Browsing by Subject "Hydrogeology"
Now showing 1 - 17 of 17
Results Per Page
Sort Options
Item Constraining fracture permeability by characterizing fracture surface roughness(2010-12) Al-Johar, Mishal Mansour; Sharp, John Malcolm, 1944-; Ketcham, Richard A.; Cardenas, Meinhard B.Open and connected fractures, where present, control fluid flow and dominate solute transport. Flow through fractures has major implications for water resource management, underground waste repositories, contaminant remediation, and hydrocarbon exploitation. Complex fracture morphology makes it difficult to quantify and predict flow and transport accurately. The difficulty in usefully describing the complex morphology of a real fracture from a small 3-D volume or 2-D profile sample remains unresolved. Furthermore, even when complex fracture morphology is measured across three-dimensions, accurate prediction of discharge remains difficult. High resolution x-ray computed tomography (HXRCT) data collected for over 20 rock surfaces and fractures provide a useful dataset to study fracture morphology across scales of several orders of magnitude. Samples include fractured rock of varying lithology, including sandstone, volcanic tuffs and crystalline igneous and metamorphic rocks. Results suggest that the influence of grain size on surface roughness is not readily apparent due to other competing variables such as mechanics, skins and coatings, and weathering and erosion. Flow tests of HXRCT-scanned fractures provide real discharge data allowing the hydraulic aperture to be directly measured. Scale-invariant descriptions of surface roughness can produce constrained estimates of aperture variability and possibly yield better predictions of fluid flow through fractures. Often, a distinction is not made between the apparent and true fracture apertures for rough fractures measured on a 2-D topographic grid. I compare a variety of local aperture measurements, including the apparent aperture, two-dimensional circular tangential aperture, and three-dimensional spherical tangential aperture. The mechanical aperture, the arithmetic mean of the apparent local aperture, is always the largest aperture. The other aperture metrics vary in their ranking, but remain similar. Results suggest that it may not be necessary to differentiate between the apparent and true apertures. Rock fracture aperture is the predominant control on permeability, and surface roughness controls fracture aperture. A variety of surface roughness characterizations using statistical and fractal methods are compared. A combination of the root-mean-square roughness and the surface-to-footprint ratio are found to be the most useful descriptors of rock fracture roughness. Mated fracture surfaces are observed to have nearly identical characterizations of fracture surface roughness, suggesting that rock fractures can be sampled by using only one surface, resulting in a significantly easier sampling requirement. For mated fractures that have at least one point in contact, a maximum potential aperture can be constrained by reflecting and translating a single surface. The maximized aperture has a nearly perfect correlation with the RMS roughness of the surface. These results may allow better predictions of fracture permeability thereby providing a better understanding of subsurface fracture flow for applications to contaminant remediation and water and hydrocarbon management. Further research must address upscaling fracture morphology from hand samples to outcrops and characterizing entire fracture networks from samples of single fractures.Item Evaluation of Collector Well Configurations to Model Hydrodynamics in Riverbank Filtration and Groundwater Remediation(2011-10-21) De Leon, Tiffany LucindaCollector well designs are necessary to maximize groundwater uptake and riverbank filtration without negatively impacting an aquifer. Unfortunately, there is a lack of information and research regarding the implementation of collector well design parameters. In the past, collector well installation was too costly, but recent advances in well technology have made collector wells more cost effective. This research will contribute a set of guidelines to optimize riverbank filtration and groundwater remediation. This study models the hydrodynamics surrounding collector well configurations in riverbank filtration and groundwater remediation. Visual Modflow? was utilized to run a variety of numerical models to test four areas: flux along the laterals of a collector well, collector well interactions with a river, collector well yield, and collector well remediation capability. The two design parameters investigated were lateral length (25 m, 50 m, and 100 m) and number of laterals (3 and 4). The lateral flux tests confirm flux increases towards the terminal end of each lateral and