Geology topics

Linzy K. Foster

Publications and source records attributed to Linzy K. Foster.

7 recordsLinked to original sources

USGS2023

Hydrogeology, land-surface subsidence, and documentation of the Gulf Coast Land Subsidence and Groundwater-Flow (GULF) model, southeast Texas, 1897–2018

Executive Summary As a part of the Texas Water Development Board groundwater availability modeling program, the U.S. Geological Survey developed the Gulf Coast Land Subsidence and Groundwater-Flow model (hereinafter, the “GULF model”) and ensemble to simulate groundwater flow and land-surface subsidence in the northern part of the Gulf Coast aquifer system (the study area) in Texas from predevelopment (1897) through 2018. Since the publication of a previous groundwater model for the greater Houston area in 2012, there have been changes to the distribution of groundwater withdrawals and advances in modeling tools. To reflect these changes and to simulate more recent conditions, the GULF model was developed in cooperation with the Harris-Galveston and Fort Bend Subsidence Districts to provide an updated Groundwater Availability Model. Since the early 1900s, most of the groundwater withdrawals in the study area have been from three of the hydrogeologic units that compose the Gulf Coast aquifer system—the Chicot, Evangeline, and Jasper aquifers and, more recently, from the Catahoula confining unit. Withdrawals from these hydrogeologic units are used for municipal supply, commercial and industrial use, and irrigation purposes. Withdrawals of large quantities of groundwater in the greater Houston area have caused widespread groundwater-level declines in the Chicot, Evangeline, and Jasper aquifers of more than 300 feet (ft). Early development of the aquifer system, which began before 1900, resulted in nearly 50 percent of the eventual historical groundwater-level minimums having been reached as early as 1946 in some areas. These groundwater-level declines led to more than 9 ft of land-surface subsidence—historically in central and southeastern Harris County and Galveston County, but more recently in northern, northwestern, and western Harris County, Montgomery County, and northern Fort Bend County—from depressurization and compaction of clay and silt layers interbedded in the aquifer sediments. In a generalized conceptual model of the Gulf Coast aquifer system, water enters the groundwater system in topographically high outcrops of the hydrogeologic units in the northwestern part of the aquifer system. Groundwater that does not discharge to streams flows to intermediate and deep zones of the aquifer system southeastward of the outcrop areas where it is discharged by wells and by upward leakage in topographically low areas near the coast. The uppermost parts of the aquifer system, which include outcrop areas, are under water-table (unconfined) conditions where the groundwater is not confined under pressure. As depth increases in the aquifer system and interbedded clay and silt layers accumulate, water-table conditions evolve into confined conditions where the groundwater is under pressure. Groundwater flow and land-surface subsidence in the GULF model and ensemble were simulated by using MODFLOW 6 with the Skeletal Storage, Compaction, and Subsidence package. The model consists of six layers, one for each of the five hydrogeologic units in the northern part of the Gulf Coast aquifer system and a surficial top layer that includes part of each hydrogeologic unit. Transient groundwater flow was simulated during 1897–2018 by using a combination of multiyear, annual, and monthly stress periods. An initial steady-state stress period was configured to represent predevelopment mean annual inflows and outflows. The subsidence package used in the GULF model and ensemble uses a head-based subsidence formulation that simulates the delayed drainage response from clay and silt sediment to changes in groundwater levels. The GULF model and ensemble were history matched to groundwater-level observations at selected wells, land-surface subsidence at benchmarks, aquifer compaction at borehole extensometers, and vertical displacement from Global Positioning System stations. A Bayesian framework was used to represent uncertainty in modeled parameters and simulated outputs of interest. History matching and uncertainty quantification were performed by using a Monte Carlo approach enabled through iterative ensemble smoother software to produce an ensemble of models fit to historical data. The iterative ensemble smoother substantially reduced the computational demand of parameter estimation by approximating the first-order relation between model inputs and outputs, thereby allowing 183,207 adjustable parameters to be used for history matching at a relatively low computational and time cost. The history-matched parameter values are within the ranges of previously published values and agree with the current understanding of the spatial and temporal patterns of parameter uncertainty for the Gulf Coast aquifer system. A good agreement between the observed (or estimated) and simulated groundwater levels, land-surface subsidence, compaction, and vertical displacement was obtained across the modeled area based on qualitative and quantitative comparisons. Ensemble mean annual groundwater-flow rates to the Chicot, Evangeline, Jasper aquifers and Catahoula confining unit were 0.0–0.49 inch (in.), 0.09–0.33 in., 0.01–0.07 in., and 0.01–0.05 in., respectively. GULF model mean annual groundwater-flow rates to the Chicot, Evangeline, and Jasper aquifers and Catahoula confining unit were 0.31 in., 0.19 in., 0.03 in., and 0.03 in., respectively. The GULF-model-simulated recharge to the outcrop area was the largest inflow (75 percent), and recharge to other areas was 25 percent of the model inflow. The simulated outflows included (1) net surface-water/groundwater exchange with study area streams (50 percent), (2) groundwater use (49 percent), and (3) net surface-water/groundwater exchange with the Gulf of Mexico (1 percent). The sum of the simulated values of the outflows (1,041,973 acre-feet per year [acre-ft/yr]) and the elastic expansion of the fine-grained sediment and numerical solver error (339 acre-ft/yr) minus the inflows (654,172 acre-ft/yr) represents the reduction of storage from the Gulf Coast aquifer system (388,140 acre-ft/yr). Most of the storage depletion is caused by the long-term groundwater-level declines that have resulted primarily in inelastic compaction. The GULF model was used to estimate Jasper aquifer compaction at selected benchmarks in Montgomery County and northern Harris County, which are the primary locations of Jasper aquifer groundwater use. Simulated Jasper aquifer compaction in northern Harris County was between 0.2 and 0.5 ft, or between about 5 and 16 percent of simulated subsidence at the benchmark locations. Simulated Jasper aquifer compaction in Montgomery County was between 0.8 and 1.2 ft, or between about 33 and 57 percent of simulated subsidence at the benchmark locations.

