.147 2012.0 2021.2 9.2 398 − 7.5 − 0.7 HGSD HGSD YORS − 95.469 30.110 2020.8 2021.2 0.3 126 HGSD HGSD TXCN − 95.441 30.349 2005.6 2021.3 15.7 5707 − 17.2 − 1.2 TxDOT NGS UH02 − 95.457 30.315 2015.0 2021.2 6.2 2114 − 3.6 − 0.6 UH&SmartNet UH&UNAVCO UHF1/UHJF − 95.483 30.236 2014.4 2020.7 6.3 2258 − 5.9 − 0.6 UH UH&UNAVCO WHCR − 95.505 30.194 2014.8 2021.3 6.5 2363 − 3.7 − 0.6 UH UH&UNAVCO PWES − 95.511 30.199 2015.2 2021.3 6.0 2205 − 6.1 − 0.9 UH UH&UNAVCO GSEC − 95.528 30.197 2015.8 2021.3 5.5 2008 − 2.8 − 0.7 UH UH&UNAVCO Total subsidence represents the total vertical displacement over the entire history of each GPS station The 5-year subsidence rate represents the linear trend of the subsidence time series from 2016 to 2020 YORS is a new station installed in 2020. http:// www. twdb. texas. gov/ water plann ing/ water usesu rvey/ estim ates/ index. asp For subsidence studies, users often pay more attention to secular effects (e.g., Wang et  al. 2020; Zhou et  al. the accuracy or confidence of the estimated subsidence 2021). So, GPS-derived subsidence with respect to rates (linear trends) rather than the accuracy of individ- Houston20 is principally caused by local-scale anthro- ual positions. In general, longer GPS observations would pogenic processes, primarily the aquifer compaction result in higher accuracy for estimating subsidence rates. associated with groundwater withdrawals. According Wang (2021) provides an empirical formula for estimat- to the report of Texas Drilling (http:// www. texas- drill ing the 95% confidence interval (95% CI, also called accu -ing. com/ montg omery- county), the oil and gas pro- racy) of GPS-derived vertical site velocities: duction in Montgomery County has reduced signifi- cantly since the 2000s. So far, the exact magnitude of the contribution of hydrocarbon production is still b = 5.2 × , (1) 95%CI 1.25 uncertain and remains an important issue for future investigations. where T is the year range of the time series in decimal GPS-derived heights are the distances above a years and b is the 95% confidence interval of the 95%CI smooth ellipsoid surface, which are called ellipsoidal linear trend (b) in millimeters per year. According to the heights. Conventional subsidence obtained from lev- empirical formula, 4-year continuous GPS observations eling survey is a physical quantity that refers to the would result in a subsidence-rate estimate with an accu- surface of the geoid, called orthometric heights in racy (95%CI) of 1  mm/year; 7-year continuous observa- surveying engineering. Ellipsoidal heights and ortho- tions would result in a subsidence-rate estimate with an metric heights are essentially different. The former is a accuracy (95% CI) of 0.5 mm/year. geometric quantity, while the latter is a physical-based The realization of regional reference frames has quantity. According to Wang and Soler (2014), ellip- excluded or minimized the regional “common” ground soid heights and orthometric heights would result in movements, including the secular plate movement of the same practical subsidence measurements during the North American Plate with respect to the Inter- the same time span. Accordingly, the subsidence values national GNSS Service (IGS) reference frames, glacial provided in this study can be regarded as having the isostatic adjustment (GIA), natural consolidation of same physical meaning as the conventional subsidence young sediments, surface mass loading associated with measurements obtained from leveling surveys. atmosphere and ocean, and other regional-scale minor Wang et al. Geoenviron Disasters (2021) 8:28 Page 8 of 24 Groundwater data American Vertical Datum of 1988 (NAVD88). Since the Groundwater levels in Montgomery County, Texas, have altitude of the mean sea level is approximately equivalent been periodically measured since the 1940s. Records of to zero with respect to NAVD88, the NAVD88 altitude is these measurements, known as groundwater data or well also referred to as mean sea level or simply sea level in data, are routinely published by the TWDB and USGS. practice. In this article, the groundwater-level altitudes The groundwater-level observation data used for this below mean sea level and above mean sea level are here- study are downloaded from the USGS National Water after referred to as negative and positive, respectively. For Information System (NWIS) (https:// water data. usgs. gov/ example, the groundwater-level altitude at 40  m below nwis) (Ramage 2020). Groundwater-level data collection sea level is abbreviated as − 40 m; the groundwater-level methods, data quality, and the status of groundwater altitude at 40 m above sea level is abbreviated as 40 m. levels are addressed in the most recent USGS Scientific The earliest Chicot groundwater-level measurements Investigations Report 2020-5089 (Braun and Ramage are available back to the 1980s. In general, the Chicot 2020). As of 2020, the USGS groundwater datasets com- groundwater-level altitude at each well was stable dur- prise 11 Chicot wells, 81 Evangeline wells, 99 Jasper wells, ing the past 3–4 decades and above the pre-consolidation and 13 Catahoula wells in Montgomery County (Fig. 5). head of the Chicot aquifer (Fig.  6). Determination of the Chicot pre-consolidation will be explained in the fol- The Chicot groundwater level lowing sections. There is a general trend that the Chicot Figure 6 depicts the groundwater levels recorded by these groundwater level declines from the north to the south. 11 Chicot wells in Montgomery County during the past The stability of the Chicot groundwater levels can be 3  decades. In this article, the groundwater-level alti- explained by the fact that groundwater pumping in the tudes are aligned to the height with respect to the North Chicot aquifer is minor in Montgomery County, at least Fig. 6 Groundwater levels in 11 wells completed in the Chicot aquifer in Montgomery County. In the legend, “30194809529004 (− 24 m, 73 m)” indicates USGS well number, well depth below land surface (BLS), and the elevation of land surface reference to mean sea level (MSL). The locations of these wells are marked in Fig. 5 W ang et al. Geoenviron Disasters (2021) 8:28 Page 9 of 24 during the past 2  decades. As mentioned earlier, annual plotted in Fig. 5. The Jasper groundwater level in Conroe pumping volumes from the Chicot aquifer are approxi- (USGS ID: 301828095272404, completed 373  m below mately 2–3% of the annual total pumping in Montgom- land surface) was about 60 m in the 1960s and started to ery County since the 2000s. The highest pumping rates decline since the 1970s and reached the lowest altitude from the Chicot aquifer are in The Woodlands area. It is (− 50 m) in the early 2010s, then began to rise in the mid- unlikely that the compaction of the Chicot aquifer could 2010s as a result of the groundwater regulations enforced remarkably contribute to the ongoing land subsidence by LSGCD. The Evangeline groundwater level in the (total compaction). upper Woodlands area (USGS ID: 301516095264301, terminated 214 m below land surface) followed a similar Evangeline and Jasper groundwater levels pattern with the Jasper groundwater level. As of 2020, the Groundwater-level monitoring in Montgomery County lowest groundwater-level altitudes in the Chicot, Evange- began as early as the 1940s in the Jasper aquifer and the line, and Jasper aquifers are − 10 m, − 80 m, and − 60 m, 1960s in the Evangeline aquifer. Figure  7 illustrates the respectively, in southern Montgomery County (Fig. 7). long-history groundwater-level changes in the Chicot Figure 8 depicts the contours of groundwater-level alti- aquifer (1989–2020), the Evangeline aquifer (1964–2020), tudes as of the beginning of 2020 in the Evangeline and and the Jasper aquifer (1956–2020). Groundwater-level Jasper aquifers in Montgomery County. The base contour changes at three wells with the lowest altitudes as of line (− 15  m) represents the pre-consolidation head of 2020 in the Chicot, Evangeline, and Jasper aquifer are each aquifer. The Jasper pre-consolidation-head is coinci - also illustrated in Fig.  7. The locations of these wells are dent with the 5-mm/year subsidence contour. The Jasper Fig. 7 The multi-decadal history of the Chicot, Evangeline, and Jasper groundwater levels in Montgomery County. Open symbols: groundwater-level changes at three long-history wells completed in the Chicot (1989–2020), Evangeline (1964–2020), and Jasper aquifers (1956–2020). Filled symbols: groundwater-level changes at three wells remaining the lowest altitude as of 2020 in the Chicot, Evangeline, and Jasper aquifers. Evangeline and Jasper groundwater levels began to rise in 2015 as a result of the reduction of pumping Wang et al. Geoenviron Disasters (2021) 8:28 Page 10 of 24 Fig. 8 Evangeline (blue) and Jasper (red) groundwater-level contours as of the beginning of 2020 in Montgomery County. Groundwater-level altitudes are referenced to the mean sea level (zero meters) defined by the North American Vertical Datum of 1988 (NAVD88). The base contour lines (− 15 m) represent the pre-consolidation heads in the Evangeline aquifer (blue) and the Jasper aquifer (red). The white dashed line represents the 5 mm/year subsidence-contour-line illustrated in Fig. 1 groundwater-level altitude in central and southern Mont- The Lake Houston site is approximately 17  km south gomery County, approximately half of the entire county of Montgomery County. Groundwater levels at the area, is below the pre-consolidation head. A groundwater Lake Houston site will be addressed in the next sec- decline bowl is occurring in The Woodlands area within tion. Since there is little groundwater pumping from both the Evangeline and Jasper aquifers. The Jasper the Burkeville confining unit and the groundwater level groundwater-level altitudes are about − 50  m to − 70  m remained stable during the past decades, no consider- in The Woodlands area, and the Evangeline groundwater- able compaction associated with groundwater pumping level altitude are about from − 60 to − 80 m. is expected in this unit. The pumping from the Catahoula sandstone started in the early 2010s and gradually increased. As of 2018, Groundwater levels in Burkeville confining unit the pumping amount from the Catahoula sandstone was and Catahoula sandstone below 5% of the annual total-pumping in Montgomery The Burkeville confining unit consists primarily of clay, County (Thornhill and Keester 2020). USGS began to which restricts the water flow from the Evangeline monitor groundwater-level in the Catahoula sandstone aquifer to the Jasper aquifer. There are no groundwa - in 2011. There are 13 groundwater-level observation ter-level measurements in the Burkeville confining unit wells in northern Montgomery County (Fig.  5). Figure  9 in Montgomery County before 2020. According to the illustrates the history of Catahoula groundwater levels pumping data from LSGCD, the pumping amount from during the 2010s measured at these 13 wells. In general, the Burkeville confining unit is below 1% of the annual the Catahoula groundwater level has been declining with total-pumping in Montgomery County. GPS and exten an average rate of approximately 1.5  m/year during the someter measurements at the Lake Houston site sug- 2010s. Since the Catahoula sandstone primarily com- gest no considerable groundwater-level changes in the prises consolidated sediments in Miocene and Oligocene, Burkeville confining unit during the past 4  decades. W ang et al. Geoenviron Disasters (2021) 8:28 Page 11 of 24 Fig. 9 Groundwater-level changes in the Catahoula sandstone in northern Montgomery County recorded at 13 wells. The locations of these wells are marked in Fig. 5 no considerable compaction associated with groundwa- in the Chicot aquifer; three wells were completed at dif- ter pumping is expected. ferent depths of the Evangeline aquifer, and one deep well was terminated within the top portion of the Jasper Results aquifer. The borehole of the extensometer was screened Observations at the Lake Houston site at the bottom. The screen allows groundwater to flow In general, GPS-derived subsidence represents the total in and out. Thus, the extensometer borehole (out case) compaction of unconsolidated and semi-consolidated also works as a deep groundwater well measuring the sediments below the land surface. The compaction within groundwater hydraulic head within the top portion of the a specific aquifer is often challenging to ascertain using Burkeville confining unit. HGSD installed a GPS (LKHU) GPS data alone. Combining GPS and long-term bore- antenna on the top of the inner pole in 1993 with the hole extensometer (compaction recorder) datasets may purpose of providing a stable reference for regional land provide compaction information within specific aquifers subsidence monitoring. The inner pole was anchored on (e.g., Yu et  al. 2014; Liu et  al. 2019a, b). Unfortunately, the top of the Burkeville confining unit 591 m below the there are no extensometers in Montgomery County. As land surface (Fig.  10b). A permanent GPS (P009) was of 2020, USGS and HGSD operate 14 borehole exten- installed adjacent to Lake Houston in 1999 (see Fig.  1 someters within the greater Houston region. The clos - for the location). The linear distance between P009 and est extensometer to Montgomery County is located at LKHU is 15 km. Lake Houston, Harris County, approximately 17  km to the south boundary of Montgomery County (Fig. 1). The Evangeline compaction extensometer measurements (1980–2020) are provided Figure 11a depicts the Lake Houston extensometer and by USGS (Ramage and Shah 2019). Land surface eleva- GPS (LKHU) measurements during the past 4 decades. tion at this site is approximately 16  m above mean sea The extensometer measured the total compaction of level. sediments from the land surface to the bottom of the The extensometer borehole at Lake Houston was ter - Evangeline aquifer. The average compaction rate was minated at the top of the Burkeville confining unit, 11.8  mm/year during the 1980s, reduced to 3.8  mm/ 591  m below the land surface (Fig.  10a). Six groundwa- year during the 1990s, and further reduced to approxi- ter observation wells were also installed adjacent to the mately 1.3  mm/year during the 2000s. The GPS meas - extensometer site (Fig.  10b). Two wells were terminated urements (LKHU) on the top of the inner pole indicate Wang et al. Geoenviron Disasters (2021) 8:28 Page 12 of 24 Groundwater wells LKHU Antenna Pole Inner Pole Lake Houston Borehole Extensometer (a)(b) Out Case Fig. 10 a A sketch showing the depths of groundwater wells at the Lake Houston site; b a site photo showing extensometer, GPS, and groundwater wells at the Lake Houston site. The GPS antenna ( TXCN) is mounted on the top of the inner pole of the extensometer, which is anchored at the top of the Burkeville confining unit, 591 m below the land surface no considerable vertical movements during the entire derived from GPS and extensometer datasets agree rea- history from 1993 to 2020. That is, no groundwater- sonably well (− 1.3  mm/year vs . − 1.8  mm/year), which withdrawal-induced aquifer compaction occurred also suggests no considerable compaction below the within the Burkeville confining unit and the Jasper Evangeline aquifer. aquifer at this site. Figure 11b illustrates the groundwater levels recorded GPS-derived subsidence time series at P009 indi- at these seven groundwater-level observation wells. The cates that the ongoing land subsidence (total compac- deep Chicot well (USGS ID: 295451095083901, 165  m tion) rate in this area has been about 1.8 mm/year since below land surface) shows a consistent groundwater- the 2000s. There are tall trees around P009; therefore, level change pattern with these Evangeline groundwa- the scatters of the subsidence time series at P009 are ter levels. It is likely that the groundwater level in this remarkably larger than the scatters at other GPS sites. well was dominated by the groundwater-level change According to the empirical formula (Eq.  1) for estimat- in the Evangeline aquifer. This implies that the inter - ing the accuracy (95% CI) of GPS-derived vertical site face between the Chicot and the Evangeline aquifers at velocities, the two-decadal observations (1999–2020) this site is close to 165  m below the land surface. The