pumping rate is the controlling factor in flux amount obtained along the laterals. The analysis of the flux-river interaction shows the main factor in determining flux amount is the initial river geometry, followed by the pumping rate, regional background flow, and collector well design, respectively. The models suggest that the 4-lateral collector well design is more effective than the 3-lateral design and in addition, 100 meter length laterals provide the highest amount of yield with the least amount of drawdown. The remediation tests investigate the application of vertical well equations to evaluate collector well designs in two areas: minimum pumping rate to capture line source of particles and first arrival time of particles. The remediation models show 100 meter length laterals provide both the lowest pumping rate and the highest residence time with the surrounding aquifer for maximum remediation. Ultimately, these models provide basic design guidelines and explain which designs are most effective, depending on the collector well purpose.Item An experimental assessment of the influence of bedforms on coupled hyporheic flow and heat transport(2013-05) Norman, Francis Alexander, IV; Cardenas, Meinhard Bayani, 1977-Hyporheic flow influences both biogeochemical cycling in streambeds as well as streambed ecology. Some biogeochemical processes may be temperature dependent; therefore, heat transport associated with hyporheic flow may be an important influence on such cycles. I separately and experimentally assessed the effects of hyporheic flow due to bed topography on thermal dynamics in the sediment using a custom, tilting flume with temperature controls. Diel temperature cycles of 6° C were imposed in the flume and propagation of temperature signals into the sediment was examined for different bed morphologies (plane bed, pool-riffle-pool, and rippled bed), channel flow rates, and sediment grain sizes. Temperature fields in the sediment were monitored using an array of embedded thermistors, and this data was used to identify zones of upwelling and downwelling within the hyporheic zone. Results suggest that bedforms do induce substantially deeper downwelling upstream and downstream of the bedforms, with upwelling near the crest. This in turn leads to substantial advective heat transport and distinct thermal patterns in the sediment. Variation in permeability and channel flow rates further affects the magnitude of this advective transport. These results corroborate existing theoretical models of coupled hyporheic exchange and heat transport under bedforms. Hyporheic flow therefore affects thermal patchiness in sediment, which may in turn exert a control on biogeochemical reaction rates, and form thermal refugia for fauna.Item Experimental measurements of condensate blocking and treatements in low and high permeability cores(2003) Al-Anazi, Hamoud Ali; Sharma, Mukul M.; Pope, G. A.Experiments were performed to investigate the effect of condensate and water blocking on gas productivity in both low and high permeability cores. Liquid dropout data for a four-component synthetic gas mixture was measured experimentally. The Peng-Robinson equation-of-state was used to calculate the liquid drop and matched the data closely after a small adjustment in the gas composition. Coreflood experiments were conducted to measure relative permeability using Berea sandstone and Texas Cream limestone cores and the four-component synthetic gas mixture to quantify the loss in relative permeability caused by condensate blocking. The condensate saturation was established dynamically by precise control of core inlet and outlet pressures. It is well known that retrograde condensate blockage can cause significant productivity loss in low permeability gas reservoirs. This research shows that such productivity losses can also occur in high permeability gas reservoirs. Gas relative permeability reductions of up to 97% were measured in 3 md and 350 md cores during steady state flow of gas and condensate (see Table 5.1). Higher initial water saturations resulted in higher reductions in gas relative permeability. Gas and condensate relative permeability values are almost equal at steady state flow of gas and condensate. Values as low as 0.04 were measured at the highest initial water saturation. Methanol treatments in the same cores increased both gas and condensate relative permeability in both low and high permeability rocks. These coreflood experiments also were used to quantify the methanol treatment volumes required to restore the gas relative permeability. Methanol displaces condensate and maintains improved gas relative permeability for a significant period of time after the treatment even with production below the dew point pressure. Methanol miscibility displaces water, which is also beneficial since water