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Michelle Sneed

Publications and source records attributed to Michelle Sneed.

At least 37 records · Page 2Linked to original sources
USGS2015

Hydrogeology, hydrologic effects of development, and simulation of groundwater flow in the Borrego Valley, San Diego County, California

Executive Summary The Borrego Valley is a small valley (110 square miles) in the northeastern part of San Diego County, California. Although the valley is about 60 miles northeast of city of San Diego, it is separated from the Pacific Ocean coast by the mountains to the west and is mostly within the boundaries of Anza-Borrego Desert State Park. From the time the basin was first settled, groundwater has been the only source of water to the valley. Groundwater is used for agricultural, recreational, and municipal purposes. Over time, groundwater withdrawal through pumping has exceeded the amount of water that has been replenished, causing groundwater-level declines of more than 100 feet in some parts of the basin. Continued pumping has resulted in an increase in pumping lifts, reduced well efficiency, dry wells, changes in water quality, and loss of natural groundwater discharge. As a result, the U.S. Geological Survey began a cooperative study of the Borrego Valley with the Borrego Water District (BWD) in 2009. The purpose of the study was to develop a greater understanding of the hydrogeology of the Borrego Valley Groundwater Basin (BVGB) and to provide tools to help evaluate the potential hydrologic effects of future development. The objectives of the study were to (1) improve the understanding of groundwater conditions and land subsidence, (2) incorporate this improved understanding into a model that would assist in the management of the groundwater resources in the Borrego Valley, and (3) use this model to test several management scenarios. This model provides the capability for the BWD and regional stakeholders to quantify the relative benefits of various options for increasing groundwater storage. The study focuses on the period 1945–2010, with scenarios 50 years into the future. This report documents and presents (1) an analysis of the conceptual model, (2) a description of the hydrologic features, (3) a compilation and analysis of water-quality data, (4) the measurement and analysis of land subsidence by using geophysical and remote sensing techniques, (5) the development and calibration of a two-dimensional borehole-groundwater-flow model to estimate aquifer hydraulic conductivities, (6) the development and calibration of a three-dimensional (3-D) integrated hydrologic flow model, (7) a water-availability analysis with respect to current climate variability and land use, and (8) potential future management scenarios. The integrated hydrologic model, referred to here as the “Borrego Valley Hydrologic Model” (BVHM), is a tool that can provide results with the accuracy needed for making water-management decisions, although potential future refinements and enhancements could further improve the level of spatial and temporal resolution and model accuracy. Because the model incorporates time-varying inflows and outflows, this tool can be used to evaluate the effects of temporal changes in recharge and pumping and to compare the relative effects of different water-management scenarios on the aquifer system. Overall, the development of the hydrogeologic and hydrologic models, data networks, and hydrologic analysis provides a basis for assessing surface and groundwater availability and potential water-resource management guidelines.

California↗
USGS2015

Water availability and land subsidence in the Central Valley, California, USA

The Central Valley in California (USA) covers about 52,000 km 2 and is one of the most productive agricultural regions in the world. This agriculture relies heavily on surface-water diversions and groundwater pumpage to meet irrigation water demand. Because the valley is semi-arid and surface-water availability varies substantially, agriculture relies heavily on local groundwater. In the southern two thirds of the valley, the San Joaquin Valley, historic and recent groundwater pumpage has caused significant and extensive drawdowns, aquifer-system compaction and subsidence. During recent drought periods (2007–2009 and 2012-present), groundwater pumping has increased owing to a combination of decreased surface-water availability and land-use changes. Declining groundwater levels, approaching or surpassing historical low levels, have caused accelerated and renewed compaction and subsidence that likely is mostly permanent. The subsidence has caused operational, maintenance, and construction-design problems for water-delivery and flood-control canals in the San Joaquin Valley. Planning for the effects of continued subsidence in the area is important for water agencies. As land use, managed aquifer recharge, and surface-water availability continue to vary, long-term groundwater-level and subsidence monitoring and modelling are critical to understanding the dynamics of historical and continued groundwater use resulting in additional water-level and groundwater storage declines, and associated subsidence. Modeling tools such as the Central Valley Hydrologic Model, can be used in the evaluation of management strategies to mitigate adverse impacts due to subsidence while also optimizing water availability. This knowledge will be critical for successful implementation of recent legislation aimed toward sustainable groundwater use.