Texas↗

USGS2022

Upper Rio Grande Basin water-resource status and trends: Focus area study review and synthesis

The Upper Rio Grande Basin (URGB) is a critical international water resource under pressure from a myriad of climatic, ecological, infrastructural, water-use, and legal constraints. The objective of this study is to provide a comprehensive assessment of the spatial distribution and temporal trends of selected water-budget components (snow processes, evapotranspiration (ET), streamflow processes, and groundwater storage) using integrated analyses, such as watershed modeling and water availability and use data in the URGB over the past three decades. A spatially distributed snow evolution modeling system simulated snowpack processes over 34 years (1984–2017). It highlighted snow water equivalent declines from -35 to -77 mm/decade with widespread variability across elevation zones and land cover types. Gridded actual ET data from the SSEBop model were developed and tested for the URGB and demonstrated that all land-cover types had significant decreasing trends (1986-2015) ranging from -14 to -80 mm/decade. Conductivity-mass-balance (CMB) hydrograph separation results found that baseflow forms a large component of total streamflow, ranging from 29 to 69% (49% average) of total streamflow at 17 URGB sites upstream of Albuquerque, NM. Three of 4 graphical hydrograph separation methods in the U.S. Geological Survey Groundwater Toolbox were found to be inappropriate for estimating baseflow in the URGB; the most promising method, baseflow index (BFI) Standard, was optimized using CMB data and tested at three URGB sites, with resulting overestimation of 0 to 47%. Simulated changes in groundwater storage were extracted from historical and recent groundwater-flow models of select alluvial basins (San Luis, Española, Middle Rio Grande, and Tularosa-Hueco). In general, decreases in groundwater storage were observed from 1903 to 2013 except for the San Luis alluvial basin (Colorado), where periods of recovery are observed. The PRMS hydrologic model was successfully calibrated for 9 near-native subbasins (Nash-Sutcliffe efficiency 0.47 to 0.85) and parameters translated to the remaining subbasins; compared to simulated near-native flows (with minimal influence of reservoirs or diversions), observed Rio Grande streamgage flows demonstrated reductions of 40% or more for New Mexico and Texas areas of the basin. Significant decreasing trends (1980-2015) in precipitation, snowmelt rate, streamflow, and baseflow were observed at many of the 12 streamgage basins studied, which suggests that the decreasing trends for actual ET may be related to overall decreasing water availability in the basin, with negative implications for agricultural production and groundwater abstraction. Water security concerns arise from our findings of higher fraction precipitation as rain, slower snowmelt rates leading to decreasing streamflow production, and an increasing fraction of baseflow, all of which will affect the timing and magnitude of water available for human needs in the basin.