contributes to the total liquid blockage of the gas. These same coreflood experiments showed that dynamic condensate accumulation is influenced by flow rate. More pore volumes were required to reach a steady state at high flow rates than a low flow rates. Co-injection equilibrium gas and condensate phases into the core achieved a steady state with fewer pore volumes than the high flow rate dynamic accumulation corefloods. These data show that local equilibrium was not reached at the high flow rates. At the highest flow rates, the residence time in the core was only about 9 minutes, which evidently is not sufficient time for complete mass transfer to occur. However, it is important to note that the steady state values of gas and condensate relative permeability are the same for both methods. These values will be reached very quickly around gas wells with high flow rate due to the large number of pore volumes flowing near the well. In light of these new data, the common perception that condensate blocking around wells in high-permeability gas reservoirs is not significant should be re-examined. Reservoir engineers should be especially careful to evaluate the damage done in such high-permeability reservoirs if the well's pressure drawdown is high enough to result in pressures below the dew point over a long enough period of time to allow condensate accumulation near the well.Item GPR Method for the Detection and Characterization of Fractures and Karst Features: Polarimetry, Attribute Extraction, Inverse Modeling and Data Mining Techniques(2011-02-22) Sassen, Douglas SpencerThe presence of fractures, joints and karst features within rock strongly influence the hydraulic and mechanical behavior of a rock mass, and there is a strong desire to characterize these features in a noninvasive manner, such as by using ground penetrating radar (GPR). These features can alter the incident waveform and polarization of the GPR signal depending on the aperture, fill and orientation of the features. The GPR methods developed here focus on changes in waveform, polarization or texture that can improve the detection and discrimination of these features within rock bodies. These new methods are utilized to better understand the interaction of an invasive shrub, Juniperus ashei, with subsurface flow conduits at an ecohydrologic experimentation plot situated on the limestone of the Edwards Aquifer, central Texas. First, a coherency algorithm is developed for polarimetric GPR that uses the largest eigenvalue of a scattering matrix in the calculation of coherence. This coherency is sensitive to waveshape and unbiased by the polarization of the GPR antennas, and it shows improvement over scalar coherency in detection of possible conduits in the plot data. Second, a method is described for full-waveform inversion of transmission data to quantitatively determine fracture aperture and electromagnetic properties of the fill, based on a thin-layer model. This inversion method is validated on synthetic data, and the results from field data at the experimentation plot show consistency with the reflection data. Finally, growing hierarchical self-organizing maps (GHSOM) are applied to the GPR data to discover new patterns indicative of subsurface features, without representative examples. The GHSOMs are able to distinguish patterns indicating soil filled cavities within the limestone. Using these methods, locations of soil filled cavities and the dominant flow conduits were indentified. This information helps to reconcile previous hydrologic experiments conducted at the site. Additionally, the GPR and hydrologic experiments suggests that Juniperus ashei significantly impacts infiltration by redirecting flow towards its roots occupying conduits and soil bodies within the rock. This research demonstrates that GPR provides a noninvasive tool that can improve future subsurface experimentation.Item Groundwater flow and recharge within the Barton Springs segment of the Edwards Aquifer, southern Travis and northern Hays Counties, Texas(2009-05) Hauwert, Nico Mark; Sharp, John Malcolm, 1944-The Barton Springs Segment, part of the karstic Edwards aquifer in Central Texas, is a Sole Source aquifer, is habitat to rare karst species, and provides water to a well-loved municipal swimming pool, yet its hydrogeologic properties remain insufficiently understood. For this study, the hydrogeologic characteristics of the Barton Springs Segment were investigated using several approaches, including mapping of hydrostratigraphic units and faults, measurement of upland infiltration, groundwater traces, and aquifer tests. The depositional environment, diagenesis, fracturing, down-dropped and dipping faulted blocks, and subsequent dissolution were determined to play important roles in controlling groundwater flow-path development within the Barton