California↗
USGS2015

Land subsidence in the San Joaquin Valley, California, USA, 2007-14

Rapid land subsidence was recently measured using multiple methods in two areas of the San Joaquin Valley (SJV): between Merced and Fresno (El Nido), and between Fresno and Bakersfield (Pixley). Recent land-use changes and diminished surface-water availability have led to increased groundwater pumping, groundwater-level declines, and land subsidence. Differential land subsidence has reduced the flow capacity of water-conveyance systems in these areas, exacerbating flood hazards and affecting the delivery of irrigation water. Vertical land-surface changes during 2007–2014 were determined by using Interferometric Synthetic Aperture Radar (InSAR), Continuous Global Positioning System (CGPS), and extensometer data. Results of the InSAR analysis indicate that about 7600 km 2 subsided 50–540 mm during 2008–2010; CGPS and extensometer data indicate that these rates continued or accelerated through December 2014. The maximum InSAR-measured rate of 270 mm yr −1 occurred in the El Nido area, and is among the largest rates ever measured in the SJV. In the Pixley area, the maximum InSAR-measured rate during 2008–2010 was 90 mm yr −1 . Groundwater was an important part of the water supply in both areas, and pumping increased when land use changed or when surface water was less available. This increased pumping caused groundwater-level declines to near or below historical lows during the drought periods 2007–2009 and 2012–present. Long-term groundwater-level and land-subsidence monitoring in the SJV is critical for understanding the interconnection of land use, groundwater levels, and subsidence, and evaluating management strategies that help mitigate subsidence hazards to infrastructure while optimizing water supplies.

California↗
USGS2015

Lithostratigraphic, borehole-geophysical, hydrogeologic, and hydrochemical data from the East Bay Plain, Alameda County, California

The U.S. Geological Survey, in cooperation with the East Bay Municipal Utility District, carried out an investigation of aquifer-system deformation associated with groundwater-level changes at the Bayside Groundwater Project near the modern San Francisco Bay shore in San Lorenzo, California. As a part of the Bayside Groundwater Project, East Bay Municipal Utility District proposed an aquifer storage and recovery program for 1 million gallons of water per day. The potential for aquifer-system compaction and expansion, and related subsidence, uplift, or both, resulting from aquifer storage and recovery activities were investigated and monitored in the Bayside Groundwater Project. In addition, baseline analysis of groundwater and substrata properties were performed to assess the potential effect of such activities. Chemical and physical data, obtained from the subsurface at four sites on the east side of San Francisco Bay in the San Lorenzo and San Leandro areas of the East Bay Plain, Alameda County, California, were collected during the study. The results of the study were provided to the East Bay Municipal Utility District and other agencies to evaluate the chemical and mechanical responses of aquifers underlying the East Bay Plain to the future injection and recovery of imported water from the Sierra Nevada of California. Among 4 sites, 14 piezometers and 2 extensometers were installed in 6 boreholes, which ranged in depth from 460 to 1,040 feet. The lithology of drill cuttings, collected at 5- or 10-foot intervals, was described for grain size and any other noticeable features, such as wood or shell fragments. Borehole geophysical logging was performed at each site in the deepest borehole, immediately following drilling. Drill-core samples, totaling 284 feet, were collected at the Bayside site. The drill-core sediment was subsampled to determine pore-water chemistry, vertical hydraulic conductivity, and physical and mechanical properties at different depths. Depositional environment and age were determined by luminescence geochronology and fossil identification. The elemental composition of the drill-core sediments was determined by inductively coupled plasma mass spectroscopy and instrumental neutron activation by abbreviated count analysis. Mineral composition was determined by X-ray diffraction and scanning electron microscopy analysis. Groundwater samples were collected from all 14 piezometers as part of either the USGS Groundwater Ambient Monitoring and Assessment or the USGS National Water Quality Assessment program for water-quality analyses. Sample analytes included nutrients, major and minor ions, trace elements, isotopic ratios of hydrogen and oxygen in water, carbon-14, and tritium. Water-level and aquifer-system-compaction measurements, which indicated diurnal and seasonal fluctuations, were made at the Bayside Groundwater Project site. Slug tests were performed at the Bayside piezometers and nine pre-existing wells to estimate hydraulic conductivity.