Upper Rio Grande Basin↗

USGS2021

Hydrogeologic framework and groundwater characterization in selected alluvial basins in the upper Rio Grande basin, Colorado, New Mexico, and Texas, United States, and Chihuahua, Mexico, 1980 to 2015

Increasing demand for the limited water resources of the United States continues to put pressure on resource management agencies to balance the competing needs of ecosystem health with municipal, agricultural, and other uses. To meet these needs, the U.S. Geological Survey conducted a multiyear study to evaluate water resources in the upper Rio Grande Basin in the southwestern United States. The upper Rio Grande Basin extends from south-central Colorado, through New Mexico, into west Texas near Fort Quitman, including parts of Chihuahua, Mexico. The upper Rio Grande Basin consists of a sequence of alluvial basins that formed in the Rio Grande rift approximately 30 million years ago. This report describes the hydrogeology of the upper Rio Grande Basin and how the groundwater resources in the basin have changed from 1980 to 2015. The hydrogeologic framework includes the horizontal delineation of the alluvial basins within the upper Rio Grande Basin from the headwaters in Colorado to Fort Quitman, Texas, including part of Mexico. Groundwater-level measurements from existing State and Federal data were used to construct groundwater-level altitude and groundwater-level change maps. Of the 2,699 wells with groundwater-level data used in this study, 1,055 wells had data for only a single 5-year period, 703 wells had data for 50 percent or more of the 35 years of the study, and only 57 wells have 5-year groundwater-level data for the entire study period. The median decline in water levels in the upper Rio Grande Basin was 0.13 foot (ft) per 5-year period, and declines were measured in 53 percent of the 703 wells that contained data for 50 percent or more of the study period. Rates of groundwater-level decline greater than 1 ft per 5-year period were measured in 17 percent of the wells, greater than 2 ft per 5-year period, in 3 percent of the wells, and greater than 3 ft per 5-year period, in 1 percent of the wells. Overall, groundwater levels rose in 6 percent of the 703 wells that contained data for 50 percent or more of the study period, and in 4 percent of the wells, groundwater levels rose by 1 ft or more per 5-year period. Groundwater-level changes in wells with consecutive 5-year measurement periods exhibited the most variability in the Española, Middle Rio Grande, and Mesilla/Conejos-Médanos alluvial basins. The largest declines in groundwater-level altitudes in individual wells were observed in the Española alluvial basin during 1995–2000, in the Palomas alluvial basin during 2010–2015, and in the Jornada del Muerto alluvial basin during 2005–10. The largest rises in groundwater-level altitudes in individual wells were observed in the Española alluvial basin during 2005–10, in the Middle Rio Grande alluvial basin during 1995–2000, and in the Mesilla/Conejos-Médanos alluvial basin during 1980–85. Changes in groundwater storage throughout the study period varied by alluvial basin, likely based largely on changes in groundwater withdrawals because of increased demands during drier periods and population growth. All alluvial basins except the Tularosa-Hueco alluvial basin were evaluated for changes in groundwater storage from 1980 to 2015. Extremely limited data availability in 2010–15 for the Tularosa-Hueco alluvial basin led to this 5-year period being dropped from the groundwater-level change map and storage analysis for this basin. In the San Luis Valley in southern Colorado, efforts to reverse groundwater depletion in the unconfined aquifer recovered approximately 250,000 acre-feet in storage between late 2013 and early 2018, following the implementation of a “pay-to-pump” groundwater program. However, severe drought that persists in the upper Rio Grande Basin, particularly in southern Colorado, has undone some of the conservation efforts. Within the Española alluvial basin, groundwater storage varied because municipal demand increased the demand on groundwater resources and conservation efforts were implemented. A groundwater-flow model evaluated for the Española alluvial basin indicated declines in groundwater storage from 1947 through 1982. Groundwater storage decreased in the Española alluvial basin in 1980–85, 1985–90, 1990–95, 1995–2000, and 2005–10 and increased in 2000–05 and 2010–15 leading to groundwater storage in 2015 about even with that in 1985. Based on gridded groundwater-level altitudes, groundwater storage decreased in the Middle Rio Grande Basin from 1980 to 2015, except for during the 1980–85, 2000–05, and 2010–15 periods with an overall cumulative storage decrease from 1980 to 2015. Groundwater-flow models evaluated for the Middle Rio Grande alluvial basin showed groundwater storage in the Middle Rio Grande alluvial basin has been reduced since the mid-1950s through the end of the study period except for a brief recovery (reduction in storage outflow) in the mid-1980s. Simulated groundwater storage has also decreased in parts of the Palomas and Mesilla/Conejos-Médanos alluvial basins, and the northern part of the Conejos-Médanos alluvial basin starting in 1995 (excluding 2005 and 2007) and in the Tularosa-Hueco alluvial basin from the early 1940s to the end of the study period. Groundwater storage increased in the Mesilla/Conejos-Médanos alluvial basin during 1980–85 and slightly during 1990–95 and then decreased in the other 5-year periods. Groundwater storage in the Tularosa-Hueco alluvial basin increased from 1985 to 1990, but otherwise decreased, leading to an overall net groundwater-level decline in this part of the basin from 1980 to 2010.