would be long enough to secure submillimeter-per- units that make up the Chicot and Evangeline aquifers year accuracy for estimating an overall linear trend are similar in lithology and are difficult to differentiate (subsidence rate) (Wang 2021). The extensometer data (Baker 1979). The Chicot and Evangeline aquifers are indicates that the average subsidence rate during this hydraulically connected, which allows groundwater to period (1999–2020) is approximately 1.3  mm/year. flow between them. The shallow Chicot well (USGS ID: According to an analysis of co-located and closely- 295449095083401, 60  m below land surface) shows a spaced daily-GPS and monthly-extensometer meas- slight rise (0.2 m/year) of the Chicot groundwater level urements at Addicks in northwestern Houston (Wang from approximately − 18 m in 1980 to − 10 m in 2020. et  al. 2014), the root-mean-square (RMS) accuracy of The Chicot groundwater level has been above the pre- the monthly-extensometer measurements is a few mil- consolidation head since the 1990s. It is unlikely that limeters. The accuracy (95% CI) of the compaction rate the Chicot aquifer could considerably contribute to the derived from the 20-year monthly-extensometer data land surface subsidence since the 1990s. Thus, the total (1999–2020) is certainly below 1 mm/year. Considering aquifer compaction recorded by the extensometer dur- the uncertainty of both datasets, the subsidence rates ing the past 3 decades is solely contributed by the com- paction of the Evangeline aquifer. W ang et al. Geoenviron Disasters (2021) 8:28 Page 13 of 24 Fig. 11 Land subsidence and groundwater-level changes at the Lake Houston site. The green box indicates the virgin-compaction phase. The relative locations of wells, extensometer, and GPS are illustrated in Fig. 10. The location of GPS station P009 is marked in Fig. 1 Pre‑consolidation head ′ p = p − u , (2) The correlation between the primary aquifer compac - tion and groundwater-level changes can be explained where p represents effective stress at the grain-to-grain by the Principle of Effective Stress (Terzaghi 1925): contact points within the sediments; p represents total Wang et al. Geoenviron Disasters (2021) 8:28 Page 14 of 24 stress due to the weight of the overlying water and sedi- than the land elevation in southern Harris County, a ments; u represents pore-fluid stress, which is corre - slight hydraulic gradient would occur over the long dis- sponding to the hydraulic head within local sediments. tance from the north to the south. Combining the obser- u can be divided into two parts: a static or equilibrium vations at this site and the pre-consolidation head in head ( u ) in the pore water and a transient pore-water southern Harris County, we deduce that the Evangeline stress ( u ) in excess of the equilibrium pore-water stress. pre-consolidation head in Lake Houston area is approxi- That is, u = u + u . Within aquitards, u decays to zero mately at − 15 to − 25 m, 5 m higher than the pre-consol- w s slowly as water drains from an aquitard and stress equi- idation head in southern Harris County. Determination librium is approached. The total stress ( p ) is also called of the pre-consolidation head will be further discussed in geostatic stress, often regarded as unchanged during the following sections. The long-term static groundwa - multi-decadal to century time scales. The total stress ter hydraulic heads in the two aquifers are approaching ( p ) is balanced by the changes of pore-fluid pressure the same level since the groundwater in the Chicot and ( u ) and effective stress ( p ) exerted on clay particles. the Evangeline aquifers are hydraulically connected. The Pumping causes the reduction of pore-water stress ( u ) pre-consolidation head in the Chicot aquifer would be in response to the declining of the hydraulic head. The the same as the pre-consolidation head in the Evangeline reduced stress will be taken over by the solid grains. The aquifer. maximum effective stress that a lay of sediments had The groundwater level in the extensometer borehole sustained for a long period (century-scale) during its (USGS ID: 295449095084105, completed at 591 m below history is called pre-consolidation stress. When the effec - land surface) was relatively stable during the past 4  dec- tive stress exceeds the pre-consolidation stress, the clay ades, ranging from − 25 to − 35  m (Fig.  11b). Since the grains will undergo significant, permanent rearrange - borehole is terminated within the top of the Burkeville ment, resulting in inelastic (irreversible) compaction. The confining unit, the groundwater level represents the groundwater level corresponding to the pre-consolida- groundwater hydraulic head in the Burkeville confin - tion stress is called the pre-consolidation hydraulic head, ing unit. The thickness of the Burkeville confining unit simply the pre-consolidation head. In the Greater Hou- is approximately 100  m in this area. The GPS antenna ston region, the pre-consolidation head in each aquifer (LKHU) on the inner pole of the extensometer was stable is approximate to the groundwater level before the 1940s over the past 2 decades, indicating no considerable com- when no excessive groundwater pumping occurred. paction within the confining unit. The Evangeline wells indicate that the groundwater The groundwater level in the Jasper well (USGS ID: hydraulic head remained constant during the 1980s, 295449095084101, 790  m below land surface) shows a approximately at − 50 m (Fig. 11b). According to ground- gentle decline from 1980 to 2000 with an average decline water data in the long history illustrated in Fig.  7, rate of 0.5  m/year. A rapid groundwater-level drop of regional-scale groundwater decline began in the 1970s. 10  m occurred within 2  years from 2002 to 2003, which The Evangeline groundwater level started to rise in the did not induce any significant subsidence at the land sur - early 1990s and reached approximately − 35 m at the end face. The Jasper groundwater continued to decline from of 2008. Extensometer measurements indicate that the 2004 to 2014 with an average rate of − 2.5  m/year. The compaction of Evangeline was about 1  mm/year from decline rate slowed down since 2016 with an average 2000 to 2008. The minor subsidence rate suggests that the rate of − 0.6  m/year (2016–2020). The Japer groundwa - groundwater level was approaching the pre-consolidation ter-level altitude declined to − 10  m at the beginning of head. A slight aquifer elastic expansion (or land surface 2020. Since there is no groundwater-withdrawal-induced rebound) is expected if the groundwater level had recov- compaction within the Jasper aquifer as verified by GPS ered to the pre-consolidation head (e.g., Galloway and data (LKHU), the Jasper pre-consolidation head in this Burbey 2011; Liu et al. 2019a; Zhou et al. 2021). Since no area would be lower than the current groundwater level rebound was recorded around this period by the exten- (− 10 m). someter, it is most likely that the Evangeline groundwater level (− 35 m) as of 2008 is still below the pre-consolida- Virgin‑compaction/head‑decline ratio tion head. The aquifer compaction that occurred when the ground - According to the investigations of USGS (e.g., Kas- water level is below the pre-consolidation head is also marek and Robinson 2004; Kasmarek 2012) and UH referred to as virgin compaction in the hydrology litera- (Kearns et  al. 2015, 2019), the pre-consolidation heads ture (e.g., Helm 1975; Galloway and Burbey 2011). The of the Chicot and Evangeline aquifers are approximately increased effective stress that exceeds the maximum his - − 20 to − 30 m in southern Harris County. Since the land toric stress (pre-consolidation stress) during the virgin elevation in the Lake Houston area is about 10 m higher compaction phase is called virgin stress. In this article, W ang et al. Geoenviron Disasters (2021) 8:28 Page 15 of 24 the virgin compaction is specifically referred to as the on the other hand, it is difficult to get the groundwater compaction that occurred when the groundwater level and compaction measurements during the virgin-com- was continuously declining and below the pre-consoli- paction phase. The groundwater levels have been rising dation head, distinguishing it from the compaction that while the land surface is continuously subsiding in the occurred when the groundwater level was stable or rising majority part of northern Harris and Montgomery coun- (see Fig. 11a). ties since the mid-2010s. So, most GPS data are collected The Evangeline wells completed at different depths during the non-virgin-compaction phase. Fortunately, indicate a rapid Evangeline groundwater-level drop of the datasets at Lake Houston provide valuable informa- 5  m from mid-2008.5 to 2013 (Fig.  11b), which resulted tion to delineate the virgin-compaction/head-decline in a compaction of 2  cm within the Evangeline aqui- ratio in the Evangeline aquifer in this region. fer during the period from mid-2009 to 2014 (Fig.  11a). In summary, the long-history of groundwater, exten- Compaction occurs primarily due to the change in pore someter, and GPS datasets at the Lake Houston site have pressure in the clay beds in an aquifer. It takes time for contributed to essential conclusions: (1) groundwater the pressure change in the sand to propagate into the pumping has not induced considerable compactions in clay, for the compaction of clay to occur, and for the deep the Burkeville confining unit and the Jasper aquifer in compaction to propagate to the land surface ultimately. this area; (2) the pre-consolidation head in the Evange- The time lag between groundwater level drop and land line aquifers would be slightly higher than − 30  m, and subsidence occurring at this site is about 1 year. The 5-m the pre-consolidation head in the Jasper aquifer would groundwater-level decline in the Evangeline aquifer led be deeper than − 10 m; (3) the virgin-compaction/head- to a 2-cm virgin-compaction at this site. The ratio of vir - decline ratio in the Evangeline aquifer is approximately gin-compaction to head-decline is approximately 1:250. 1:250 in the Lake Houston area. This ratio is a direct measure of the virgin compressibil - ity of the Evangeline aquifer in this area. The compress - Observations in The Woodlands ibility is related to the geologic age, burial depth, and The Woodlands is located in southern Montgomery content (thickness) of clay layers within the aquifer. The County, 45  km north of Houston. The terrain is essen - Lake Houston site is only 17  km away from Montgom- tially flat, ranging from 40 to 60  m above sea level. The ery County. According to USGS investigations (e.g., Kas- Woodlands is one of the fastest-growing suburban areas marek and Robinson 2004), the clay layers within the top in Texas. Groundwater pumping has increased signifi - aquifers (Chicot, Evangeline, upper Jasper) are similar on cantly since the 2000s. both sides of the boundary between Harris and Mont- gomery counties. Evangeline virgin‑compaction/head‑decline ratio In practice, it is a challenge to estimate the virgin com- Figure  12a shows the locations of six GPS stations pressibility of an aquifer. On the one hand, it is often diffi - and three sets of closely-spaced Evangeline and Jasper cult to measure the compaction within a specific aquifer; groundwater wells in The Woodlands area. Figure  12b, c (a) (b) (c) P013 WHCR Fig. 12 a Map showing the locations of GPS and groundwater-level observation wells in The Woodlands area; b the permanent GPS antenna pole and solar power system at P013; c GPS antenna WHCR, which is located in The Woodlands High School. The LiDAR data for plotting the DEM map is available at NOAA (https:// coast. noaa. gov/ datav iewer) Wang et al. Geoenviron Disasters (2021) 8:28 Page 16 of 24 show site views at GPS stations P013 and WHCR. P013 is are in a none-virgin-compaction phase. The compress - a typical PAM station installed on the free field. WHCR ibility of each aquifer during the non-virgin-compaction is a typical UH GPS station installed on school buildings. phase could be differ from the compressibility during the GSEC, PWES, and WHCR are installed on single-story virgin-compaction phase. school buildings in Galatas Elementary School, Powell Elementary School, and The Woodlands High School. Jasper pre‑consolidation head Figure  13a depicts the GPS-derived land subsidence GPS-derived subsidence at P013 shows a reduction of time series at these GPS sites. GPS-derived subsidence the subsidence rate in the middle of 2004. The subsid - time series at these six sites consistently suggest that the ence rate was 11  mm/year from 2001 to 2003, which is average rate of ongoing subsidence (2016–2020) in this comparable to the rate that could be produced by the area is approximately 7–8  mm/year. P013 has a history compaction of the Evangeline aquifer alone (~ 10  mm/ of 2  decades (2000–2020) and shows the occurrence of year) with the groundwater hydraulic head decline rate of an acceleration of subsidence in the middle of 2004. The 2.4  m/year. There were no substantial groundwater-level subsidence rate changed from 11 mm/year (2001–2004.5) changes in the Evangeline aquifer around 2004. So, the to 16  mm/year (2005–2015). There has been a decelera - increased subsidence rate (from 11 to 16 mm/year) might tion of subsidence since 2016. The Woodlands area began be primarily contributed by the additional compaction of receiving surface water from Lake Conroe in 2015. Sub- the Jasper aquifer. In other words, the compaction of the sequently, land subsidence reduced from 16  mm/year Jasper aquifer likely began in 2004. The Jasper groundwa - (2005–2015) to 8 mm/year (2016–2020). ter level in 2004 would be close to the pre-consolidation Figure  13b depicts the history of groundwater-level head of the Jasper aquifer. Figure  13b indicates that the changes in The Woodland area. Measurements at three Jasper groundwater-level altitude in 2004 was approxi- Evangeline wells indicate that the Evangeline ground- mately − 25  m. The observations at the Lake Houston water-level altitude was below the pre-consolidation site already concluded that the pre-consolidation head head and declined with a steady rate of 2.4 m/year from in the Jasper aquifer must be below − 10  m. It is very 2001 to 2014. The groundwater level began to rise after likely that the pre-consolidation head in the Jasper aqui- the surface water was available for municipal use since fer is between − 15 and − 25  m, which is similar to the approximately 2015. The observations at the Lake Hou - pre-consolidation heads in the Chicot and Evangeline ston site have suggested that the Evangeline virgin-com- aquifers in this area. The land elevation at P013 is approx - paction/head-decline ratio in this area is about 1:250 imately 50  m above sea level. The Jasper pre-consolida - (Fig.  11). The groundwater-level decline of 2.4  m/year tion head in this area would be 65–75 m below the land in the Evangeline aquifer would result in a compaction surface. approximately 10  mm/year. GPS measurements at P013 In summary, the observations at The Woodlands sug - indicate that the total compaction rate was 16  mm/ gest: (1) the compaction in the Jasper aquifer began in year from 2004 to 2015. The compactions of the Chicot the mid-2000s in The Woodlands area and contributed aquifer and the Burkeville confining unit are ignorable, to approximately one-third of the land subsidence from as previously discussed. That means the compaction of the mid-2000s to mid-2010s; (2) the pre-consolidation the Jasper aquifer resulted in the remaining 6  mm/year. head of the Jasper aquifer is approximately at − 15 to The measurements at three Jasper wells closely-spaced − 25  m; (3) the virgin-compaction/head-decline ratio in with these three Evangeline wells indicate that the Jasper the Jasper aquifer is approximately 1:800 in Montgomery groundwater-level decline rate was approximately 4.8 m/ County. year from 2004 to 2014. Accordingly, the virgin-compac- tion/head-decline ratio in the Jasper aquifer in this area is Observations in the City of Conroe approximately 1:800. That is, the Jasper Aquifer is three The City of Conroe is the county seat, the economic to four times less susceptible to compaction than the