California↗
USGS2014

Subsidence (2004-2009) in and near lakebeds of the Mojave River and Morongo groundwater basins, southwest Mojave Desert, California

Subsidence, in the vicinity of dry lakebeds, within the Mojave River and Morongo groundwater basins of the southwest Mojave Desert has been measured by Interferometric Synthetic Aperture Radar (InSAR). The investigation has focused on determining the location, extent, and magnitude of changes in land-surface elevation. In addition, the relation of changes in land-surface elevation to changes in groundwater levels and lithology was explored. This report is the third in a series of reports investigating land-surface elevation changes in the Mojave and Morongo Groundwater Basins, California. The first report, U.S. Geological Survey (USGS) Water-Resources Investigations Report 03-4015 by Sneed and others (2003), describes historical subsidence and groundwater-level changes in the southwest Mojave Desert from 1969 to 1999. The second report, U.S. Geological Survey Water-Resources Investigations Report 07-5097, an online interactive report and map, by Sneed and Brandt (2007), describes subsidence and groundwater-level changes in the southwest Mojave Desert from 1999 to 2004. The purpose of this report is to document an updated assessment of subsidence in these lakebeds and selected neighboring areas from 2004 to 2009 as measured by InSAR methods. In addition, continuous Global Positioning System (GPS)(2005-10), groundwater level (1951-2010), and lithologic data, if available, were used to characterize compaction mechanisms in these areas. The USGS California Water Science Center’s interactive website for the Mojave River and Morongo groundwater basins was created to centralize information pertaining to land subsidence and water levels and to allow readers to access available data and related reports online. An interactive map of land subsidence and water levels in the Mojave River and Morongo groundwater basins displays InSAR interferograms, subsidence areas, subsidence contours, hydrographs, well information, and water-level contours. Background information, including a basic description of the mechanics of land subsidence and InSAR, as well as a description of the study area, is presented within the Mojave Water Resources Interactive Map and report.

California↗
USGS2014

Land subsidence, groundwater levels, and geology in the Coachella Valley, California, 1993-2010

Land subsidence associated with groundwater-level declines has been investigated by the U.S. Geological Survey in the Coachella Valley, California, since 1996. Groundwater has been a major source of agricultural, municipal, and domestic supply in the valley since the early 1920s. Pumping of groundwater resulted in water-level declines as much as 15 meters (50 feet) through the late 1940s. In 1949, the importation of Colorado River water to the southern Coachella Valley began, resulting in a reduction in groundwater pumping and a recovery of water levels during the 1950s through the 1970s. Since the late 1970s, demand for water in the valley has exceeded deliveries of imported surface water, resulting in increased pumping and associated groundwater-level declines and, consequently, an increase in the potential for land subsidence caused by aquifer-system compaction. Global Positioning System (GPS) surveying and Interferometric Synthetic Aperture Radar (InSAR) methods were used to determine the location, extent, and magnitude of the vertical land-surface changes in the southern Coachella Valley during 1993–2010. The GPS measurements taken at 11 geodetic monuments in 1996 and in 2010 in the southern Coachella Valley indicated that the elevation of the land surface changed –136 to –23 millimeters (mm) ±54 mm (–0.45 to –0.08 feet (ft) ±0.18 ft) during the 14-year period. Changes at 6 of the 11 monuments exceeded the maximum expected uncertainty of ±54 mm (±0.18 ft) at the 95-percent confidence level, indicating that subsidence occurred at these monuments between June 1996 and August 2010. GPS measurements taken at 17 geodetic monuments in 2005 and 2010 indicated that the elevation of the land surface changed –256 to +16 mm ±28 mm (–0.84 to +0.05 ft ±0.09 ft) during the 5-year period. Changes at 5 of the 17 monuments exceeded the maximum expected uncertainty of ±28 mm (±0.09 ft) at the 95-percent confidence level, indicating that subsidence occurred at these monuments between August 2005 and August 2010. At each of these five monuments, subsidence rates were about the same between 2005 and 2010 as between 2000 and 2005. InSAR measurements taken between June 27, 1995, and September 19, 2010, indicated that the land surface subsided from about 220 to 600 mm (0.72 to 1.97 ft) in three areas of the Coachella Valley: near Palm Desert, Indian Wells, and La Quinta. In Palm Desert, the average subsidence rates increased from about 39 millimeters per year (mm/yr), or 0.13 foot per year (ft/yr), during 1995–2000 to about 45 mm/yr (0.15 ft/yr) during 2003–10. In Indian Wells, average subsidence rates for two subsidence maxima were fairly steady at about 34 and 26 mm/yr (0.11 and 0.09 ft/yr) during both periods; for the third maxima, average subsidence rates increased from about 14 to 19 mm/yr (0.05 to 0.06 ft/yr) from the first to the second period. In La Quinta, average subsidence rates for five selected locations ranged from about 17 to 37 mm/yr (0.06 to 0.12 ft/yr) during 1995–2000; three of the locations had similar rates during 2003–mid-2009, while the other two locations had increased subsidence rates. Decreased subsidence rates were calculated throughout the La Quinta subsidence area during mid-2009–10, however, and uplift was observed during 2010 near the southern extent of this area. Water-level measurements taken at wells near the subsiding monuments and in the three subsiding areas shown by InSAR generally indicated that the water levels fluctuated seasonally and declined annually from the early 1990s, or earlier, to 2010; some water levels in 2010 were at the lowest levels in their recorded histories. An exception to annually declining water levels in and near subsiding areas was observed beginning in mid-2009 in the La Quinta subsidence area, where recovering water levels coincided with increased recharge operations at the Thomas E. Levy Recharge Facility; decreased pumpage also could cause groundwater levels to recover. Subsidence concomitant with declining water levels and land-surface uplift concomitant with recovering water levels indicate that aquifer-system compaction could be causing subsidence. If the stresses imposed by the historically lowest water levels exceeded the preconsolidation stress, the aquifer-system compaction and associated land subsidence could be permanent.