Springs Segment. In particular, downdropped fault blocks create groundwater gradients to the southeast that influence flow in the Edwards outcrop area. Upland internal drainage basins were found to be extremely efficient at conveying recharge to the underlying aquifer. The maturity of natural internal drainage sinkholes can be measured by its bowl volume, which grows in proportion to the catchment area it captures. A 19-hectare internal drainage basin, HQ Flat sinkhole, was monitored for rainfall, evapotranspiration, soil moisture, and discrete runoff to the cave drain. During a 505-day period, 5.5% of measured rainfall entered the cave drain as discrete recharge, 26% of measured rainfall infiltrated through soils on the slopes, and the remaining 68% was lost through evapotranspiration. This amount of upland infiltration is consistent with infiltration measurements in other karst areas and is much larger than the 1% upland recharge of rainfall that was previously estimated. A chloride mass balance indicates that at the adjacent Tabor research site, about 50% of rainfall infiltrates to a 6-meter depth. Dye-tracing and pump tests demonstrated that primary and secondary groundwater flow paths are the major influence on transmissivity within the Barton Springs Segment. Groundwater tracing breakthroughs reveal very high advection and relatively low dispersion. Drawdown response to pump tests indicates a very high degree of anisotropy, controlled by location of groundwater flow paths. Overall the Barton Springs Segment is a mature karst aquifer with highly developed rapid, discrete network for both recharge and groundwater-flow.Item Hydrogeochemistry of the unsaturated zone of a salt flat in Hudspeth County, Texas(1984-12) Chapman, Jeannette Elise Burgen; Kreitler, Charles W.The playas of the Salt Basin in Trans-Pecos Texas are natural laboratories for the study of the hydrodynamic, hydrochemical, and sedimentologic properties of the unsaturated zone under the conditions of evaporation from a shallow water table. Water beneath the salt-flat surface moves upward from the saturated zone, through a thick capillary fringe, to the unsaturated zone where it is removed by evaporation. Daily temperature fluctuations change soil suction values and seasonal variations in temperature alter the thickness of the capillary fringe. There is little change in the chemical composition of the pore water as it moves from below the water table to the capillary fringe because the filled pore spaces of the capillary fringe prevent evaporation from taking place. However, an enrichment in the heavy isotopes of hydrogen and oxygen in the groundwater, as compared to area precipitation, suggests that evaporation may have occurred earlier along the flow path. As water moves from the top of the capillary fringe into the unsaturated zone, evaporation in the partially-filled pore spaces increases the total dissolved solids content. According to the increase in chlorinity, the brine has lost over 60% of its original volume by the time it has moved to within 20 cm of the surface. Evaporation in the unsaturated zone further enriches the brine in deuterium and oxygen-18. Gypsum precipitation in the unsaturated zone depletes the shallow pore water in calcium and sulfate, relative to chloride, and forms white patches, enterolithic bands, and discontinuous lenses of pure gypsum. The sediments are made almost entirely of gypsum and dolomite. The high magnesium-to-calcium molar ratio in the brines and the poorly ordered nature of the dolomite mud in the sediment column indicate that the salt-flat dolomite formed by the alteration of a calcium carbonate precursor. A lack of lateral continuity in sediment structures and a change in sediment character from massive below the water table to laminated above indicate that the shallow salt-flat sediments were formed by vadose-zone processes rather than by sedimentation in an ancient lake.Item Hydrogeologic controls on underflow in alluvial valleys : implications for Texas water law(1988-12) Larkin, Randall G.; Sharp, John Malcolm, Jr., 1944-Groundwater flow in alluvial valleys consists of two components, baseflow and underflow. The baseflow component of the Darcy flux flows normal to the river and contributes to the surface flow. The underflow component moves downstream in the same direction as the river but at a much slower rate. Underflow is important in Texas because the conjunctive use of groundwater and surface water is regulated by controlling the diversion of underflow by wells. Land owners in Texas are legally entitled to unrestricted use of the underground water beneath their property. Stream underflow, however, has been expressly excluded from the definition of underground water. The distinction is important because it allows the State to legally restrict the non-domestic