and geographic center of Montgomery  County (Fig.  5). overlying Evangeline aquifer in this area. Figure  14a depicts four permanent GPS stations, three The groundwater level and GPS datasets also suggest Chicot wells, one Evangeline well, and six Jasper wells that the Jasper aquifer contributed approximately one- in the Conroe area. Figure  14b shows a site photo at the third of the total compaction (6 of 16  mm/year) from GPS antenna TXCN, mounted on the roof of the office 2005 to 2015. Unfortunately, it is difficult to distinguish building of TxDOT at Conroe. Figure 15 illustrates GPS- the contribution of the Jasper aquifer from the land sub- derived subsidence and groundwater level changes dur- sidence (total compaction) since 2016. Groundwater lev- ing the past 2  decades. TXCN (2004–2020) recorded els in both the Jasper and Evangeline aquifers have been steady subsidence from 2007 to 2015 with an average rate rising since 2016. The ongoing compactions since 2016 of − 14  mm/year. The subsidence rate has been reduced W ang et al. Geoenviron Disasters (2021) 8:28 Page 17 of 24 Fig. 13 GPS-derived subsidence and groundwater levels in The Woodland area. The locations of these wells and GPS are marked in Fig. 12 Wang et al. Geoenviron Disasters (2021) 8:28 Page 18 of 24 (b) (a) TXCN Fig. 14 a Map showing the locations of GPS stations and groundwater-level observation wells in the Conroe area; b GPS antenna TXCN, mounted on the roof of the Texas Department of Transportation office building in the City of Conroe, Montgomery County. The LiDAR data for plotting the DEM map is available at NOAA (https:// coast. noaa. gov/ datav iewer) to 6  mm/year since 2016. Observations at other three groundwater levels in all aquifers (Chicot, Evangeline, GPS stations (UH02, P070, P071) also suggest that the Jasper) were above their pre-consolidation heads (− 15 to ongoing subsidence rate is approximately 6  mm/year − 25 m). in this area (Fig.  15a). There is only one Evangeline well In summary, the compaction of the Evangeline aqui- (USGS ID: 301614095284201, terminated 216  m below fer began in the early 2000s in the Conroe area, and the land surface) in the Conroe area, which indicates a compaction of the Jasper aquifer began in the mid-2000s. groundwater level decline rate of 2.7 m/year (2004–2013) The Jasper compaction contributed approximately one- (Fig.  15b). The Jasper groundwater level declined with third of the total compaction (subsidence) from 2007 to a rate of 3.2  m/year during the same period. The 2.7  m/ 2015. The observations in the Conroe area confirmed year groundwater-level decline in the Evangeline aquifer that the estimates of pre-consolidation heads and virgin- would lead to subsidence of approximately 11  mm/year compaction/head-decline ratios in the Evangeline and based on the virgin-compress/head-decline ratio of 1:250; Jasper aquifers are reasonable. the 3.2 m/year groundwater-level drop in the Jasper aqui- fer will lead to subsidence of approximately 4  mm/year Observations in the Southeast area based on the virgin-compress/head-decline ratio of 1:800. Figure 16 depicts land subsidence and groundwater-level The total subsidence rate would be about 15  mm/year. changes in southeastern Montgomery County and adja- GPS station TXCN did record land surface subsidence of cent areas. Locations of groundwater-level observation 14 mm/year during this period (2007–2015). The analyti - wells and GPS are marked in Fig.  5. GPS station P072 cal solution (15  mm/year) and the direct measurement is in the New Caney area. P012 is next to the southeast (14  mm/year) agree with each other, which further veri- border of Montgomery County, adjacent to Kingwood, fies that the estimated virgin-compaction/head-decline the largest master-planned residential community in ratios are reasonable. northern Harris County and southern Montgomery The groundwater level in the Jasper aquifer declined County. COH6 and P065 are two GPS stations in Harris to below − 25  m in the early 2006. GPS-derived subsid- County, approximately 5  km from Montgomery County. ence time series at TXCN indicated a rapid drop of the GPS-derived subsidence at these four sites indicates that land surface at the end of 2006 (Fig.  15a). The additional the ongoing subsidence since the 2010s in southeastern compaction of the Jasper aquifer possibly caused the Montgomery County is about 5–8  mm/year (Fig.  16a). increased subsidence rate. So, − 25 m is a reasonable esti- The Evangeline groundwater level was stable and close mate of the lower bound of the pre-consolidation head to the pre-consolidation head during past 3  decades in the Jasper aquifer. According to the declining trend of (Fig. 16b). the Evangeline groundwater, the Evangeline groundwa- The Jasper well at the eastern border (USGS ID: ter level in the Conroe area was above the pre-consoli- 301911095092901), near Cleveland, indicates that the dation before 2000. In other words, land subsidence in Jasper groundwater level has been declining over its the Conroe area would be minor before 2000 since the entire history since the 1990s and is still above the W ang et al. Geoenviron Disasters (2021) 8:28 Page 19 of 24 Fig. 15 GPS-derived land subsidence and groundwater-level changes in Conroe area. The locations of these wells and GPS are marked in Fig. 14 Wang et al. Geoenviron Disasters (2021) 8:28 Page 20 of 24 Fig. 16 GPS-derived land subsidence and groundwater levels in southeastern Montgomery County. The locations of GPS stations and groundwater wells are marked in Fig. 5 W ang et al. Geoenviron Disasters (2021) 8:28 Page 21 of 24 pre-consolidation head as of 2020 (Fig.  16c). The Jasper also approximately one-third of the land subsidence well near Splendora (USGS ID: 301443095091801) indi- (6 mm/year vs. 15–20 mm/year) during the virgin com- cates that the Jasper groundwater has been approach- paction phase. Both the Evangeline and Jasper ground- ing the pre-consolidation head since the mid-2010s. The water-level altitudes are approximately 30  m below Jasper well (USGS ID: 301016095165501) close to P012 their pre-consolidation heads as of 2020. Land subsid- shows that the Jasper groundwater level declined to the ence will continue until groundwater levels in both the pre-consolidation head in 2006 and reached the lowest Evangeline and Jasper aquifers recover to their pre-con- level in 2014. The Jasper groundwater level began to rise solidation heads. in 2015 following the reduction of groundwater pumping. The average decline rate of the Jasper groundwater level was approximately 5.0 m/year (2004–2014), which would Discussion produce approximately 6 mm/year compaction according Land subsidence is probably one of the most evident to the virgin-compaction/head-decline ratio of 1:800. The environmental effects of excessive groundwater pump - analytical compaction rate of 6  mm/year within the Jas- ing. The GPS-derived positional time series presented in per aquifer is comparable with the total compaction rates this study suggest that the rate of subsidence varies con- (5–8 mm/year) recorded by GPS in this area. That is, the siderably over time and space, depending on groundwa- ongoing land subsidence in this area is dominated by the ter levels and the changes of groundwater levels in both compaction of the Jasper aquifer. This result is consistent the Evangeline and Jasper aquifers. A remarkable reduc- with the fact that the Chicot and Evangeline groundwater tion of the subsidence rate has been recorded by GPS levels were above their pre-consolidation head during the in central and southern Montgomery County since the past 2 decades (Fig. 16b). mid-2010s due to the reduction of pumping as a result of In summary, the observations in southeastern Mont- groundwater regulation. The observations presented in gomery County indicate that land subsidence in this this study reveal that land subsidence is a human-induced area is dominated by the compaction of the Jasper aqui- “natural” hazard depending on how groundwater is man- fer since the late 2000s. The observations further con - aged and regulated. firm that the estimates of regional pre-consolidation LSGCD adjusted its groundwater regulation rules in heads and the virgin-compaction/head-decline ratios are 2020. The 2020 regulatory plan no longer requires the reasonable. large volume groundwater users to follow the previous rule of reducing their groundwater production by thirty percent (30%) of their Total Qualifying Demand (LSGCD Observations in the Southwest area 2020). It is likely that the groundwater levels in Mont- Figure  17 illustrates GPS-derived subsidence and gomery County, as well as in its neighboring counties, groundwater-level changes in southwestern Mont- will further decline in the future. As of 2020, the Jasper gomery County. Locations of these GPS stations and groundwater-level altitude is approximately 20–40  m groundwater wells are marked in Fig.  5. GPS sta- below the pre-consolidation head in central and southern tions P017 and ROD1 are located in northern Harris Montgomery County; the Evangeline groundwater-level County, approximately 5  km to Montgomery County. altitude is about 40–60  m below the pre-consolidation GPS measurements at P017 indicate that the subsid- head in southern Montgomery County. Subsidence will ence rate was up to 2  cm/year during the 2000s and continue to occur as long as the groundwater hydrau- slowed down since the mid-2010s. The ongoing subsid - lic head in either the Evangeline or the Jasper aquifer ence in this area is about 7–12  mm/year (2015–2020) remains below its pre-consolidation head. (Fig. 17a). The Chicot groundwater level was stable and GPS and groundwater monitoring datasets in Mont- above the pre-consolidation during the past 3 decades. gomery County provide first-hand information for The Evangeline groundwater level declined to below the tracking land subsidence and understanding the cause- pre-consolidation head in the late 1990s and retained and-effect relationship in groundwater-level changes and stable during the 2010s (Fig.  17b). The Jasper ground - aquifer compactions. By 2020, subsidence over 5  mm/ water level declined to the pre-consolidation head in year is ongoing in central and southern Montgomery the mid-2000s and retained stable during the 2010s County, approximately half the area of the entire county. (Fig.  17c). The Jasper groundwater level declined with Continuously conducting county-wide groundwater- a rate of 5  m/year during the virgin-compaction phase level and land subsidence monitoring is essential for (2005–2010). According to the virgin-compaction/ understanding the temporospatial progress of subsid- head-decline ratio of 1:800, the 5  m/year head-decline ence and for future groundwater supply planning and would result in approximately 6  mm/year of compac- management. tion. The contribution of the Jasper compaction was Wang et al. Geoenviron Disasters (2021) 8:28 Page 22 of 24 Fig. 17 GPS-derived land subsidence and groundwater levels in southwestern Montgomery County. The locations of GPS stations and groundwater wells are marked in Fig. 5 W ang et al. Geoenviron Disasters (2021) 8:28 Page 23 of 24 Received: 17 June 2021 Accepted: 20 October 2021 Conclusions Based on the long-term groundwater level and land subsidence observations in the Montgomery County and northern Harris County, we conclude that: References Agudelo G, Wang G, Liu Y, Bao Y, Turco MJ (2020) GPS geodetic infrastructure (1) the pre-consolidation heads of the three aquifers for subsidence and fault monitoring in Houston, Texas, USA. Proc Int Assoc Hydrol 382:11–18 in the Montgomery County area are close to each Baker ET, Jr (1979) Stratigraphic and hydrogeologic framework of part of the other, approximately 15–25 m below sea level; coastal plain of Texas. Texas Department of Water Resources Report 236, (2) the compactions from the Chicot aquifer and the p 43 Braun CL, Ramage JK (2020) Status of groundwater-level altitudes and long- Burkeville confining unit during the past 3 decades term groundwater-level changes in the Chicot, Evangeline, and Jasper would be minor even if they did occur; aquifers, Houston-Galveston region, Texas, 2020. U.S. Geological Survey (3) the ongoing subsidence in Montgomery County Scientific Investigations Report 2020–5089, p 18 Campbell MD, Campbell MD, Wise HM (2018) Growth faulting and subsidence since the mid-2000s has been dominated by the in the Houston, Texas area: guide to the origins, relationships, hazards, compactions of the Evangeline and Jasper aquifers; potential impacts and methods of investigation: an update. J Geol Geosci (4) the compaction of the Jasper aquifer began in the 2:1–53 Casarez IR (2020) Aquifer extents in the coastal lowlands aquifer system mid-2000s in The Woodlands and Conroe areas and regional groundwater availability study area in Texas, Louisiana, Missis- contributed about one-third of the land subsidence sippi, Alabama, and Florida. U.S. Geological Survey data release. https:// since the mid-2000s; doi. org/ 10. 5066/ P9BH2 KG2 Chowdhury AH, Turco MJ (2006) Geology of the Gulf coast aquifer, Texas. Texas (5) the virgin-compaction/head-decline ratio is approx- Water Dev Board Rep 365:23–50 imately 1:250 in the Evangeline aquifer and 1:800 in Coplin LS, Galloway D (1999) Houston-Galveston, Texas. Land subsidence in the Jasper aquifer in central and southern Mont- the United States. US Geol Surv Circ 1182:35–48 Furnans J, Keester M, Colvin D, Bauer J, Barber J, Gin G, Danielson V, Erickson L, gomery County. Ryan R, Khorzad K, Worsley A, Snyder G (2018) Final report: identification of the vulnerability of the major and minor aquifers of Texas to subsid- ence with regard to groundwater pumping. Texas Water Development Acknowledgements Board, Contract report No. 1648302062, p 434 The authors acknowledge LSGCD, HGSD, USGS, TxDOT, SmartNet, and Gabrysch RK (1967) Development of ground water in the Houston district, UNAVCO for archiving and sharing groundwater and GPS data with the public. Texas, 1961–65. Texas Water Dev Board Rep 63:35 The authors acknowledge the comments and suggestions from Mr. Michael R. Galloway DL, Burbey TJ (2011) Review: regional land subsidence accompany- Keester (LRE water) and two anonymous reviewers. Figs. 1, 4, 5, 8, 12a, and 14a ing groundwater extraction. Hydrogeol J 19:1459–1486 are generated using the Generic Mapping Tools (GMT ), developed by Wessel Greuter A, Petersen P (2021) Determination of groundwater withdrawal and et al. (2013). subsidence in Harris and Galveston counties—2020. Harris-Galveston Subsidence District Report. https:// hgsub siden ce. org/ wp- conte nt/ uploa Authors’ contributions ds/ 2021/ 05/ 2020- HGSD- AGR_ Full- Report- 1. pdf K.W. and G.W. processed data and prepared the draft. B.C., H.L., and Y.B. Helm DC (1975) One-dimensional simulation of aquifer system compaction analyzed data, reviewed, and edited the manuscript. All authors read and near Pixley, Calif.: 1. constant parameters. Water Resour Res 11(3):465–478 approved the final manuscript. Kasmarek MC (2012) Hydrogeology and simulation of groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer Funding system, Texas, 1891–2009 (ver. 1.1, December 2013). U.S. Geological Hanlin Lius’s contribution to this work was supported by the National Key R&D Survey Scientific Investigations Report 2012–5154, p 55 Program of China (No. 2019YFB2102700); Yan Bao’s contribution to this work Kasmarek MC, Robinson JL (2004) Hydrogeology and simulation of ground- was supported by National Science Foundation of China (No. 51829801). water flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system, Texas. U.S. Geological Survey Scientific Investiga- Availability of data and materials tions Report 2004–5102, p 111 GPS raw data used for this study are available at HGSD (https:// hgsub siden Kasmarek MC, Ramage JK, Johnson MR (2016) Water-level altitudes 2016 and ce. org), UNAVCO (https:// www. unavco. org), and NGS (https:// www. ngs. noaa. water-level changes in the Chicot, Evangeline, and Jasper aquifers and gov/ CORS). The groundwater measurements are available at USGS (https:// compaction 1973–2015 in the Chicot and Evangeline aquifers, Houston- water data. usgs. gov/ nwis). All processed data, models, or code that sup- Galveston region, Texas. U.S. Geological