California↗
USGS2013

Analysis and simulation of regional subsidence accompanying groundwater abstraction and compaction of susceptible aquifer systems in the USA

Regional aquifer-system compaction and land subsidence accompanying groundwater abstraction in susceptible aquifer systems in the USA is a challenge for managing groundwater resources and mitigating associated hazards. Developments in the assessment of regional subsidence provide more information to constrain analyses and simulation of aquifer-system compaction. Current popular approaches to simulating vertical aquifer-system deformation (compaction), such as those embodied in the aquitard drainage model and the MODFLOW subsidence packages, have proven useful from the perspective of regional groundwater resources assessment. However, these approaches inadequately address related local-scale hazards-ground ruptures and damages to engineered structures on the land surface arising from tensional stresses and strains accompanying groundwater abstraction. This paper presents a brief overview of the general approaches taken by the U.S. Geological Survey toward understanding aquifer-system compaction and subsidence with regard to a) identifying the affected aquifer systems; b) making regional assessments; c) analyzing the governing processes; and d) simulating historical and future groundwater flow and subsidence conditions. Limitations and shortcomings of these approaches, as well as future challenges also are discussed.

Boletín de la Sociedad Geológica Mexicana↗
USGS2013

Land subsidence along the Delta-Mendota Canal in the northern part of the San Joaquin Valley, California, 2003-10

Extensive groundwater withdrawal from the unconsolidated deposits in the San Joaquin Valley caused widespread aquifer-system compaction and resultant land subsidence from 1926 to 1970—locally exceeding 8.5 meters. The importation of surface water beginning in the early 1950s through the Delta-Mendota Canal and in the early 1970s through the California Aqueduct resulted in decreased pumping, initiation of water-level recovery, and a reduced rate of compaction in some areas of the San Joaquin Valley. However, drought conditions during 1976–77 and 1987–92, and drought conditions and regulatory reductions in surface-water deliveries during 2007–10, decreased surface-water availability, causing pumping to increase, water levels to decline, and renewed compaction. Land subsidence from this compaction has reduced freeboard and flow capacity of the Delta-Mendota Canal, the California Aqueduct, and other canals that deliver irrigation water and transport floodwater. The U.S. Geological Survey, in cooperation with the U.S. Bureau of Reclamation and the San Luis and Delta-Mendota Water Authority, assessed land subsidence in the vicinity of the Delta-Mendota Canal as part of an effort to minimize future subsidence-related damages to the canal. The location, magnitude, and stress regime of land-surface deformation during 2003–10 were determined by using extensometer, Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), spirit leveling, and groundwater-level data. Comparison of continuous GPS, shallow extensometer, and groundwater-level data, combined with results from a one-dimensional model, indicated the vast majority of the compaction took place beneath the Corcoran Clay, the primary regional confining unit. Land-surface deformation measurements indicated that much of the northern portion of the Delta-Mendota Canal (Clifton Court Forebay to Check 14) was fairly stable or minimally subsiding on an annual basis; some areas showed seasonal periods of subsidence and of uplift that resulted in little or no longer-term elevation loss. Many groundwater levels in this northern area did not reach historical lows during 2003–10, indicating that deformation in this region was primarily elastic. Although the northern portion of the Delta-Mendota Canal was relatively stable, land-surface deformation measurements indicated the southern portion of the Delta-Mendota Canal (Checks 15–21) subsided as part of a large subsidence feature centered about 15 kilometers northeast of the Delta-Mendota Canal, south of the town of El Nido. Results of InSAR analysis indicated at least 540 millimeters of subsidence near the San Joaquin River and the Eastside Bypass during 2008–10, which is part of a 3,200 square-kilometer area—including the southern part of the Delta-Mendota Canal—affected by 20 millimeters or more of subsidence during the same period. Calculations indicated that the subsidence rate doubled in 2008 in some areas. The GPS surveys done in 2008 and 2010 confirmed the high subsidence rate measured by using InSAR for the same period. Water levels in many shallow and deep wells in this area declined during 2007–10; water levels in many deep wells reached historical lows, indicating that subsidence measured during this period was largely inelastic. InSAR-derived subsidence maps for various periods during 2003–10 showed that the area of maximum active subsidence (that is, the largest rates of subsidence) shifted from its historical (1926–70) location southwest of Mendota to south of El Nido. Continued groundwater-level and land-subsidence monitoring in the San Joaquin Valley is important because (1) regulatory- and drought-related reductions in surface-water deliveries since 1976 have resulted in increased groundwater pumping and associated land subsidence, and (2) land use and associated groundwater pumping continue to change throughout the valley. The availability of surface water remains uncertain; even during record-setting precipitation years, such as 2010–11, water deliveries have fallen short of requests and groundwater pumping was required to meet the irrigation demand. Due to the expected continued demand for irrigation supply water and the limitations and uncertainty of surface-water supplies, groundwater pumping and associated land subsidence is likely to continue in the future. Spatially detailed information on land subsidence is needed to facilitate minimization of future subsidence-related damages to the Delta-Mendota Canal and other infrastructure in the San Joaquin Valley. The integration of subsidence, deformation, and water-level measurements—particularly continuous measurements—enables the analysis of aquifer-system response to increased groundwater pumping, which in turn, enables identification of the preconsolidation head and calculation of aquifer-system storage properties. This information can be used to improve numerical model simulations of groundwater flow and aquifer-system compaction and allow for consideration of land subsidence in the evaluation of water-resource management alternatives.