pumpage of groundwater (in an "underflow zone") near streams. Regulators are interested in controlling pumpage near rivers in order to prevent streamflow depletion. Historically, the underflow exemption has not been well recognized by the courts. In large measure, this may be due to the fact that our understanding of underflow in alluvial valleys is incomplete. If the underflow rule is to be successfully implemented, a complete understanding of the nature and occurrence of underflow is imperative. This study was initiated to: 1) determine the hydrogeologic factors that control underflow (and baseflow) in alluvial valley aquifers in Texas and the United States; and 2) to examine the suitability of the underflow criterion as a management tool for the prevention of streamflow depletion by wells. To accomplish this, a data base of 23 alluvial river basins was compiled and a 3-dimensional digital model of a hypothetical alluvial valley aquifer was constructed. Examples from the data base indicate that alluvial aquifers can be classified into three types based on the predominant regional groundwater flow direction: baseflow-dominated, underflow-dominated, and mixed flow. Flow patterns can be transient, however, and respond rapidly to changing river stage if the aquifer and the riverbed are highly permeable. Therefore, the distinction must be made between local, transient underflow and baseflow occurring near the river and regional, steady state underflow and baseflow away from the river. Underflow dominated aquifers are found in classic bedload depositional settings which are characterized by high channel gradient, high width to depth ratio, low channel sinuosity, and low river penetration. Linear regressions performed on the parameter values in the data base verify the validity of the data. The degree of correlation provides the basis for a method of estimating the predominant regional groundwater flow direction in an alluvial aquifer based on geomorphologic and morphometric data. The results from the digital model agree with the findings from the data base. Digital simulations indicate that the amount of underflow is directly related to the channel gradient, the amount of recharge, the aquifer hydraulic conductivity, and the streambed hydraulic conductivity. The riverbed hydraulic conductivity is the most critical hydraulic factor controlling the amount of underflow. The output from the model is 100 percent underflow at low values of riverbed permeability. Both the model results and published field data do not support the existence of a significant local "underflow zone" adjacent to rivers in large alluvial systems. Close to the river, the baseflow component may predominate even in regionally underflow-dominated systems due to the influence of high transverse valley gradients. There are many problems associated with the use of underflow as a management tool. The definition is vague and ambiguous. Underflow can be transient and spatially variable. Texas alluvial systems are baseflow dominated and there is probably no significant "underflow zone" near rivers. Lastly, the presence of underflow has been difficult to prove in court. It is the finding of this study that the underflow criterion is insufficient to prevent streamflow depletion by wells. The underflow rule in the Texas Water Code should be reconsidered, or perhaps abandoned, in favor of criteria that are more justifiable.Item Hydrogeological analysis of groundwater chemistry and sulfate distribution, Blanco and Hays Counties, Texas(2010-05) Andring, Megan J., 1984-; Sharp, John Malcolm, 1944-; Bennett, Philip C.; Helper, Mark A.High concentrations of sulfate in groundwater, up to ten times the amount recommended by the EPA, in Blanco and Hays Counties, Texas, are of concern as groundwater pumping and population increase. The goals of this study are to characterize the chemistry of groundwaters in Blanco and Hays Counties within the context of Texas Groundwater Management Area-9 and to determine chemically and hydrogeologically the explanation for the spatial distribution of sulfate between the Pedernales River, the Blanco River, and Onion Creek. Insights gained by examining sulfate distribution in Blanco and Hays Counties can be applied to the other counties on the Edwards-Trinity Plateau with similarly high concentrations of sulfate in groundwater. Hydrochemical data from the Cretaceous Edwards and Trinity Groups and water level measurements were used to analyze groundwater chemistry and flow. PHREEQC was used to examine whether phase changes in aquifer minerals could explain the observed geochemical patterns. COMSOL was used to develop a simplified groundwater flow model for a cross-sectional area between the Pedernales River and Onion Creek in Hays County. Water levels indicate that groundwater generally flows southeast in the