Survey Scientific Investigations port the findings of this study are available from the corresponding author Map 3365, pamphlet, 16 sheets, scale 1:100,000 (gwang@uh.edu) upon request. Kearns TJ, Wang G, Bao Y, Jiang J, Lee D (2015) Current land subsidence and groundwater level changes in the Houston metropolitan area Declaration (2005–2012). J Surv Eng 141(4):05015002 Kearns TJ, Wang G, Turco MJ, Welch J, Tsibanos V, Liu H (2019) Houston16: a Competing interests stable geodetic reference frame for subsidence and faulting study in the The authors declare no conflict of interest. Houston metropolitan area, Texas. US Geod Geodyn 10(5):382–393 Kelley V, Deeds N, Young SC, Pinkard J, Sheng Z, Seifert J, Marr S (2018) Subsid- Author details ence risk assessment and regulatory considerations for the brackish Department of Earth and Atmospheric Sciences, University of Houston, Jasper aquifer—Harris-Galveston and Fort Bend Subsidence Districts. Houston 77204, USA. Institute of Urban Smart Transportation and Safety Report prepared for Harris-Galveston Subsidence District and Fort Bend Maintenance, Shenzhen University, Shenzhen 518060, China. K ey Laborator y Subsidence District, p 69 of Urban Security and Disaster Engineering of Ministry of Education, Beijing Khan SD, Stewart RR, Otoum M, Chang L (2013) A geophysical investigation University of Technology, Beijing 100029, China. of the active Hockley fault system near Houston, Texas. Geophysics 78:B177–B185 Wang et al. Geoenviron Disasters (2021) 8:28 Page 24 of 24 Liu Y, Li J, Fang Z (2019a) Groundwater level change management on control Wang G, Soler T (2014) Measuring land subsidence using GPS: ellipsoid height of land subsidence supported by borehole extensometer compaction vs. orthometric height. J Surv Eng 141:05014004 measurements in the Houston-Galveston region. Texas Geosci 9(5):223 Wang G, Yu J, Ortega J, Saenz G, Burrough T, Neill R (2013) A stable reference Liu Y, Sun X, Wang G, Turco MJ, Agudelo G, Bao Y, Zhao R, Shen S (2019b) frame for the study of ground deformation in the Houston metropolitan Current activity of the Long Point fault in Houston, Texas constrained by area, Texas. J Geod Sci 3:188–202 continuous GPS measurements (2013–2018). Remote Sens 11(10):1213 Wang G, Yu J, Kearns TJ, Ortega J (2014) Assessing the accuracy of long-term LSGCD (2013) Lone Star Groundwater Conservation District Management subsidence derived from borehole extensometer data using GPS obser- Plan—re-adopted November 12, 2013. https:// www. lones targcd. org/ vations: case study in Houston, Texas. J Surv Eng 140(3):05014001 distr ict- rules-1 Wang G, Welch J, Kearns T, Yang L, Serna J Jr (2015) Introduction to GPS LSGCD (2020) 2020 Lone Star Groundwater Conservation District Manage- geodetic infrastructure for land subsidence monitoring in Houston, Texas, ment Plan, as approved on May 15, 2020. https:// www. lones targcd. org/ USA. Proc Int Assoc Hydrol Sci 372:297–303 distr ict- rules-1 Wang G, Turco M, Soler T, Kearns TJ, Welch J (2017) Comparisons of OPUS and Miller MM, Shirzaei M (2019) Land subsidence in Houston correlated with PPP solutions for subsidence monitoring in the greater Houston area. J flooding from Hurricane Harvey. Remote Sens Environ 225:368–378 Surv Eng 143(4):05017005 Petersen C, Turco MJ, Vinson A, Turco JA, Petrov A, Evans M (2020) Ground- Wang G, Zhou X, Wang K, Ke X, Zhang Y, Zhao R, Bao Y (2020) GOM20: a stable water regulation and the development of alternative source waters to geodetic reference frame for subsidence, faulting, and sea-level rise stud- prevent Subsidence, Houston region, Texas, USA. Proc IAHS 382:797–801 ies along the Coast of the Gulf of Mexico. Remote Sens 12(3):350 Popkin BP (1971) Groundwater resources of Montgomery County, Texas. Texas Welch J (2018) Current ground motions in Montgomery, West Liberty, and Water Dev Board Rep 136:143 Northern Harris counties derived from continuous GPS motions. Mather Qu F, Lu Z, Zhang Q, Bawden GW, Kim J, Zhao C, Qu W (2015) Mapping ground Thesis, Department of Earth and Atmospheric Sciences, University of deformation over Houston-Galveston, Texas using multi-temporal InSAR. Houston Remote Sens Environ 169:290–306 Wessel P, Smith WHF, Scharroo R, Luis J, Wobbe F (2013) Generic map- Qu F, Lu Z, Kim JW, Zheng W (2019) Identify and monitor growth faulting ping tools: improved version released. EOS Trans Am Geophys Union using InSAR over northern greater Houston, Texas, USA. Remote Sens 94(45):409–410 11(12):1498 Young SC, Ewing T, Hamlin S, Baker E, Lupton D (2012) Final report—updating Ramage JK (2020) Depth to groundwater measured from wells completed in the hydrogeologic framework for the northern portion of the gulf coast the Chicot, Evangeline, and Jasper aquifers, Houston-Galveston region, aquifer. Contract report for the Texas Water Development Board, p 285 Texas, 2020. U.S. Geological Survey data release Young SC, Jigmond M, Deeds N, Blainey J, Ewing TE, Banerj D, Piemonti D, Ramage JK, Shah SD (2019) Cumulative compaction of subsurface sediments Jones T, Griffith C, Lupton D, Martinez G, Hudson C, Hamlin S, Sutherland in the Chicot and Evangeline aquifers in the Houston-Galveston region, J (2016) Final report: identification of potential brackish groundwater Texas (ver. 2.0, June 2020). U.S. Geological Survey data release production areas—Gulf Coast Aquifer System. Contract report to the Shah SD, Ramage JK, Braun CL (2018) Status of groundwater-level altitudes Texas Water Development Board, p 636 and long-term groundwater-level changes in the Chicot, Evangeline, and Yu J, Wang G, Kearns TJ, Yang L (2014) Is there deep-seated subsidence in the Jasper aquifers, Houston-Galveston region, Texas, 2018. U.S. Geological Houston-Galveston area. J Geophys 942834:1–11 Survey Scientific Investigations Report 2018–5101, p 18 Zhou F (2020) The correlation between current land subsidence and ground- Terzaghi K (1925) Principles of soil mechanics: I-Phenomena of cohesion of water levels in Montgomery County, Texas. Mather Thesis, Department of clays. Eng News-Rec 95(19):742–746 Earth and Atmospheric Sciences, University of Houston Thornhill MR, Keester MR (2020) Subsidence investigations—phase 1: assess- Zhou X, Wang G, Wang K, Liu H, Lyu H, Turco MJ (2021) Rates of natural subsid- ment of past and current investigations, prepared for Lone Star Ground- ence and submergence along the Texas coast derived from GPS and tide water Conservation District. https:// www. lones targcd. org/ subsi dence gauge measurements (1904–2020). J Surv Eng 147(4):04021020 Turco MJ, Petrov A (2015) Eec ff ts of groundwater regulation on aquifer-system compaction and subsidence in the Houston-Galveston Region, Texas, Publisher’s Note USA. Proc Int Assoc Hydrol Sci 372:511–514 Springer Nature remains neutral with regard to jurisdictional claims in pub- Wang G (2021) The 95% confidence interval for the GNSS-derived site veloci- lished maps and institutional affiliations. ties. J Surv Eng. https:// doi. org/ 10. 1061/ (ASCE) SU. 1943- 5428. 00003 90 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Land subsidence and aquifer compaction in Montgomery County, Texas, U.S.: 2000–2020

Loading next page...
 
/lp/springer-journals/land-subsidence-and-aquifer-compaction-in-montgomery-county-texas-u-s-5Y0iUsbQ4a

References (54)

Publisher
Springer Journals
Copyright
Copyright © The Author(s) 2021
eISSN
2197-8670
DOI
10.1186/s40677-021-00199-7
Publisher site
See Article on Publisher Site

Abstract

Groundwater-withdrawal-induced land subsidence has been a big concern in Montgomery County, Texas, U.S. since the 2000s. As of 2020, approximately half of the entire county is experiencing subsidence over 5 mm/year. This study aims to investigate ongoing land subsidence in Montgomery County using groundwater-level, extensometer, and GPS datasets. According to this study, land subsidence in Montgomery County since the mid-2000s is primar- ily contributed by sediment compaction in the Evangeline and Jasper aquifers; the compaction of Jasper aquifer contributes approximately one-third of the land subsidence since the mid-2000s; the pre-consolidation heads of the Chicot, Evangeline, and Jasper aquifers in Montgomery County are close to each other, approximately 15–25 m below mean sea level; the virgin-compaction/head-decline ratio is approximately 1:250 in the Evangeline aquifer and 1:800 in the Jasper aquifer in central and southern Montgomery County. As of 2020, the Jasper groundwater-level altitude is approximately 20–40 m below the pre-consolidation head in the central and southern Montgomery County; the Evangeline groundwater-level altitude is about 40–60 m below the pre-consolidation head. Land subsidence will con- tinue to occur as long as the groundwater-level altitude in either the Evangeline or the Jasper aquifer remains below the pre-consolidation head. Keywords: Subsidence, Pumping, GPS, Pre-consolidation head, Virgin-compaction/head-decline ratio Introduction 2015; Petersen et al. 2020). The Woodlands in Montgom - Study area ery County has become one of the most affected areas by Montgomery County is a part of the Houston–The subsidence in the Greater Houston region since the 2010s Woodlands–Sugar Land, Texas Metropolitan Statistical (Fig. 1). Area (MSA), which is often designated as Greater Hou- Montgomery County comprises approximately ston, encompassing nine counties along the Gulf Coast 2700  km of flat to gently rolling terrain, with eleva - in Southeast Texas with a population of over seven mil- tions ranging from about 40–120  m above sea level. lion people at the 2020 census estimates (Fig.  1). Land Groundwater-withdrawal-induced land subsidence subsidence has affected the Greater Houston region for was reported in southern Montgomery County in the nearly a century. As the population has grown outward early 1960s (Gabrysch 1967). Land surface deformation from Houston to the north and the northwest since the monitoring using Global Positioning System (GPS) in 1990s, groundwater pumping, in turn, land subsidence, Montgomery County began in the early 2000s. Rapid follows the same pattern of urban expansion (e.g., Cop- subsidence up to 20  mm/year was recorded by GPS in lin and Galloway 1999; Qu et al. 2015; Turco and Petrov northern Harris County and southern Montgomery County during the 2000s (e.g., Welch 2018; Zhou 2020). The ongoing land subsidence since the mid-2010s is approximately 5–7  mm/year in central Montgom- *Correspondence: gwang@uh.edu Department of Earth and Atmospheric Sciences, University of Houston, ery County and 8–10  mm/year in southern Mont- Houston 77204, USA gomery County. Over half of Montgomery County is Full list of author information is available at the end of the article © The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Wang et al. Geoenviron Disasters (2021) 8:28 Page 2 of 24 Fig. 1 Map showing the contours of average subsidence rates (2016–2020) derived from over 210 permanent GPS observations (> 3 years) within the Greater Houston region. The gray squares represent GPS sites used for creating the contour map. The subsidence rates are aligned to the Stable Houston Reference Frame (Houston20). The northwest corner of this map displays outcrops of the Gulf Coast Aquifer (Casarez 2020). The color patterns represent the areas regulated by the Harris-Galveston Subsidence District (HGSD: Areas 1, 2, 3), the Fort Bend Subsidence District (FBSD: Areas A and B), the Brazoria County Groundwater Conservation District (BCGCD), and the Lone Star Groundwater Conservation District (LSGCD) experiencing land subsidence over 5  mm/year as of Local aquifers 2020 (Fig. 1). In Montgomery County, the principal source of usable Ground deformation associated with subsidence and groundwater is the Gulf Coast Aquifer, which comprises faulting has caused frequent damages to residential five subdivisions in and around Montgomery County: buildings and public infrastructure in northern Harris from shallowest to deepest, the Chicot aquifer, the Evan- County and southern Montgomery County (e.g., Khan geline aquifer, the Burkeville confining unit, the Jas - et al. 2013; Campbell et al. 2018; Qu et al. 2019). Long- per aquifer, and the Catahoula Sandstone (Baker 1979; term subsidence also increases the flooding risk (e.g., Chowdhury and Turco 2006). These subdivisions crop Miller and Shirzaei 2019), which has a particular con- out in northwestern Montgomery County, as depicted in cern in low-lying residential areas in southern Mont- Fig.  1, where the aquifers receive recharge from precipi- gomery County. tation and surface water (Kasmarek and Robinson 2004). W ang et al. Geoenviron Disasters (2021) 8:28 Page 3 of 24 The Chicot aquifer is the youngest of the Gulf Coast Figure  3 lists the history of groundwater and surface Aquifer subdivisions, followed by the Evangeline Aquifer, water use in Montgomery County from 1984 to 2018. the Burkeville confining unit, and the Jasper aquifer. The The data is from Texas Water Development Board Catahoula sandstone is the oldest of the Gulf Coast Aqui- (TWDB) Historical Water Use Estimates Database fer System. The successively older units crop out pro - ( h t t p :/ / w w w . t w d b . t e x a s . g o v / w a t e r p l a n n i n g / w a t e r u s e s u gressively further inland at higher elevations (Figs.  1, 2). rvey/ estim ates/ index. asp). Groundwater pumping These aquifers comprise laterally discontinuous gravel, gradually increased with the county’s growth in popula- sand, silt, and clay (Baker 1979). The thickness of the tion since the 1980s and reached the maximum in 2011 Chicot aquifer in Montgomery County varies from less (~ 125 × 10  m ). Total groundwater use increased by a than 100  m in the north to approximately 200  m in the factor of ten from approximately 13 × 10 m in 1984 to south; the thickness of the Evangeline aquifer is approxi- 130 × 10  m in 2011, with the vast majority (over 90%) mately 200  m; the thickness of the Burkeville confining of groundwater use going to the municipal sector. The system is about 100 m throughout the county; the thick- extraordinary groundwater pumping from 2011 to 2013 ness of the Jasper aquifer is around 300–500  m (Popkin was resulted by the severe drought occurred during this 1971; Young et al. 2012) (Fig. 2). period in the southern U.S. The Texas State Legislature established the Lone Star Groundwater use and management Groundwater Conservation District (LSGCD) in 2001 The Chicot, Evangeline, and the upper portion of Jasper to regulate groundwater use and control subsidence in aquifers generally contain freshwater throughout the Montgomery County. According to LSGCD’s pumping county. The lower part of the Jasper and Catahoula Sand - data associated with permits, the pumping amount from stone contain slightly saline water (brackish water) in the the Chicot aquifer was approximately 2–3% of the annual northern and central parts of the county (Popkin 1971). total-pumping during the past 2  decades; the pumping Fig. 2 Generalized hydrogeologic section of the Gulf Coast Aquifers crossing Montgomery County from the south to the north. The extension of the cross-profile is illustrated in Fig. 1 (white line). The depth and thickness information of the aquifers is combined from Popkin (1971), Baker (1979), and Young et al. (2012) Wang et al. Geoenviron Disasters (2021) 8:28 Page 4 of 24 Fig. 3 Groundwater and surface water use in Montgomery County from 1984 to 2018. The water use information is combined from the Texas Water Development Board ( TWDB)’s Water Use Database (http:// www. twdb. texas. gov/ water plann ing/ water usesu rvey/ estim ates/ index. asp) amount from the Evangeline aquifer was approximately level declined throughout the county before 2015, with 50–55% of the annual total-pumping, and the pump- the most rapid decline in southern Montgomery County. ing amount from the Jasper aquifer was approximately The decline rate was about 3 m/year in the area between 40–45% of the annual total-pumping (Thornhill and The Woodlands and Conroe. The 2015–2019 Jasper Keester 2020). groundwater-level-change contours reveal that ground- LSGCD has been continuously improving its Manage- water level was rising throughout the entire county since ment Plan since it was created in 2001. The original man - 2015. The rising rate in northern