California↗
USGS2012

Geohydrology of Big Bear Valley, California: phase 1--geologic framework, recharge, and preliminary assessment of the source and age of groundwater

The Big Bear Valley, located in the San Bernardino Mountains of southern California, has increased in population in recent years. Most of the water supply for the area is pumped from the alluvial deposits that form the Big Bear Valley groundwater basin. This study was conducted to better understand the thickness and structure of the groundwater basin in order to estimate the quantity and distribution of natural recharge to Big Bear Valley. A gravity survey was used to estimate the thickness of the alluvial deposits that form the Big Bear Valley groundwater basin. This determined that the alluvial deposits reach a maximum thickness of 1,500 to 2,000 feet beneath the center of Big Bear Lake and the area between Big Bear and Baldwin Lakes, and decrease to less than 500 feet thick beneath the eastern end of Big Bear Lake. Interferometric Synthetic Aperture Radar (InSAR) was used to measure pumping-induced land subsidence and to locate structures, such as faults, that could affect groundwater movement. The measurements indicated small amounts of land deformation (uplift and subsidence) in the area between Big Bear Lake and Baldwin Lake, the area near the city of Big Bear Lake, and the area near Sugarloaf, California. Both the gravity and InSAR measurements indicated the possible presence of subsurface faults in subbasins between Big Bear and Baldwin Lakes, but additional data are required for confirmation. The distribution and quantity of groundwater recharge in the area were evaluated by using a regional water-balance model (Basin Characterization Model, or BCM) and a daily rainfall-runoff model (INFILv3). The BCM calculated spatially distributed potential recharge in the study area of approximately 12,700 acre-feet per year (acre-ft/yr) of potential in-place recharge and 30,800 acre-ft/yr of potential runoff. Using the assumption that only 10 percent of the runoff becomes recharge, this approach indicated there is approximately 15,800 acre-ft/yr of total recharge in Big Bear Valley. The INFILv3 model was modified for this study to include a perched zone beneath the root zone to better simulate lateral seepage and recharge in the shallow subsurface in mountainous terrain. The climate input used in the INFILv3 model was developed by using daily climate data from 84 National Climatic Data Center stations and published Parameter Regression on Independent Slopes Model (PRISM) average monthly precipitation maps to match the drier average monthly precipitation measured in the Baldwin Lake drainage basin. This model resulted in a good representation of localized rain-shadow effects and calibrated well to measured lake volumes at Big Bear and Baldwin Lakes. The simulated average annual recharge was about 5,480 acre-ft/yr in the Big Bear study area, with about 2,800 acre-ft/yr in the Big Bear Lake surface-water drainage basin and about 2,680 acre-ft/yr in the Baldwin Lake surface-water drainage basin. One spring and eight wells were sampled and analyzed for chemical and isotopic data in 2005 and 2006 to determine if isotopic techniques could be used to assess the sources and ages of groundwater in the Big Bear Valley. This approach showed that the predominant source of recharge to the Big Bear Valley is winter precipitation falling on the surrounding mountains. The tritium and uncorrected carbon-14 ages of samples collected from wells for this study indicated that the groundwater basin contains water of different ages, ranging from modern to about 17,200-years old.The results of these investigations provide an understanding of the lateral and vertical extent of the groundwater basin, the spatial distribution of groundwater recharge, the processes responsible for the recharge, and the source and age of groundwater in the groundwater basin. Although the studies do not provide an understanding of the detailed water-bearing properties necessary to determine the groundwater availability of the basin, they do provide a framework for the future development of a groundwater model that would help to improve the understanding of the potential hydrologic effects of water-management alternatives in Big Bear Valley.