Colorado, New Mexico, Texas, Chihuahua↗

USGS2021

Risk-based decision-support groundwater modeling for the lower San Antonio River Basin, Texas, USA

A numerical surface-water/groundwater model was developed for the lower San Antonio River Basin to evaluate the responses of low base flows and groundwater levels within the basin under conditions of reduced recharge and increased groundwater withdrawals. Batch data assimilation through history matching used a simulation of historical conditions (2006-2013); this process included history-matching to groundwater levels and base-flow estimates at several gages, and was completed in a high-dimensional (highly parameterized) framework. The model was developed in an uncertainty framework such that parameters, observations, and scenarios of interest are envisioned stochastically as distributions of potential values. Results indicate that groundwater contributions to surface water during periods of low flow may be reduced from 6% to 25% with a corresponding 25% reduction in recharge and a 25% increase in groundwater pumping over an 8-year planning period. Furthermore, results indicate groundwater-level reductions in some hydrostratigraphic units are more likely than in other hydrostratigraphic units over an 8-year period under drought conditions with the higher groundwater withdrawal scenario.

Texas↗

USGS2021

Extending the capture map concept to estimate discrete and risk-based streamflow depletion potential

A popular and contemporary use of numerical groundwater models is to estimate the discrete relation between groundwater extraction and surface-water/groundwater exchange. Previously, the concept of a “capture map” has been put forward as a means to effectively summarize this relation for decision-making consumption. While capture maps have enjoyed success in the environmental simulation industry, they are deterministic, ignoring uncertainty in the underlying model. Furthermore, capture maps are not typically calculated in a manner that facilitates analysis of varying combinations of extraction locations and/or reaches. That is, they are typically constructed with focus on a single reach or group of reaches. The former of these limitations is important for conveying risk to decision makers and stakeholders, while the latter is important for decision-making support related to surface-water management, where future foci may include reaches that were not the focus of the original capture analysis. Herein, we use the concept of a response matrix to generalize the theory of the capture-map approach to estimate spatially discrete streamflow depletion potential. We also use first-order, second-moment uncertainty estimation techniques with the concept of “risk shifting” to place capture maps and streamflow depletion potential in a stochastic, risk-based framework. Our approach is demonstrated for an integrated groundwater/surface-water model of the lower San Antonio River, Texas, USA.

Groundwater↗

USGS2020

Towards reproducible environmental modeling for decision support: A worked example

A fully worked example of decision-support-scale uncertainty quantification (UQ) and parameter estimation (PE) is presented. The analyses are implemented for an existing groundwater flow model of the Edwards aquifer, Texas, USA, and are completed in a script-based workflow that strives to be transparent and reproducible. High-dimensional PE is used to history-match simulated outputs to corresponding state observations of spring flow and groundwater level. Then a hindcast of a historical drought is made. Using available state observations recorded during drought conditions, the combined UQ and PE analyses are shown to yield an ensemble of model results that bracket the observed hydrologic responses. All files and scripts used for the analyses are placed in the public domain to serve as a template for other practitioners who are interested in undertaking these types of analyses.

Texas↗

USGS2016

New insights into the Edwards Aquifer—Brackish-water simulation, drought, and the role of uncertainty analysis

The Edwards aquifer is an important water resource in south-central Texas, providing water for residents, businesses, and ecosystems. The aquifer is a highly complex karst system characterized by areas of rapid groundwater flow, faulted and fractured Cretaceous-age rocks, and multiple water-quality zones. Karst aquifer systems include soluble rocks such as limestone and dolomite that can convey tremendous amounts of water through dissolution-enhanced faults and fractures. Recent sustained droughts (2011–15) have heightened concerns about the possible effects of drought on this vital water resource. The Edwards aquifer consists of three water-quality zones. The freshwater zone of the Edwards aquifer is bounded to the south by a zone of brackish water (transition zone) where the aquifer transitions from fresh to saline water. The saline zone is downdip from the transition zone. There is concern that a recurrence of extreme drought, such as the 7-year drought from 1950 through 1956, could cause the transition zone to move toward (encroach upon) the freshwater zone, causing production wells near the transition zone to pump saltier water. There is also concern of drought effects on spring flows from Comal and San Marcos Springs. These concerns were evaluated through the development of a new numerical model of the Edwards aquifer.

Texas↗