Conroe and eastern The agement plan was adopted on October 14, 2003, then Woodlands was about 2 m/year. later amended and re-adopted in 2008, in 2013, and most In August 2015, the City of Conroe and seven other recently in 2020. The 2013 management plan mandated utility providers filed a lawsuit against the LSGCD over large-volume groundwater users, such as the City of Con- the district’s regulations of groundwater usage. On roe and large water utilities, to reduce their groundwater May 17, 2019, the 284th District Court in Montgom- production by thirty percent (30%) of their Total Qualify- ery County signed a Final Judgment declaring that the ing Demand (approximately their total water use amount large-volume groundwater user rules under the LSGCD’s in 2009) by January 1, 2016 (LSGCD 2013). As part of a Regulatory Plan were adopted without legal authority groundwater usage reduction plan, the San Jacinto River and consequently are unenforceable. LSGCD adjusted Authority built a surface water treatment facility in Con- its groundwater regulation rules accordingly in 2020. The roe (https:// www. sjra. net/ grp/ treat ment- plant). It began LSGCD’s 2020 Regulatory Plan no longer requires the to transfer treated surface water from Lake Conroe to large-volume groundwater users to follow the previous the central and southern county areas in 2015. Before requirement of reducing their groundwater pumping by 2015, groundwater use was about 95% of the total water thirty percent of their Total Qualifying Demand (LSGCD in Montgomery County. As of 2018, the groundwater use 2020). has reduced to approximately 85% of the total water use (Fig. 3). Motivation The reduction in groundwater pumping since the mid- The Harris-Galveston Subsidence District (HGSD), 2010s has resulted in county-wide groundwater-level United State Geological Survey (USGS), LSGCD, and recovery in both the Evangeline and Jasper aquifers. several other local agencies have been conducting Figure  4 illustrates the groundwater-level contour lines groundwater-level and subsidence monitoring for over showing Jasper groundwater changes during 5  years 4 decades in northern Harris County and southern Mont- before and after 2015. The 2010–2014 Jasper groundwa - gomery County. Groundwater pumping in northern Har- ter-level-change contours reveal that the groundwater ris County is primarily from the Chicot and Evangeline W ang et al. Geoenviron Disasters (2021) 8:28 Page 5 of 24 Fig. 4 Jasper groundwater-level changes in Montgomery County. a The change of groundwater altitude during the 5-year period from the beginning of 2010 to the end of 2014; b the change of groundwater altitude in meters during the 5-year period from the beginning of 2015 to the end of 2019. The color bar indicates the magnitude of groundwater altitude changes in meters aquifers (Greuter and Petersen 2021). The correlation the research and groundwater management communi- between subsidence and groundwater level changes and ties: (1) has aquifer compaction extended to Jasper aqui- the compressibility of the Chicot and Evangeline aquifers fer in Montgomery County? (2) If yes, how much is the in Harris County have been deliberately investigated by contribution of the Jasper aquifer to the present land USGS (e.g., Kasmarek et al. 2016; Shah et al. 2018; Braun subsidence? (3) What is the compressibility of the Jasper and Ramage 2020). One important conclusion is that the aquifer? This investigation aims to address these ques - groundwater-withdrawal-induced sediment compaction tions using publicly-available groundwater-level, exten- has not extended to the Jasper aquifer, at least in central someter, and GPS datasets. and southern Harris County. In general, the compaction is limited within the Chicot aquifer and the top portion Data and methodology of the Evangeline aquifer, approximately within 600 m to GPS data the ground surface (Yu et al. 2014). However, groundwa- The Greater Houston region is one of the earliest ter pumping in Montgomery County is primarily from urban areas to employ GPS technology for land sub- the Evangeline and Jasper aquifers. The percentage of sidence and fault monitoring. As of 2021, HGSD and Jasper groundwater pumping among total groundwa- the University of Houston (UH) have integrated over ter pumping has been gradually increasing since the 240 permanent GPS stations into their routine GPS 2010s. The upper portion of the Jasper aquifer is desig - data processing for land subsidence monitoring in the nated as the primary target for fresh water in northern Greater Houston region, approximately 2.2 × 10  km Harris County and southern Montgomery County, and (Fig. 1). There are 14 permanent GPS stations with over the lower portion of the Jasper aquifer is designated as 5-year observational history in Montgomery County as potential sources of brackish groundwater (e.g., Young of 2020 (Fig. 5). HGSD installed a new permanent GPS et  al. 2016; Kelley et al. 2018). The confined zones of the station, YORS, in the south of The Woodlands in 2020, Jasper and Evangeline aquifers retain the highest risk for in cooperation with The Woodlands Water Agency and future subsidence from pumping (Furnans et  al. 2018). the San Jacinto River Authority. P013, P012, P068, P070, There is a general lack of understanding regarding the P071, and P073 are campaign-style permanent GPS sta- compressibility and potential compaction for the Jasper tions, also known as Port-A-Measure (PAM) stations, Aquifer. Following questions have been raised in both operated by HGSD in cooperation with LSGCD. These Wang et al. Geoenviron Disasters (2021) 8:28 Page 6 of 24 Fig. 5 Map showing the locations of GPS and groundwater-level observation wells in Montgomery County and adjacent areas. A letter is added to the end of USGS well ID. “C” represents a Chicot well. “E” represents an Evangeline well. “J” represents a Jasper well PAM stations were designed for periodically repeated Woodlands, the City of Conroe, the Northeast, and the long-term monitoring. On average, PAM data was col- Southwest (Fig. 5). lected for 1 week every month before 2005 and 1 week The raw data of PAM stations are archived at HGSD. per 2  months after 2005. TXCN is a Continuously The raw data of UH GPS are archived at UH and Operating Reference Station (CORS) operated by the UNAVCO. CORS raw data are archived at National Texas Department of Transportation (TxDOT, https:// Geodetic Survey (NGS) at the National Oceanic and w w w. t x dot . gov/ inside- t x dot/ div i s ion/ inf or ma tion- Atmospheric Administration (NOAA). GPS-derived sub- techn ology/ gps. html). UH02 is a CORS jointly operated sidence time series are open to the public through HGSD. by UH and SmartNet (https:// www. smart netna. com). The subsidence time series are obtained by differenc - UHF1, UHJF, PWES, GSEC, and WHCR are continu- ing the GPS-derived ellipsoidal heights with respect to ous GPS stations operated by UH. UHF1 and UHJF are the Stable Houston Reference Frame 2020, abbreviated closely-spaced. Only the observations at UHF1 are used as Houston20. Houston20 is realized by long-term GPS in this study. The detailed information of these GPS observations at 25 Continuously Operating Reference stations is listed in Table  1. The UH GPS network con - Stations (CORS) located outside of the greater Houston sists of over 70 permanent GPS stations in the Houston region, where no considerable groundwater-withdrawal- metropolitan region (Wang et  al. 2015). Four GPS sta- induced subsidence has occurred since the 1990s tions (P017, ROD1, COH6, P065) located in northern (Agudelo et al. 2020). Harris County, adjacent to Montgomery County, are The stability of Houston20 is at a level of 0.3 mm/year also investigated in this study. P017 and P065 are PAM in each horizontal direction (NS: North–South; EW: stations. COH6 is a CORS jointly operated by the City East–West) and 0.8  mm/year in the vertical direction. A of Houston and HGSD. ROD1 is a CORS operated by detailed GPS data process strategy is addressed in Wang RODS Surveying Inc. (http:// www. rods. cc). Based on et al. (2013) and Kearns et al. (2019). The accuracy (root the distribution of GPS stations, we have investigated mean square error) of daily vertical-positions derived the land subsidence in the following four areas: The from GPS observations is 6–8  mm (Wang et  al. 2017). W ang et al. Geoenviron Disasters (2021) 8:28 Page 7 of 24 Table 1 Permanent GPS stations in Montgomery County, Texas GPS Location Observational history Vertical displacement (negative indicates Raw data archiving subsidence) Latitude Longitude Start End Years Days Total (cm) 5-year rate Operator (cm/year) P012 − 95.263 30.060 2000.9 2020.4 19.5 1331 − 12.2 − 0.6 HGSD HGSD P013 − 95.490 30.195 2000.9 2021.2 20.3 1259 − 25.2 − 1.4 HGSD HGSD P068 − 95.587 30.185 2011.8 2021.2 9.4 545 − 8.9 − 1.0 HGSD HGSD P069 − 95.459 30.199 2011.7 2021.2 9.4 556 − 10.6 − 1.1 HGSD HGSD P070 − 95.424 30.291 2011.8 2021.2 9.5 493 − 4.9 − 0.5 HGSD HGSD P071 − 95.579 30.353 2011.8 2021.2 9.5 553 − 3.8 − 0.4 HGSD HGSD P072 − 95.242 30.147 2012.0 2021.2 9.2 398 − 7.5 − 0.7 HGSD HGSD YORS − 95.469 30.110 2020.8 2021.2 0.3 126 HGSD HGSD TXCN − 95.441 30.349 2005.6 2021.3 15.7 5707 − 17.2 − 1.2 TxDOT NGS UH02 − 95.457 30.315 2015.0 2021.2 6.2 2114 − 3.6 − 0.6 UH&SmartNet UH&UNAVCO UHF1/UHJF − 95.483 30.236 2014.4 2020.7 6.3 2258 − 5.9 − 0.6 UH UH&UNAVCO WHCR − 95.505 30.194 2014.8 2021.3 6.5 2363 − 3.7 − 0.6 UH UH&UNAVCO PWES − 95.511 30.199 2015.2 2021.3 6.0 2205 − 6.1 − 0.9 UH UH&UNAVCO GSEC − 95.528 30.197 2015.8 2021.3 5.5 2008 − 2.8 − 0.7 UH UH&UNAVCO Total subsidence represents the total vertical displacement over the entire history of each GPS station The 5-year subsidence rate represents the linear trend of the subsidence time series from 2016 to 2020 YORS is a new station installed in 2020. http:// www. twdb. texas. gov/ water plann ing/ water usesu rvey/ estim ates/ index. asp For subsidence studies, users often pay more attention to secular effects (e.g., Wang et  al. 2020; Zhou et  al. the accuracy or confidence of the estimated subsidence 2021). So, GPS-derived subsidence with respect to rates (linear trends) rather than the accuracy of individ- Houston20 is principally caused by local-scale anthro- ual positions. In general, longer GPS observations would pogenic processes, primarily the aquifer compaction result in higher accuracy for estimating subsidence rates. associated with groundwater withdrawals. According Wang (2021) provides an empirical formula for estimat- to the report of Texas Drilling (http:// www. texas- drill ing the 95% confidence interval (95% CI, also called accu -ing. com/ montg omery- county), the oil and gas pro- racy) of GPS-derived vertical site velocities: duction in Montgomery County has reduced signifi- cantly since the 2000s. So far, the exact magnitude of the contribution of hydrocarbon production is still b = 5.2 × , (1) 95%CI 1.25 uncertain and remains an important issue for future investigations. where T is the year range of the time series in decimal GPS-derived heights are the distances above a years and b is the 95% confidence interval of the 95%CI smooth ellipsoid surface, which are called ellipsoidal linear trend (b) in millimeters per year. According to the heights. Conventional subsidence obtained from lev- empirical formula, 4-year continuous GPS observations eling survey is a physical quantity that refers to the would result in a subsidence-rate estimate with an accu- surface of the geoid, called orthometric heights in racy (95%CI) of 1  mm/year; 7-year continuous observa- surveying engineering. Ellipsoidal heights and ortho- tions would result in a subsidence-rate estimate with an metric heights are essentially different. The former is a accuracy (95% CI) of 0.5 mm/year. geometric quantity, while the latter is a physical-based The realization of regional reference frames has quantity. According to Wang and Soler (2014), ellip- excluded or minimized the regional “common” ground soid heights and orthometric heights would result in movements, including the secular plate movement of the same practical subsidence measurements during the North American Plate with respect to the Inter- the same time span. Accordingly, the subsidence values national GNSS Service (IGS) reference frames, glacial provided in this study can be regarded as having the isostatic adjustment (GIA), natural consolidation of same physical meaning as the conventional subsidence young sediments, surface mass loading associated with measurements obtained from leveling surveys. atmosphere and ocean, and other regional-scale minor Wang et al. Geoenviron Disasters (2021) 8:28 Page 8 of 24 Groundwater data American Vertical Datum of 1988 (NAVD88). Since the Groundwater levels in Montgomery County, Texas, have altitude of the mean sea level is approximately equivalent been periodically measured since the 1940s. Records of to zero with respect to NAVD88, the NAVD88 altitude is these measurements, known as groundwater data or well also referred to as mean sea level or simply sea level in data, are routinely published by the TWDB and USGS. practice. In this article, the groundwater-level altitudes The groundwater-level observation data used for this below mean sea level and above mean sea level are here- study are downloaded from the USGS National Water after referred to as negative and positive, respectively. For Information System (NWIS) (https:// water data. usgs. gov/ example, the groundwater-level altitude at 40  m below nwis) (Ramage 2020). Groundwater-level data collection sea level is abbreviated as − 40 m; the groundwater-level methods, data quality, and the status of groundwater altitude at 40 m above sea level is abbreviated as 40 m. levels are addressed in the most recent USGS Scientific The earliest Chicot groundwater-level measurements Investigations Report 2020-5089 (Braun and Ramage are available back to the 1980s. In general, the Chicot 2020). As of 2020, the USGS groundwater datasets com- groundwater-level altitude at each well was stable dur- prise 11 Chicot wells, 81 Evangeline wells, 99 Jasper wells, ing the past 3–4 decades and above the pre-consolidation and 13 Catahoula wells in Montgomery County (Fig. 5). head of the Chicot aquifer (Fig.  6). Determination of the Chicot pre-consolidation will be explained in the fol- The Chicot groundwater level lowing sections. There is a general trend that the Chicot Figure 6 depicts the groundwater levels recorded by these groundwater level declines from the north to the south. 