California↗
USGS2011

The source, discharge, and chemical characteristics of water from Agua Caliente Spring, Palm Springs, California

Agua Caliente Spring, in downtown Palm Springs, California, has been used for recreation and medicinal therapy for hundreds of years and currently (2008) is the source of hot water for the Spa Resort owned by the Agua Caliente Band of the Cahuilla Indians. The Agua Caliente Spring is located about 1,500 feet east of the eastern front of the San Jacinto Mountains on the southeast-sloping alluvial plain of the Coachella Valley. The objectives of this study were to (1) define the geologic structure associated with the Agua Caliente Spring; (2) define the source(s), and possibly the age(s), of water discharged by the spring; (3) ascertain the seasonal and longer-term variability of the natural discharge, water temperature, and chemical characteristics of the spring water; (4) evaluate whether water-level declines in the regional aquifer will influence the temperature of the spring discharge; and, (5) estimate the quantity of spring water that leaks out of the water-collector tank at the spring orifice.

California↗
USGS2009

Cone penetration test and soil boring at the Bayside Groundwater Project Site in San Lorenzo, Alameda County, California

Aquifer-system deformation associated with ground-water-level changes is being investigated cooperatively by the U.S. Geological Survey (USGS) and the East Bay Municipal Utility District (EBMUD) at the Bayside Groundwater Project (BGP) near the modern San Francisco Bay shore in San Lorenzo, California. As a part of this project, EBMUD has proposed an aquifer storage and recovery (ASR) program to store and recover as much as 3.78x104 m3/d of water. Water will be stored in a 30-m sequence of coarse-grained sediment (the 'Deep Aquifer') underlying the east bay alluvium and the adjacent ground-water basin. Storing and recovering water could cause subsidence and uplift at the ASR site and adjacent areas because the land surface will deform as aquifers and confining units elastically expand and contract with ASR cycles. The Deep Aquifer is overlain by more than 150 m of clayey fine-grained sediments and underlain by comparable units. These sediments are similar to the clayey sediments found in the nearby Santa Clara Valley, where inelastic compaction resulted in about 4.3 m of subsidence near San Jose from 1910 to 1995 due to overdraft of the aquifer. The Deep Aquifer is an important regional resource, and EBMUD is required to demonstrate that ASR activities will not affect nearby ground-water management, salinity levels, or cause permanent land subsidence. Subsidence in the east bay area could induce coastal flooding and create difficulty conveying winter storm runoff from urbanized areas. The objective of the cooperative investigation is to monitor and analyze aquifer-system compaction and expansion, as well as consequent land subsidence and uplift resulting from natural causes and any anthropogenic causes related to ground-water development and ASR activities at the BGP. Therefore, soil properties related to compressibility (and the potential for deformation associated with ground-water-level changes) are of the most concern. To achieve this objective, 3 boreholes were drilled at the BGP for the purpose of monitoring pore-fluid pressure changes and aquifer-system deformation. One 308-m deep borehole contains six piezometers, the other two boreholes are 182 and 299 m deep and contain a dual-stage extensometer. To investigate the physical properties of the sediments, two phases of subsurface exploration were conducted. In the first phase, a USGS drilling crew obtained numerous core samples, 5.8 cm in diameter by 1.5 m long. The samples were extracted between July 28, 2006, and August 5, 2006; nine samples were tested for this study at the USGS soils laboratory in Menlo Park, California. Phase two began on June 22, 2006, when a seismic cone penetration test (SCPT) sounding was made to a depth of 32.3 m. Additional field work was completed May 8, 2007, with a hollow-stem auger boring that took continuous 9.8-cm-diameter samples from the depth interval of 6.1 to 10.7 m to supplement poor recovery from the first phase of sampling. These samples were also tested in the soils laboratory at the USGS.