study area and most streams are gaining. The groundwater flow model indicates a zone of slow-moving groundwater beneath the topographic high between the Pedernales River, the Blanco River, and Onion Creek. Chemical analyses of well data show the presence of four groundwater chemical endmembers in Groundwater Management Area-9; a Ca-Mg-HCO3 fresh endmember, a Ca-Mg-SO4 endmember, a Ca-Mg-SO4-Na-Cl endmember, and a Na-Cl endmember. High sulfate waters generally come from the Upper and Middle Trinity aquifers while fresher waters are from the Edwards aquifer. Physical and chemical analyses indicate that the zone of high sulfate in Blanco and Hays Counties may be the result of gypsum dissolution and dedolomitization in the Upper and Middle Trinity aquifers combined with low rates of groundwater flow beneath the topographic high. Groundwater flow analyses are consistent with those for the Groundwater Availability Models published for the region. Chemical analyses, specifically SO4 distributions and Ca/Mg ratios, are consistent with those found by Nance(2010) on the Edwards Plateau, farther west of the study area.Item Hydrogeology of the Albian Formation, Algeria(Texas Tech University, 1973-05) Winn, Robert MauriceNot availableItem Interactions and Implications of a Collector Well with a River in an Unconfined Aquifer with Regional Background Flow(2010-01-14) Dugat, William D., IVRanney radial collector wells consist of an array of horizontal lateral wells arranged radially around and connected to the base of a vertical well. They offer numerous advantages over traditional vertical wells with application in both the petroleum industry and hydrologic sciences. This study improved the understanding of the interaction of collector wells and the aquifers/reservoirs they tap by numerically modeling flux exchanges between a collector well and a river in an unconfined aquifer with regional background flow. Modeling demonstrated that flux along each horizontal lateral increased with distance from the vertical well stem following a third order polynomial function. Ultimately these models demonstrated that in the collector well/aquifer/river system, the pumping rate of the collector well was the dominant factor in controlling flux between the river and aquifer under various conditions. This study can be used to project the maximum allowable pumping rate without causing an initially gaining river to become a losing river.Item Karst hydrogeology and speleogenesis of Sistema Zactón, Tamaulipas, Mexico(2009-12) Gary, Marcus Orton; Sharp, John Malcolm, 1944-Understanding geologic mechanisms that form karst is of global interest. An estimated 25% of the world's population obtains water from karst aquifers and numerous major petroleum reserves are found in paleokarst reservoirs, so characterization and classification of specific types of karst is essential for resource management. Sistema Zacatón, which includes the second deepest underwater cave in the world, is hypothesized to have formed from volcanogenic karstification, defined as a process that relies on four components to initiate and develop deep, subsurface voids: a carbonate matrix, preferential groundwater flowpaths (fractures), volcanic activity that increases groundwater acidity, and groundwater flux through the system. Phases of karstification creating this modern hydrogeological environment are defined using numerous methods: field mapping, 3-D imaging of surface and aqueous environments, geophysical investigations, physical and chemical hydrogeologic characterization, and microbial analysis. Interpretation of the results yields a multi-phased speleogenetic model of the karst, with most phases occurring in the late Pleistocene. The surface rocks are carbonate travertine with Pleistocene mammoth fossils found within the rock matrix, and are interpreted as a hydrothermal travertine terrace formed as nearby volcanic activity peaked, thus representing the end member of a carbonate mass transfer system originating deep in the subsurface. The modern karst system includes a dynamic set of deep, phreatic sinkholes, also called cenotes, which propagated up through the travertine, eventually exposing hydrothermal water supersaturated with carbon dioxide to the atmosphere. In some cases these cenotes have precipitated seals of a second stage of travertine as CO₂ degassed, capping the sinkhole with a hydrologic barrier of travertine. Evidence of these barriers is observed in aqueous physical and geochemical characteristics of the cenotes, as some have high hydrologic gradients and contrasting geochemistry to those of neighboring cenotes. Investigations of electrical resistivity geophysics and underwater sonar mapping support the hypothesis of the barriers and define the morphology in intermediate and final phases of sinkhole sealing. Volcanogenic