11 Chicot wells in Montgomery County during the past The stability of the Chicot groundwater levels can be 3  decades. In this article, the groundwater-level alti- explained by the fact that groundwater pumping in the tudes are aligned to the height with respect to the North Chicot aquifer is minor in Montgomery County, at least Fig. 6 Groundwater levels in 11 wells completed in the Chicot aquifer in Montgomery County. In the legend, “30194809529004 (− 24 m, 73 m)” indicates USGS well number, well depth below land surface (BLS), and the elevation of land surface reference to mean sea level (MSL). The locations of these wells are marked in Fig. 5 W ang et al. Geoenviron Disasters (2021) 8:28 Page 9 of 24 during the past 2  decades. As mentioned earlier, annual plotted in Fig. 5. The Jasper groundwater level in Conroe pumping volumes from the Chicot aquifer are approxi- (USGS ID: 301828095272404, completed 373  m below mately 2–3% of the annual total pumping in Montgom- land surface) was about 60 m in the 1960s and started to ery County since the 2000s. The highest pumping rates decline since the 1970s and reached the lowest altitude from the Chicot aquifer are in The Woodlands area. It is (− 50 m) in the early 2010s, then began to rise in the mid- unlikely that the compaction of the Chicot aquifer could 2010s as a result of the groundwater regulations enforced remarkably contribute to the ongoing land subsidence by LSGCD. The Evangeline groundwater level in the (total compaction). upper Woodlands area (USGS ID: 301516095264301, terminated 214 m below land surface) followed a similar Evangeline and Jasper groundwater levels pattern with the Jasper groundwater level. As of 2020, the Groundwater-level monitoring in Montgomery County lowest groundwater-level altitudes in the Chicot, Evange- began as early as the 1940s in the Jasper aquifer and the line, and Jasper aquifers are − 10 m, − 80 m, and − 60 m, 1960s in the Evangeline aquifer. Figure  7 illustrates the respectively, in southern Montgomery County (Fig. 7). long-history groundwater-level changes in the Chicot Figure 8 depicts the contours of groundwater-level alti- aquifer (1989–2020), the Evangeline aquifer (1964–2020), tudes as of the beginning of 2020 in the Evangeline and and the Jasper aquifer (1956–2020). Groundwater-level Jasper aquifers in Montgomery County. The base contour changes at three wells with the lowest altitudes as of line (− 15  m) represents the pre-consolidation head of 2020 in the Chicot, Evangeline, and Jasper aquifer are each aquifer. The Jasper pre-consolidation-head is coinci - also illustrated in Fig.  7. The locations of these wells are dent with the 5-mm/year subsidence contour. The Jasper Fig. 7 The multi-decadal history of the Chicot, Evangeline, and Jasper groundwater levels in Montgomery County. Open symbols: groundwater-level changes at three long-history wells completed in the Chicot (1989–2020), Evangeline (1964–2020), and Jasper aquifers (1956–2020). Filled symbols: groundwater-level changes at three wells remaining the lowest altitude as of 2020 in the Chicot, Evangeline, and Jasper aquifers. Evangeline and Jasper groundwater levels began to rise in 2015 as a result of the reduction of pumping Wang et al. Geoenviron Disasters (2021) 8:28 Page 10 of 24 Fig. 8 Evangeline (blue) and Jasper (red) groundwater-level contours as of the beginning of 2020 in Montgomery County. Groundwater-level altitudes are referenced to the mean sea level (zero meters) defined by the North American Vertical Datum of 1988 (NAVD88). The base contour lines (− 15 m) represent the pre-consolidation heads in the Evangeline aquifer (blue) and the Jasper aquifer (red). The white dashed line represents the 5 mm/year subsidence-contour-line illustrated in Fig. 1 groundwater-level altitude in central and southern Mont- The Lake Houston site is approximately 17  km south gomery County, approximately half of the entire county of Montgomery County. Groundwater levels at the area, is below the pre-consolidation head. A groundwater Lake Houston site will be addressed in the next sec- decline bowl is occurring in The Woodlands area within tion. Since there is little groundwater pumping from both the Evangeline and Jasper aquifers. The Jasper the Burkeville confining unit and the groundwater level groundwater-level altitudes are about − 50  m to − 70  m remained stable during the past decades, no consider- in The Woodlands area, and the Evangeline groundwater- able compaction associated with groundwater pumping level altitude are about from − 60 to − 80 m. is expected in this unit. The pumping from the Catahoula sandstone started in the early 2010s and gradually increased. As of 2018, Groundwater levels in Burkeville confining unit the pumping amount from the Catahoula sandstone was and Catahoula sandstone below 5% of the annual total-pumping in Montgomery The Burkeville confining unit consists primarily of clay, County (Thornhill and Keester 2020). USGS began to which restricts the water flow from the Evangeline monitor groundwater-level in the Catahoula sandstone aquifer to the Jasper aquifer. There are no groundwa - in 2011. There are 13 groundwater-level observation ter-level measurements in the Burkeville confining unit wells in northern Montgomery County (Fig.  5). Figure  9 in Montgomery County before 2020. According to the illustrates the history of Catahoula groundwater levels pumping data from LSGCD, the pumping amount from during the 2010s measured at these 13 wells. In general, the Burkeville confining unit is below 1% of the annual the Catahoula groundwater level has been declining with total-pumping in Montgomery County. GPS and exten an average rate of approximately 1.5  m/year during the someter measurements at the Lake Houston site sug- 2010s. Since the Catahoula sandstone primarily com- gest no considerable groundwater-level changes in the prises consolidated sediments in Miocene and Oligocene, Burkeville confining unit during the past 4  decades. W ang et al. Geoenviron Disasters (2021) 8:28 Page 11 of 24 Fig. 9 Groundwater-level changes in the Catahoula sandstone in northern Montgomery County recorded at 13 wells. The locations of these wells are marked in Fig. 5 no considerable compaction associated with groundwa- in the Chicot aquifer; three wells were completed at dif- ter pumping is expected. ferent depths of the Evangeline aquifer, and one deep well was terminated within the top portion of the Jasper Results aquifer. The borehole of the extensometer was screened Observations at the Lake Houston site at the bottom. The screen allows groundwater to flow In general, GPS-derived subsidence represents the total in and out. Thus, the extensometer borehole (out case) compaction of unconsolidated and semi-consolidated also works as a deep groundwater well measuring the sediments below the land surface. The compaction within groundwater hydraulic head within the top portion of the a specific aquifer is often challenging to ascertain using Burkeville confining unit. HGSD installed a GPS (LKHU) GPS data alone. Combining GPS and long-term bore- antenna on the top of the inner pole in 1993 with the hole extensometer (compaction recorder) datasets may purpose of providing a stable reference for regional land provide compaction information within specific aquifers subsidence monitoring. The inner pole was anchored on (e.g., Yu et  al. 2014; Liu et  al. 2019a, b). Unfortunately, the top of the Burkeville confining unit 591 m below the there are no extensometers in Montgomery County. As land surface (Fig.  10b). A permanent GPS (P009) was of 2020, USGS and HGSD operate 14 borehole exten- installed adjacent to Lake Houston in 1999 (see Fig.  1 someters within the greater Houston region. The clos - for the location). The linear distance between P009 and est extensometer to Montgomery County is located at LKHU is 15 km. Lake Houston, Harris County, approximately 17  km to the south boundary of Montgomery County (Fig. 1). The Evangeline compaction extensometer measurements (1980–2020) are provided Figure 11a depicts the Lake Houston extensometer and by USGS (Ramage and Shah 2019). Land surface eleva- GPS (LKHU) measurements during the past 4 decades. tion at this site is approximately 16  m above mean sea The extensometer measured the total compaction of level. sediments from the land surface to the bottom of the The extensometer borehole at Lake Houston was ter - Evangeline aquifer. The average compaction rate was minated at the top of the Burkeville confining unit, 11.8  mm/year during the 1980s, reduced to 3.8  mm/ 591  m below the land surface (Fig.  10a). Six groundwa- year during the 1990s, and further reduced to approxi- ter observation wells were also installed adjacent to the mately 1.3  mm/year during the 2000s. The GPS meas - extensometer site (Fig.  10b). Two wells were terminated urements (LKHU) on the top of the inner pole indicate Wang et al. Geoenviron Disasters (2021) 8:28 Page 12 of 24 Groundwater wells LKHU Antenna Pole Inner Pole Lake Houston Borehole Extensometer (a)(b) Out Case Fig. 10 a A sketch showing the depths of groundwater wells at the Lake Houston site; b a site photo showing extensometer, GPS, and groundwater wells at the Lake Houston site. The GPS antenna ( TXCN) is mounted on the top of the inner pole of the extensometer, which is anchored at the top of the Burkeville confining unit, 591 m below the land surface no considerable vertical movements during the entire derived from GPS and extensometer datasets agree rea- history from 1993 to 2020. That is, no groundwater- sonably well (− 1.3  mm/year vs . − 1.8  mm/year), which withdrawal-induced aquifer compaction occurred also suggests no considerable compaction below the within the Burkeville confining unit and the Jasper Evangeline aquifer. aquifer at this site. Figure 11b illustrates the groundwater levels recorded GPS-derived subsidence time series at P009 indi- at these seven groundwater-level observation wells. The cates that the ongoing land subsidence (total compac- deep Chicot well (USGS ID: 295451095083901, 165  m tion) rate in this area has been about 1.8 mm/year since below land surface) shows a consistent groundwater- the 2000s. There are tall trees around P009; therefore, level change pattern with these Evangeline groundwa- the scatters of the subsidence time series at P009 are ter levels. It is likely that the groundwater level in this remarkably larger than the scatters at other GPS sites. well was dominated by the groundwater-level change According to the empirical formula (Eq.  1) for estimat- in the Evangeline aquifer. This implies that the inter - ing the accuracy (95% CI) of GPS-derived vertical site face between the Chicot and the Evangeline aquifers at velocities, the two-decadal observations (1999–2020) this site is close to 165  m below the land surface. The would be long enough to secure submillimeter-per- units that make up the Chicot and Evangeline aquifers year accuracy for estimating an overall linear trend are similar in lithology and are difficult to differentiate (subsidence rate) (Wang 2021). The extensometer data (Baker 1979). The Chicot and Evangeline aquifers are indicates that the average subsidence rate during this hydraulically connected, which allows groundwater to period (1999–2020) is approximately 1.3  mm/year. flow between them. The shallow Chicot well (USGS ID: According to an analysis of co-located and closely- 295449095083401, 60  m below land surface) shows a spaced daily-GPS and monthly-extensometer meas- slight rise (0.2 m/year) of the Chicot groundwater level urements at Addicks in northwestern Houston (Wang from approximately − 18 m in 1980 to − 10 m in 2020. et  al. 2014), the root-mean-square (RMS) accuracy of The Chicot groundwater level has been above the pre- the monthly-extensometer measurements is a few mil- consolidation head since the 1990s. It is unlikely that limeters. The accuracy (95% CI) of the compaction rate the Chicot aquifer could considerably contribute to the derived from the 20-year monthly-extensometer data land surface subsidence since the 1990s. Thus, the total (1999–2020) is certainly below 1 mm/year. Considering aquifer compaction recorded by the extensometer dur- the uncertainty of both datasets, the subsidence rates ing the past 3 decades is solely contributed by the com- paction of the Evangeline aquifer. W ang et al. Geoenviron Disasters (2021) 8:28 Page 13 of 24 Fig. 11 Land subsidence and groundwater-level changes at the Lake Houston site. The green box indicates the virgin-compaction phase. The relative locations of wells, extensometer, and GPS are illustrated in Fig. 10. The location of GPS station P009 is marked in Fig. 1 Pre‑consolidation head ′ p = p − u , (2) The correlation between the primary aquifer compac - tion and groundwater-level changes can be explained where p represents effective stress at the grain-to-grain by the Principle of Effective Stress (Terzaghi 1925): contact points within the sediments; p represents total Wang et al. Geoenviron Disasters (2021) 8:28 Page 14 of 24 stress due to the weight of the overlying water and sedi- than the land elevation in southern Harris County, a ments; u represents pore-fluid stress, which is corre - slight hydraulic gradient would occur over the long dis- sponding to the hydraulic head within local sediments. tance from the north to the south. Combining the obser- u can be divided into two parts: a static or equilibrium vations at this site and the pre-consolidation head in head ( u ) in the pore water and a transient pore-water southern Harris County, we deduce that the Evangeline stress ( u ) in excess of the equilibrium pore-water stress. pre-consolidation head in Lake Houston area is approxi- That is, u = u + u . Within aquitards, u decays to zero mately at − 15 to − 25 m, 5 m higher than the pre-consol- w s slowly as water drains from an aquitard and stress equi- idation head in southern Harris County. Determination librium is approached. The total stress ( p ) is also called of the pre-consolidation head will be further discussed in geostatic stress, often regarded as unchanged during the following sections. The long-term static groundwa - multi-decadal to century time scales. The total stress ter hydraulic heads in the two aquifers are approaching ( p ) is balanced by the changes of pore-fluid pressure the same level since the groundwater in the Chicot and ( u ) and effective stress ( p ) exerted on clay particles. the Evangeline aquifers are hydraulically connected. The Pumping causes the reduction of pore-water stress ( u ) pre-consolidation head in the Chicot aquifer would be in response to the declining of the hydraulic head. The the same as the pre-consolidation head in the Evangeline reduced stress will be taken over by the solid grains. The aquifer. maximum effective stress that a lay of sediments had The groundwater level in the extensometer borehole sustained for a long period (century-scale) during its (USGS ID: 295449095084105, completed at 591 m below history is called pre-consolidation stress. When the effec - land surface) was relatively stable during the past 4  dec- tive stress exceeds the pre-consolidation stress, the clay ades, ranging from − 25 to − 35  m (Fig.  11b). Since the grains will undergo significant, permanent rearrange - borehole is terminated within the top of the Burkeville ment, resulting in inelastic (irreversible) compaction. The confining unit, the groundwater level represents the groundwater level corresponding to the pre-consolida- groundwater hydraulic head in the Burkeville confin - tion stress is called the pre-consolidation hydraulic head, ing unit. The thickness of the Burkeville confining unit simply the pre-consolidation head. In the Greater Hou- is approximately 100  m in this area. The GPS antenna ston region, the pre-consolidation head in each aquifer (LKHU) on the inner pole of the extensometer was stable is approximate to the groundwater level before the 1940s over the past 2 decades, indicating no considerable com- when no excessive groundwater pumping occurred. paction within the confining unit. The Evangeline wells indicate that the groundwater The groundwater level in the Jasper well (USGS ID: hydraulic head remained constant during the 1980s, 295449095084101, 790  m below land surface) shows a approximately at − 50 m (Fig. 11b). According to ground- gentle decline from 1980 to 2000 with an average decline water data in the long history illustrated in Fig.  7, rate of 0.5  m/year. A rapid groundwater-level drop of regional-scale groundwater decline began in the 1970s. 10  m occurred within 2  years from 2002 to 2003, which The Evangeline groundwater level started to rise in the did not induce any significant subsidence at the land sur - early 1990s and reached approximately − 35 m at the end face. The Jasper groundwater continued to decline from of 2008. Extensometer measurements indicate that the 2004 to 2014 with an average rate of − 2.5  m/year. The compaction of Evangeline was about 1  mm/year from decline rate slowed down since 2016 with an average 2000 to 2008. The minor subsidence rate suggests that the rate of − 0.6  m/year (2016–2020). The Japer groundwa - groundwater level was approaching the pre-consolidation ter-level altitude declined to − 10  m at the beginning of head. A slight aquifer elastic expansion (or land surface 2020. Since there is no groundwater-withdrawal-induced rebound) is expected if the groundwater level had recov- compaction within the Jasper aquifer as verified by GPS ered to the pre-consolidation head (e.g., Galloway and data (LKHU), the Jasper pre-consolidation head in this Burbey 2011; Liu et al. 2019a; Zhou et al. 2021). Since no area would be lower than the current groundwater level rebound was recorded around this period by the exten- (− 10 m). someter, it is most likely that the Evangeline groundwater level (− 35 m) as of 2008 is still below the pre-consolida- Virgin‑compaction/head‑decline ratio tion head. The aquifer compaction that occurred when the ground - According to the investigations