California↗
USGS2007

Detection and Measurement of Land Subsidence Using Global Positioning System Surveying and Interferometric Synthetic Aperture Radar, Coachella Valley, California, 1996-2005

Land subsidence associated with ground-water-level declines has been investigated by the U.S. Geological Survey in the Coachella Valley, California, since 1996. Ground water has been a major source of agricultural, municipal, and domestic supply in the valley since the early 1920s. Pumping of ground water resulted in water-level declines as large as 15 meters (50 feet) through the late 1940s. In 1949, the importation of Colorado River water to the southern Coachella Valley began, resulting in a reduction in ground-water pumping and a recovery of water levels during the 1950s through the 1970s. Since the late 1970s, demand for water in the valley has exceeded deliveries of imported surface water, resulting in increased pumping and associated ground-water-level declines and, consequently, an increase in the potential for land subsidence caused by aquifer-system compaction. Global Positioning System (GPS) surveying and interferometric synthetic aperture radar (InSAR) methods were used to determine the location, extent, and magnitude of the vertical land-surface changes in the southern Coachella Valley. GPS measurements made at 13 geodetic monuments in 1996 and in 2005 in the southern Coachella Valley indicate that the elevation of the land surface had a net decline of 333 to 22 millimeters ?58 millimeters (1.1 to 0.07 foot ?0.19 foot) during the 9-year period. Changes at 10 of the 13 monuments exceeded the maximum uncertainty of ?58 millimeters (?0.19 foot) at the 95-percent confidence level, indicating that subsidence occurred at these monuments between June 1996 and August 2005. GPS measurements made at 20 geodetic monuments in 2000 and in 2005 indicate that the elevation of the land surface changed -312 to +25 millimeters ?42 millimeters (-1.0 to +0.08 foot ?0.14 foot) during the 5-year period. Changes at 14 of the 20 monuments exceeded the maximum uncertainty of ?42 millimeters (?0.14 foot) at the 95-percent confidence level, indicating that subsidence occurred at these monuments between August 2000 and August 2005. Eight of the fourteen monuments for which subsidence rates could be compared indicate that subsidence rates increased by as much as a factor of 10 between 2000 and 2005 compared with subsidence rates before 2000. InSAR measurements made between May 7, 2003, and September 25, 2005, indicate that land subsidence, ranging from about 75 to 180 millimeters (0.25 to 0.59 foot), occurred in three areas of the Coachella Valley: near Palm Desert, Indian Wells, and La Quinta; the equivalent subsidence rates range from about 3 to more than 6 mm/month (0.01 to 0.02 ft/month). The subsiding areas near Palm Desert, Indian Wells, and La Quinta were previously identified using InSAR measurements for 1996-2000, which indicated that about 35 to 150 mm (0.11 to 0.49 ft) of subsidence occurred during the four-year period; the equivalent subsidence rates range from about 1 to 3 mm/month (0.003 to 0.01 ft/month). Comparison of the InSAR results indicates that subsidence rates have increased 2 to 4 times since 2000 in these three areas. Water-level measurements made at wells near the subsiding monuments and in the three subsiding areas generally indicated that the water levels fluctuated seasonally and declined annually between 1996 and 2005; some water levels in 2005 were at the lowest levels in their recorded histories. The coincident areas of subsidence and declining water levels suggest that aquifer-system compaction may be causing subsidence. If the stresses imposed by the historically lowest water levels exceeded the preconsolidation stress, the aquifer-system compaction and associated land subsidence may be permanent. Although the localized character of the subsidence signals is typical of the type of subsidence characteristically caused by localized ground-water pumping, the subsidence may also be related to tectonic activity in the valley.

Scientific Investigations Report↗
USGS2006

Water Resources Investigations at Edwards Air Force Base since 1988

Edwards Air Force Base (EAFB) in southern California (fig. 1) has relied on ground water to meet its water-supply needs. The extraction of ground water has led to two major problems that can directly affect the mission of EAFB: declining water levels (more than 120 ft since the 1920s) and land subsidence, a gradual downward movement of the land surface (more than 4 ft since the late 1920s). As water levels decline, this valuable resource becomes depleted, thus requiring mitigating measures. Land subsidence has caused cracked (fissured) runways and accelerated erosion on Rogers lakebed. In 1988, the U.S. Geological Survey (USGS), in cooperation with the U.S. Air Force, began investigations of the effects of declining water levels and land subsidence at EAFB and possible mitigation measures, such as the injection of imported surface water into the ground-water system. The cooperative investigations included data collection and analyses, numerical simulations of ground-water flow and land subsidence, and development of a preliminary simulation-optimization model. The results of these investigations indicate that the injection of imported water may help to control land subsidence; however, the potential ground-water-quality impacts are unknown.

Fact Sheet↗
USGS2003

Water-level changes induced by local and distant earthquakes at Long Valley caldera, California

Distant as well as local earthquakes have induced groundwater-level changes persisting for days to weeks at Long Valley caldera, California. Four wells open to formations as deep as 300 m have responded to 16 earthquakes, and responses to two earthquakes in the 3-km-deep Long Valley Exploratory Well (LVEW) show that these changes are not limited to weathered or unconsolidated near-surface rocks. All five wells exhibit water-level variations in response to earth tides, indicating they can be used as low-resolution strainmeters. Earthquakes induce gradual water-level changes that increase in amplitude for as long as 30 days, then return more slowly to pre-earthquake levels. The gradual water-level changes are always drops at wells LKT, LVEW, and CH-10B, and always rises at well CW-3. At a dilatometer just outside the caldera, earthquake-induced strain responses consist of either a step followed by a contractional strain-rate increase, or a transient contractional signal that reaches a maximum in about seven days and then returns toward the pre-earthquake value. The sizes of the gradual water-level changes generally increase with earthquake magnitude and decrease with hypocentral distance. Local earthquakes in Long Valley produce coseismic water-level steps; otherwise the responses to local earthquakes and distant earthquakes are indistinguishable. In particular, water-level and strain changes in Long Valley following the 1992 M7.3 Landers earthquake, 450 km distant, closely resemble those initiated by a M4.9 local earthquake on November 22, 1997, during a seismic swarm with features indicative of fluid involvement. At the LKT well, many of the response time histories are identical for 20 days after each earthquake, and can be matched by a theoretical solution giving the pore pressure as a function of time due to diffusion of a nearby, instantaneous, pressure drop. Such pressure drops could be produced by accelerated inflation of the resurgent dome by amounts too small to be detected by the two-color electronic distance-measuring network. Opening-mode displacement in the south moat, inferred to have followed a M4.9 earthquake on November 22, 1997, could also create extensional strain on the dome and lead to water-level changes similar to those following dome inflation. Contractional strain that could account for earthquake-induced water-level rises at the CW-3 well is inconsistent with geodetic observations. We instead attribute these water-level rises to diffusion of elevated fluid pressure localized in the south moat thermal aquifer. For hydraulic diffusivities appropriate to the upper few hundred meters at Long Valley, an influx of material at temperatures of 300°C can thermally generate pressure of 6 m of water or more, an order of magnitude larger than needed to account for the CW-3 water-level rises. If magma or hot aqueous fluid rises to within 1 km of the surface in the eastern part of the south moat, then hydraulic diffusivities are high enough to allow fluid pressure to propagate to CW-3 on the time scale observed. The data indicate that seismic waves from large distant earthquakes can stimulate upward movement of fluid in the hydrothermal system at Long Valley.

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USGS2003

The Long Valley Caldera GIS database

This database provides an overview of the studies being conducted by the Long Valley Observatory in eastern California from 1975 to 2001. The database includes geologic, monitoring, and topographic datasets related to Long Valley caldera. The CD-ROM contains a scan of the original geologic map of the Long Valley region by R. Bailey. Real-time data of the current activity of the caldera (including earthquakes, ground deformation and the release of volcanic gas), information about volcanic hazards and the USGS response plan are available online at the Long Valley observatory web page (http://lvo.wr.usgs.gov). If you have any comments or questions about this database, please contact the Scientist in Charge of the Long Valley observatory.

Data Series↗
USGS2003

Measuring human-induced land subsidence from space

Satellite Interferometric Synthetic Aperture Radar (InSAR) is a revolutionary technique that allows scientists to measure and map changes on the Earth's surface as small as a few millimeters. By bouncing radar signals off the ground surface from the same point in space but at different times, the radar satellite can measure the change in distance between the satellite and ground (range change) as the land surface uplifts or subsides. Maps of relative ground-surface change (interferograms) are constructed from the InSAR data to help scientists understand how ground-water pumping, hydrocarbon production, or other human activities cause the land surface to uplift or subside. Interferograms developed by the USGS for study areas in California, Nevada, and Texas are used in this fact sheet to demonstrate some of the applications of InSAR to assess human-induced land deformation

Fact Sheet↗
USGS2003

Earthquakes-Rattling the Earth's Plumbing System

Hydrogeologic responses to earthquakes have been known for decades, and have occurred both close to, and thousands of miles from earthquake epicenters. Water wells have become turbid, dry or begun flowing, discharge of springs and ground water to streams has increased and new springs have formed, and well and surface-water quality have become degraded as a result of earthquakes. Earthquakes affect our Earth’s intricate plumbing system—whether you live near the notoriously active San Andreas Fault in California, or far from active faults in Florida, an earthquake near or far can affect you and the water resources you depend on.

Fact Sheet↗