of USGS (e.g., Kas- water level is below the pre-consolidation head is also marek and Robinson 2004; Kasmarek 2012) and UH referred to as virgin compaction in the hydrology litera- (Kearns et  al. 2015, 2019), the pre-consolidation heads ture (e.g., Helm 1975; Galloway and Burbey 2011). The of the Chicot and Evangeline aquifers are approximately increased effective stress that exceeds the maximum his - − 20 to − 30 m in southern Harris County. Since the land toric stress (pre-consolidation stress) during the virgin elevation in the Lake Houston area is about 10 m higher compaction phase is called virgin stress. In this article, W ang et al. Geoenviron Disasters (2021) 8:28 Page 15 of 24 the virgin compaction is specifically referred to as the on the other hand, it is difficult to get the groundwater compaction that occurred when the groundwater level and compaction measurements during the virgin-com- was continuously declining and below the pre-consoli- paction phase. The groundwater levels have been rising dation head, distinguishing it from the compaction that while the land surface is continuously subsiding in the occurred when the groundwater level was stable or rising majority part of northern Harris and Montgomery coun- (see Fig. 11a). ties since the mid-2010s. So, most GPS data are collected The Evangeline wells completed at different depths during the non-virgin-compaction phase. Fortunately, indicate a rapid Evangeline groundwater-level drop of the datasets at Lake Houston provide valuable informa- 5  m from mid-2008.5 to 2013 (Fig.  11b), which resulted tion to delineate the virgin-compaction/head-decline in a compaction of 2  cm within the Evangeline aqui- ratio in the Evangeline aquifer in this region. fer during the period from mid-2009 to 2014 (Fig.  11a). In summary, the long-history of groundwater, exten- Compaction occurs primarily due to the change in pore someter, and GPS datasets at the Lake Houston site have pressure in the clay beds in an aquifer. It takes time for contributed to essential conclusions: (1) groundwater the pressure change in the sand to propagate into the pumping has not induced considerable compactions in clay, for the compaction of clay to occur, and for the deep the Burkeville confining unit and the Jasper aquifer in compaction to propagate to the land surface ultimately. this area; (2) the pre-consolidation head in the Evange- The time lag between groundwater level drop and land line aquifers would be slightly higher than − 30  m, and subsidence occurring at this site is about 1 year. The 5-m the pre-consolidation head in the Jasper aquifer would groundwater-level decline in the Evangeline aquifer led be deeper than − 10 m; (3) the virgin-compaction/head- to a 2-cm virgin-compaction at this site. The ratio of vir - decline ratio in the Evangeline aquifer is approximately gin-compaction to head-decline is approximately 1:250. 1:250 in the Lake Houston area. This ratio is a direct measure of the virgin compressibil - ity of the Evangeline aquifer in this area. The compress - Observations in The Woodlands ibility is related to the geologic age, burial depth, and The Woodlands is located in southern Montgomery content (thickness) of clay layers within the aquifer. The County, 45  km north of Houston. The terrain is essen - Lake Houston site is only 17  km away from Montgom- tially flat, ranging from 40 to 60  m above sea level. The ery County. According to USGS investigations (e.g., Kas- Woodlands is one of the fastest-growing suburban areas marek and Robinson 2004), the clay layers within the top in Texas. Groundwater pumping has increased signifi - aquifers (Chicot, Evangeline, upper Jasper) are similar on cantly since the 2000s. both sides of the boundary between Harris and Mont- gomery counties. Evangeline virgin‑compaction/head‑decline ratio In practice, it is a challenge to estimate the virgin com- Figure  12a shows the locations of six GPS stations pressibility of an aquifer. On the one hand, it is often diffi - and three sets of closely-spaced Evangeline and Jasper cult to measure the compaction within a specific aquifer; groundwater wells in The Woodlands area. Figure  12b, c (a) (b) (c) P013 WHCR Fig. 12 a Map showing the locations of GPS and groundwater-level observation wells in The Woodlands area; b the permanent GPS antenna pole and solar power system at P013; c GPS antenna WHCR, which is located in The Woodlands High School. The LiDAR data for plotting the DEM map is available at NOAA (https:// coast. noaa. gov/ datav iewer) Wang et al. Geoenviron Disasters (2021) 8:28 Page 16 of 24 show site views at GPS stations P013 and WHCR. P013 is are in a none-virgin-compaction phase. The compress - a typical PAM station installed on the free field. WHCR ibility of each aquifer during the non-virgin-compaction is a typical UH GPS station installed on school buildings. phase could be differ from the compressibility during the GSEC, PWES, and WHCR are installed on single-story virgin-compaction phase. school buildings in Galatas Elementary School, Powell Elementary School, and The Woodlands High School. Jasper pre‑consolidation head Figure  13a depicts the GPS-derived land subsidence GPS-derived subsidence at P013 shows a reduction of time series at these GPS sites. GPS-derived subsidence the subsidence rate in the middle of 2004. The subsid - time series at these six sites consistently suggest that the ence rate was 11  mm/year from 2001 to 2003, which is average rate of ongoing subsidence (2016–2020) in this comparable to the rate that could be produced by the area is approximately 7–8  mm/year. P013 has a history compaction of the Evangeline aquifer alone (~ 10  mm/ of 2  decades (2000–2020) and shows the occurrence of year) with the groundwater hydraulic head decline rate of an acceleration of subsidence in the middle of 2004. The 2.4  m/year. There were no substantial groundwater-level subsidence rate changed from 11 mm/year (2001–2004.5) changes in the Evangeline aquifer around 2004. So, the to 16  mm/year (2005–2015). There has been a decelera - increased subsidence rate (from 11 to 16 mm/year) might tion of subsidence since 2016. The Woodlands area began be primarily contributed by the additional compaction of receiving surface water from Lake Conroe in 2015. Sub- the Jasper aquifer. In other words, the compaction of the sequently, land subsidence reduced from 16  mm/year Jasper aquifer likely began in 2004. The Jasper groundwa - (2005–2015) to 8 mm/year (2016–2020). ter level in 2004 would be close to the pre-consolidation Figure  13b depicts the history of groundwater-level head of the Jasper aquifer. Figure  13b indicates that the changes in The Woodland area. Measurements at three Jasper groundwater-level altitude in 2004 was approxi- Evangeline wells indicate that the Evangeline ground- mately − 25  m. The observations at the Lake Houston water-level altitude was below the pre-consolidation site already concluded that the pre-consolidation head head and declined with a steady rate of 2.4 m/year from in the Jasper aquifer must be below − 10  m. It is very 2001 to 2014. The groundwater level began to rise after likely that the pre-consolidation head in the Jasper aqui- the surface water was available for municipal use since fer is between − 15 and − 25  m, which is similar to the approximately 2015. The observations at the Lake Hou - pre-consolidation heads in the Chicot and Evangeline ston site have suggested that the Evangeline virgin-com- aquifers in this area. The land elevation at P013 is approx - paction/head-decline ratio in this area is about 1:250 imately 50  m above sea level. The Jasper pre-consolida - (Fig.  11). The groundwater-level decline of 2.4  m/year tion head in this area would be 65–75 m below the land in the Evangeline aquifer would result in a compaction surface. approximately 10  mm/year. GPS measurements at P013 In summary, the observations at The Woodlands sug - indicate that the total compaction rate was 16  mm/ gest: (1) the compaction in the Jasper aquifer began in year from 2004 to 2015. The compactions of the Chicot the mid-2000s in The Woodlands area and contributed aquifer and the Burkeville confining unit are ignorable, to approximately one-third of the land subsidence from as previously discussed. That means the compaction of the mid-2000s to mid-2010s; (2) the pre-consolidation the Jasper aquifer resulted in the remaining 6  mm/year. head of the Jasper aquifer is approximately at − 15 to The measurements at three Jasper wells closely-spaced − 25  m; (3) the virgin-compaction/head-decline ratio in with these three Evangeline wells indicate that the Jasper the Jasper aquifer is approximately 1:800 in Montgomery groundwater-level decline rate was approximately 4.8 m/ County. year from 2004 to 2014. Accordingly, the virgin-compac- tion/head-decline ratio in the Jasper aquifer in this area is Observations in the City of Conroe approximately 1:800. That is, the Jasper Aquifer is three The City of Conroe is the county seat, the economic to four times less susceptible to compaction than the and geographic center of Montgomery  County (Fig.  5). overlying Evangeline aquifer in this area. Figure  14a depicts four permanent GPS stations, three The groundwater level and GPS datasets also suggest Chicot wells, one Evangeline well, and six Jasper wells that the Jasper aquifer contributed approximately one- in the Conroe area. Figure  14b shows a site photo at the third of the total compaction (6 of 16  mm/year) from GPS antenna TXCN, mounted on the roof of the office 2005 to 2015. Unfortunately, it is difficult to distinguish building of TxDOT at Conroe. Figure 15 illustrates GPS- the contribution of the Jasper aquifer from the land sub- derived subsidence and groundwater level changes dur- sidence (total compaction) since 2016. Groundwater lev- ing the past 2  decades. TXCN (2004–2020) recorded els in both the Jasper and Evangeline aquifers have been steady subsidence from 2007 to 2015 with an average rate rising since 2016. The ongoing compactions since 2016 of − 14  mm/year. The subsidence rate has been reduced W ang et al. Geoenviron Disasters (2021) 8:28 Page 17 of 24 Fig. 13 GPS-derived subsidence and groundwater levels in The Woodland area. The locations of these wells and GPS are marked in Fig. 12 Wang et al. Geoenviron Disasters (2021) 8:28 Page 18 of 24 (b) (a) TXCN Fig. 14 a Map showing the locations of GPS stations and groundwater-level observation wells in the Conroe area; b GPS antenna TXCN, mounted on the roof of the Texas Department of Transportation office building in the City of Conroe, Montgomery County. The LiDAR data for plotting the DEM map is available at NOAA (https:// coast. noaa. gov/ datav iewer) to 6  mm/year since 2016. Observations at other three groundwater levels in all aquifers (Chicot, Evangeline, GPS stations (UH02, P070, P071) also suggest that the Jasper) were above their pre-consolidation heads (− 15 to ongoing subsidence rate is approximately 6  mm/year − 25 m). in this area (Fig.  15a). There is only one Evangeline well In summary, the compaction of the Evangeline aqui- (USGS ID: 301614095284201, terminated 216  m below fer began in the early 2000s in the Conroe area, and the land surface) in the Conroe area, which indicates a compaction of the Jasper aquifer began in the mid-2000s. groundwater level decline rate of 2.7 m/year (2004–2013) The Jasper compaction contributed approximately one- (Fig.  15b). The Jasper groundwater level declined with third of the total compaction (subsidence) from 2007 to a rate of 3.2  m/year during the same period. The 2.7  m/ 2015. The observations in the Conroe area confirmed year groundwater-level decline in the Evangeline aquifer that the estimates of pre-consolidation heads and virgin- would lead to subsidence of approximately 11  mm/year compaction/head-decline ratios in the Evangeline and based on the virgin-compress/head-decline ratio of 1:250; Jasper aquifers are reasonable. the 3.2 m/year groundwater-level drop in the Jasper aqui- fer will lead to subsidence of approximately 4  mm/year Observations in the Southeast area based on the virgin-compress/head-decline ratio of 1:800. Figure 16 depicts land subsidence and groundwater-level The total subsidence rate would be about 15  mm/year. changes in southeastern Montgomery County and adja- GPS station TXCN did record land surface subsidence of cent areas. Locations of groundwater-level observation 14 mm/year during this period (2007–2015). The analyti - wells and GPS are marked in Fig.  5. GPS station P072 cal solution (15  mm/year) and the direct measurement is in the New Caney area. P012 is next to the southeast (14  mm/year) agree with each other, which further veri- border of Montgomery County, adjacent to Kingwood, fies that the estimated virgin-compaction/head-decline the largest master-planned residential community in ratios are reasonable. northern Harris County and southern Montgomery The groundwater level in the Jasper aquifer declined County. COH6 and P065 are two GPS stations in Harris to below − 25  m in the early 2006. GPS-derived subsid- County, approximately 5  km from Montgomery County. ence time series at TXCN indicated a rapid drop of the GPS-derived subsidence at these four sites indicates that land surface at the end of 2006 (Fig.  15a). The additional the ongoing subsidence since the 2010s in southeastern compaction of the Jasper aquifer possibly caused the Montgomery County is about 5–8  mm/year (Fig.  16a). increased subsidence rate. So, − 25 m is a reasonable esti- The Evangeline groundwater level was stable and close mate of the lower bound of the pre-consolidation head to the pre-consolidation head during past 3  decades in the Jasper aquifer. According to the declining trend of (Fig. 16b). the Evangeline groundwater, the Evangeline groundwa- The Jasper well at the eastern border (USGS ID: ter level in the Conroe area was above the pre-consoli- 301911095092901), near Cleveland, indicates that the dation before 2000. In other words, land subsidence in Jasper groundwater level has been declining over its the Conroe area would be minor before 2000 since the entire history since the 1990s and is still above the W ang et al. Geoenviron Disasters (2021) 8:28 Page 19 of 24 Fig. 15 GPS-derived land subsidence and groundwater-level changes in Conroe area. The locations of these wells and GPS are marked in Fig. 14 Wang et al. Geoenviron Disasters (2021) 8:28 Page 20 of 24 Fig. 16 GPS-derived land subsidence and groundwater levels in southeastern Montgomery County. The locations of GPS stations and groundwater wells are marked in Fig. 5 W ang et al. Geoenviron Disasters (2021) 8:28 Page 21 of 24 pre-consolidation head as of 2020 (Fig.  16c). The Jasper also approximately one-third of the land subsidence well near Splendora (USGS ID: 301443095091801) indi- (6 mm/year vs. 15–20 mm/year) during the virgin com- cates that the Jasper groundwater has been approach- paction phase. Both the Evangeline and Jasper ground- ing the pre-consolidation head since the mid-2010s. The water-level altitudes are approximately 30  m below Jasper well (USGS ID: 301016095165501) close to P012 their pre-consolidation heads as of 2020. Land subsid- shows that the Jasper groundwater level declined to the ence will continue until groundwater levels in both the pre-consolidation head in 2006 and reached the lowest Evangeline and Jasper aquifers recover to their pre-con- level in 2014. The Jasper groundwater level began to rise solidation heads. in 2015 following the reduction of groundwater pumping. The average decline rate of the Jasper groundwater level was approximately 5.0 m/year (2004–2014), which would Discussion produce approximately 6 mm/year compaction according Land subsidence is probably one of the most evident to the virgin-compaction/head-decline ratio of 1:800. The environmental effects of excessive groundwater pump - analytical compaction rate of 6  mm/year within the Jas- ing. The GPS-derived positional time series presented in per aquifer is comparable with the total compaction rates this study suggest that the rate of subsidence varies con- (5–8 mm/year) recorded by GPS in this area. That is, the siderably over time and space, depending on groundwa- ongoing land subsidence in this area is dominated by the ter levels and the changes of groundwater levels in both compaction of the Jasper aquifer. This result is consistent the Evangeline and Jasper aquifers. A remarkable reduc- with the fact that the Chicot and Evangeline groundwater tion of the subsidence rate has been recorded by GPS levels were above their pre-consolidation head during the in central and southern Montgomery County since the past 2 decades (Fig. 16b). mid-2010s due to the reduction of pumping as a result of In summary, the observations in southeastern Mont- groundwater regulation. The observations presented in gomery County indicate that land subsidence in this this study reveal that land subsidence is a human-induced area is dominated by the compaction of the Jasper aqui- “natural” hazard depending on how groundwater is man- fer since the late 2000s. The observations further con - aged and regulated. firm that the estimates of regional pre-consolidation LSGCD adjusted its groundwater regulation rules in heads and the virgin-compaction/head-decline ratios are 2020. The 2020 regulatory plan no longer requires the reasonable. large volume groundwater users to follow the previous rule of reducing their groundwater production by thirty percent (30%) of their Total Qualifying Demand (LSGCD Observations in the Southwest area 2020). It is likely that the groundwater levels in Mont- Figure  17 illustrates GPS-derived subsidence and gomery County, as well as in its neighboring counties, groundwater-level changes in southwestern Mont- will further decline in the future. As of 2020, the Jasper gomery County. Locations of these GPS stations and groundwater-level altitude is approximately 20–40  m groundwater wells are marked in Fig.  5. GPS sta- below the pre-consolidation head in central and southern tions P017 and ROD1 are located in northern Harris Montgomery County; the Evangeline groundwater-level County, approximately 5  km to Montgomery County. altitude is about 40–60  m below the pre-consolidation GPS measurements at P017 indicate that the subsid- head in southern Montgomery County. Subsidence will ence rate was up to 2  cm/year during the 2000s and continue to occur as long as the groundwater hydrau- slowed down since the mid-2010s. The ongoing subsid - lic head in either the Evangeline or the Jasper aquifer ence in this area is about 7–12  mm/year (2015–2020) remains below its pre-consolidation head. (Fig. 17a). The Chicot groundwater level was stable and GPS and groundwater monitoring datasets in Mont- above the pre-consolidation during the past 3 decades. gomery County provide first-hand information for The Evangeline groundwater level declined to below the tracking land subsidence and understanding the cause- pre-consolidation head in the late 1990s and retained and-effect relationship in groundwater-level changes and stable during the 2010s (Fig.  17b). The Jasper ground - aquifer compactions. By 2020, subsidence over 5  mm/ water level declined to the pre-consolidation head in year is ongoing in central and southern Montgomery the mid-2000s and retained stable during the 2010s County, approximately half the area of the entire county. (Fig.  17c). The Jasper groundwater level declined with Continuously conducting county-wide groundwater- a rate of 5  m/year during the virgin-compaction phase level and land subsidence monitoring is essential for (2005–2010). According to the virgin-compaction/ understanding the temporospatial progress of subsid- head-decline ratio of 1:800, the 5  m/year head-decline ence and for future groundwater supply planning and would result in approximately 6  mm/year of compac- management. tion. The contribution of the Jasper compaction was Wang et al. Geoenviron Disasters (2021) 8:28 Page 22 of 24 Fig. 17 GPS-derived land subsidence and groundwater levels in southwestern Montgomery County. The locations of GPS stations and groundwater wells are marked in Fig. 5 W ang et al. Geoenviron Disasters (2021) 8:28 Page 23 of 24 Received: 17 June 2021 Accepted: 20 October 2021 Conclusions Based on the long-term groundwater level and land subsidence observations in the Montgomery County and northern Harris County, we conclude that: References Agudelo G, Wang G, Liu Y, Bao Y, Turco MJ (2020) GPS geodetic infrastructure (1) the pre-consolidation heads of the three aquifers for subsidence and fault monitoring in Houston, Texas, USA. Proc Int Assoc Hydrol 382:11–18 in the Montgomery County area are close to each Baker ET, Jr (1979) Stratigraphic and hydrogeologic framework of part of the other, approximately 15–25 m below sea level; coastal plain of Texas. Texas Department of Water Resources Report 236, (2) the compactions from the Chicot aquifer and the p 43 Braun CL, Ramage JK (2020) Status of groundwater-level altitudes and long- Burkeville confining unit during the past 3 decades term groundwater-level changes in the Chicot, Evangeline, and Jasper would be minor even if they did occur; aquifers, Houston-Galveston region, Texas, 2020. U.S. Geological Survey (3) the ongoing subsidence in Montgomery County Scientific Investigations Report 2020–5089, p 18 Campbell MD, Campbell MD, Wise HM (2018) Growth faulting and subsidence since the mid-2000s has been dominated by the in the Houston, Texas area: guide to the origins, relationships, hazards, compactions of the Evangeline and Jasper aquifers; potential impacts and methods of investigation: an update. J Geol Geosci (4) the compaction of the Jasper aquifer began in the 2:1–53 Casarez IR (2020) Aquifer extents in the coastal lowlands aquifer system mid-2000s in The Woodlands and Conroe areas and regional groundwater availability study area in Texas, Louisiana, Missis- contributed about one-third of the land subsidence sippi, Alabama, and Florida. U.S. Geological Survey data release. https:// since the mid-2000s; doi. org/ 10. 5066/ P9BH2 KG2 Chowdhury AH, Turco MJ (2006) Geology of the Gulf coast aquifer, Texas. Texas (5) the virgin-compaction/head-decline ratio is approx- Water Dev Board Rep 365:23–50 imately 1:250 in the Evangeline aquifer and 1:800 in Coplin LS, Galloway D (1999) Houston-Galveston, Texas. Land subsidence in the Jasper aquifer in central and southern Mont- the United States. US Geol Surv Circ 1182:35–48 Furnans J, Keester M, Colvin D, Bauer J, Barber J, Gin G, Danielson V, Erickson L, gomery County. Ryan R, Khorzad K, Worsley A, Snyder G (2018) Final report: identification of the vulnerability of the major and minor aquifers of Texas to subsid- ence with regard to groundwater pumping. Texas Water Development Acknowledgements Board, Contract report No. 1648302062, p 434 The authors acknowledge LSGCD, HGSD, USGS, TxDOT, SmartNet, and Gabrysch RK (1967) Development of ground water in the Houston district, UNAVCO for archiving and sharing groundwater and GPS data with the public. Texas, 1961–65. Texas Water Dev Board Rep 63:35 The authors acknowledge the comments and suggestions from Mr. Michael R. Galloway DL, Burbey TJ (2011) Review: regional land subsidence accompany- Keester (LRE water) and two anonymous reviewers. Figs. 1, 4, 5, 8, 12a, and 14a ing groundwater extraction. Hydrogeol J 19:1459–1486 are generated using the Generic Mapping Tools (GMT ), developed by Wessel Greuter A, Petersen P (2021) Determination of groundwater withdrawal and et al. (2013). subsidence in Harris and Galveston counties—2020. Harris-Galveston Subsidence District Report. https:// hgsub siden ce. org/ wp- conte nt/ uploa Authors’ contributions ds/ 2021/ 05/ 2020- HGSD- AGR_ Full- Report- 1. pdf K.W. and G.W. processed data and prepared the draft. B.C., H.L., and Y.B. Helm DC (1975) One-dimensional simulation of aquifer system compaction analyzed data, reviewed, and edited the manuscript. All authors read and near Pixley, Calif.: 1. constant parameters. Water Resour Res 11(3):465–478 approved the final manuscript. Kasmarek MC (2012) Hydrogeology and simulation of groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer Funding system, Texas, 1891–2009 (ver. 1.1, December 2013). U.S. Geological Hanlin Lius’s contribution to this work was supported by the National Key R&D Survey Scientific Investigations Report 2012–5154, p 55 Program of China (No. 2019YFB2102700); Yan Bao’s contribution to this work Kasmarek MC, Robinson JL (2004) Hydrogeology and simulation of ground- was supported by National Science Foundation of China (No. 51829801). water flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system, Texas. U.S. Geological Survey Scientific Investiga- Availability of data and materials tions Report 2004–5102, p 111 GPS raw data used for this study are available at HGSD (https:// hgsub siden Kasmarek MC, Ramage JK, Johnson MR (2016) Water-level altitudes 2016 and ce. org), UNAVCO (https:// www. unavco. org), and NGS (https:// www. ngs. noaa. water-level changes in the Chicot, Evangeline, and Jasper aquifers and gov/ CORS). The groundwater measurements are available at USGS (https:// compaction 1973–2015 in the Chicot and Evangeline aquifers, Houston- water data. usgs. gov/ nwis). All processed data, models, or code that sup- Galveston region, Texas. U.S. Geological Survey Scientific Investigations port the findings of this study are available from the corresponding author Map 3365, pamphlet, 16 sheets, scale 1:100,000 (gwang@uh.edu) upon request. Kearns TJ, Wang G, Bao Y, Jiang J, Lee D (2015) Current land subsidence and groundwater level changes in the Houston metropolitan area Declaration (2005–2012). J Surv Eng 141(4):05015002 Kearns TJ, Wang G, Turco MJ, Welch J, Tsibanos V, Liu H (2019) Houston16: a Competing interests stable geodetic reference frame for subsidence and faulting study in the The authors declare no conflict of interest. Houston metropolitan area, Texas. US Geod Geodyn 10(5):382–393 Kelley V, Deeds N, Young SC, Pinkard J, Sheng Z, Seifert J, Marr S (2018) Subsid- Author details ence risk assessment and regulatory considerations for the brackish Department of Earth and Atmospheric Sciences, University of Houston, Jasper aquifer—Harris-Galveston and Fort Bend Subsidence Districts. Houston 77204, USA. Institute of Urban Smart Transportation and Safety Report prepared for Harris-Galveston Subsidence District and Fort Bend Maintenance, Shenzhen University, Shenzhen 518060, China. K ey Laborator y Subsidence District, p 69 of Urban Security and Disaster Engineering of Ministry of Education, Beijing Khan SD, Stewart RR, Otoum M, Chang L (2013) A geophysical investigation University of Technology, Beijing 100029, China. of the active Hockley fault system near Houston, Texas. Geophysics 78:B177–B185 Wang et al. Geoenviron Disasters (2021) 8:28 Page 24 of 24 Liu Y, Li J, Fang Z (2019a) Groundwater level change management on control Wang G, Soler T (2014) Measuring land subsidence using GPS: ellipsoid height of land subsidence supported by borehole extensometer compaction vs. orthometric height. J Surv Eng 141:05014004 measurements in the Houston-Galveston region. Texas Geosci 9(5):223 Wang G, Yu J, Ortega J, Saenz G, Burrough T, Neill R (2013) A stable reference Liu Y, Sun X, Wang G, Turco MJ, Agudelo G, Bao Y, Zhao R, Shen S (2019b) frame for the study of ground deformation in the Houston metropolitan Current activity of the Long Point fault in Houston, Texas constrained by area, Texas. J Geod Sci 3:188–202 continuous GPS measurements (2013–2018). Remote Sens 11(10):1213 Wang G, Yu J, Kearns TJ, Ortega J (2014) Assessing the accuracy of long-term LSGCD (2013) Lone Star Groundwater Conservation District Management subsidence derived from borehole extensometer data using GPS obser- Plan—re-adopted November 12, 2013. https:// www. lones targcd. org/ vations: case study in Houston, Texas. J Surv Eng 140(3):05014001 distr ict- rules-1 Wang G, Welch J, Kearns T, Yang L, Serna J Jr (2015) Introduction to GPS LSGCD (2020) 2020 Lone Star Groundwater Conservation District Manage- geodetic infrastructure for land subsidence monitoring in Houston, Texas, ment Plan, as approved on May 15, 2020. https:// www. lones targcd. org/ USA. Proc Int Assoc Hydrol Sci 372:297–303 distr ict- rules-1 Wang G, Turco M, Soler T, Kearns TJ, Welch J (2017) Comparisons of OPUS and Miller MM, Shirzaei M (2019) Land subsidence in Houston correlated with PPP solutions for subsidence monitoring in the greater Houston area. J flooding from Hurricane Harvey. Remote Sens Environ 225:368–378 Surv Eng 143(4):05017005 Petersen C, Turco MJ, Vinson A, Turco JA, Petrov A, Evans M (2020) Ground- Wang G, Zhou X, Wang K, Ke X, Zhang Y, Zhao R, Bao Y (2020) GOM20: a stable water regulation and the development of alternative source waters to geodetic reference frame for subsidence, faulting, and sea-level rise stud- prevent Subsidence, Houston region, Texas, USA. Proc IAHS 382:797–801 ies along the Coast of the Gulf of Mexico. Remote Sens 12(3):350 Popkin BP (1971) Groundwater resources of Montgomery County, Texas. Texas Welch J (2018) Current ground motions in Montgomery, West Liberty, and Water Dev Board Rep 136:143 Northern Harris counties derived from continuous GPS motions. Mather Qu F, Lu Z, Zhang Q, Bawden GW, Kim J, Zhao C, Qu W (2015) Mapping ground Thesis, Department of Earth and Atmospheric Sciences, University of deformation over Houston-Galveston, Texas using multi-temporal InSAR. Houston Remote Sens Environ 169:290–306 Wessel P, Smith WHF, Scharroo R, Luis J, Wobbe F (2013) Generic map- Qu F, Lu Z, Kim JW, Zheng W (2019) Identify and monitor growth faulting ping tools: improved version released. EOS Trans Am Geophys Union using InSAR over northern greater Houston, Texas, USA. Remote Sens 94(45):409–410 11(12):1498 Young SC, Ewing T, Hamlin S, Baker E, Lupton D (2012) Final report—updating Ramage JK (2020) Depth to groundwater measured from wells completed in the hydrogeologic framework for the northern portion of the gulf coast the Chicot, Evangeline, and Jasper aquifers, Houston-Galveston region, aquifer. Contract report for the Texas Water Development Board, p 285 Texas, 2020. U.S. Geological Survey data release Young SC, Jigmond M, Deeds N, Blainey J, Ewing TE, Banerj D, Piemonti D, Ramage JK, Shah SD (2019) Cumulative compaction of subsurface sediments Jones T, Griffith C, Lupton D, Martinez G, Hudson C, Hamlin S, Sutherland in the Chicot and Evangeline aquifers in the Houston-Galveston region, J (2016) Final report: identification of potential brackish groundwater Texas (ver. 2.0, June 2020). U.S. Geological Survey data release production areas—Gulf Coast Aquifer System. Contract report to the Shah SD, Ramage JK, Braun CL (2018) Status of groundwater-level altitudes Texas Water Development Board, p 636 and long-term groundwater-level changes in the Chicot, Evangeline, and Yu J, Wang G, Kearns TJ, Yang L (2014) Is there deep-seated subsidence in the Jasper aquifers, Houston-Galveston region, Texas, 2018. U.S. Geological Houston-Galveston area. J Geophys 942834:1–11 Survey Scientific Investigations Report 2018–5101, p 18 Zhou F (2020) The correlation between current land subsidence and ground- Terzaghi K (1925) Principles of soil mechanics: I-Phenomena of cohesion of water levels in Montgomery County, Texas. Mather Thesis, Department of clays. Eng News-Rec 95(19):742–746 Earth and Atmospheric Sciences, University of Houston Thornhill MR, Keester MR (2020) Subsidence investigations—phase 1: assess- Zhou X, Wang G, Wang K, Liu H, Lyu H, Turco MJ (2021) Rates of natural subsid- ment of past and current investigations, prepared for Lone Star Ground- ence and submergence along the Texas coast derived from GPS and tide water Conservation District. https:// www. lones targcd. org/ subsi dence gauge measurements (1904–2020). J Surv Eng 147(4):04021020 Turco MJ, Petrov A (2015) Eec ff ts of groundwater regulation on aquifer-system compaction and subsidence in the Houston-Galveston Region, Texas, Publisher’s Note USA. Proc Int Assoc Hydrol Sci 372:511–514 Springer Nature remains neutral with regard to jurisdictional claims in pub- Wang G (2021) The 95% confidence interval for the GNSS-derived site veloci- lished maps and institutional affiliations. ties. J Surv Eng. https:// doi. org/ 10. 1061/ (ASCE) SU. 1943- 5428. 00003 90

Journal

Geoenvironmental DisastersSpringer Journals

Published: Oct 31, 2021

Keywords: Subsidence; Pumping; GPS; Pre-consolidation head; Virgin-compaction/head-decline ratio

There are no references for this article.