karstification is not limited to Sistema Zacatón, although the localized nature coupled with rapid and extreme degrees of karstification makes it an ideal modern analogue for classifying other karst systems as volcanogenic.Item Numerical simulation of the hydraulic parameters of an alluvial aquifer using a 3-D finite element computer model(Texas Tech University, 1990-05) Foong, Veen CheeThe study of groundwater dates back to ancient times. Historically, however, groundwater utilization preceded the understanding of its origin, occurrence, and movement. Today, the management of groundwater resources includes the allocation of groundwater supplies to competing demands and the control of water quality. As population and industrial growth rates increase, the quantity of wastes generated by humans increases. This amount of wastes has become far greater than that which the natural environment can absorb. Contamination of the subsurface water sources has thus become an increasingly alarming problem. The phenomenon of contaminant transport in groundwater has been widely studied during the past two decades.Item Resurrecting legacy code to revitalize software for groundwater research : reproducibility and robustness for the Barton Springs case, Texas(2016-12) Kwon, Nalbeat; Pierce, Suzanne Alise, 1969-; Kreitler, Charles W; Gil, YolandaAdvanced computing is becoming an indispensable part of geosciences, the interdisciplinary nature of which often requires large-scale and data-intensive numerical modeling. Groundwater in Texas is one such area that can greatly benefit from advanced decision support for understanding aquifer systems, uncertainty analysis, and policy making. However, software developed for research is often used for a relatively short period of time before it is abandoned or lost. The unintentional abandonment of software within the fast changing technological landscape makes model simulation results difficult to replicate, hindering widespread reusability and causing significant effort to be lost on redeveloping new software for researchers pursuing similar or adapted studies. These legacy codes are potentially important assets and may be resurrected and moved to an archive for long-term reuse. This research develops and tests methodologies to inform the design of best practices for documenting and preserving reproducible workflows and scientific software. Methodologies were tested with an existing codebase and assets from the Groundwater Decision Support System (GWDSS), originally developed in 2006 for participatory decision making and groundwater management. The original GWDSS provided a hybrid architecture for integrated assessment models by combining a numerical simulation code for groundwater (MODFLOW) with other systems dynamics and optimization components. Prior attempts to resurrect GWDSS were unsuccessful due to problems commonly experienced with scientific software, such as insufficient documentation and backward compatibility issues. This research experimented with two resurrection strategies: 1) Initially, a virtual machine (VM) approach to handle compatibility issues, which found similar obstacles in addition to the lack of provenance that would yield questionable results, and possibly inherent problems with the codebase due to uncurated changes made in the past. 2) Then efforts were redirected to writing a new application that replicates and improves many of the old functionalities of GWDSS, leveraging high-performance computing for batch processing of data while seeking to integrate new web-based technologies for data visualization. Ultimately, research efforts informed design and preparation of an ideal architecture that uses an open source framework and technology stack that enables users to easily access and use distributed data systems.Item Surface water recharge in karst : Edwards-Trinity Aquifers-Nueces River system(2015-05) Kromann, Jenna; Sharp, John Malcolm, Jr., 1944; Gary, Marcus O.; Johnson, Joel PThe karstic Edwards Aquifer is a primary source of water in south-central Texas for domestic, agriculture, and industrial uses. Significant recharge into the aquifer occurs as surface water streams, including the Nueces River, cross the Recharge Zone (RZ). Recharge models use data from two stream gauges, located above and below the RZ. These gauges are used to compute recharge into the aquifer; this may underestimate recharge volume because the actual water balance is complex. Synoptic gain/loss studies show that: flow rates change significantly as the river passes through extensive unconsolidated alluvium, gain/loss in reaches varies temporally, and recharge may be occurring in the Contributing Zone (CZ). From these synoptic studies, a 10-km reach of the Nueces River near Montell, TX, was identified that loses 100% of flow over the CZ during low stream flows. In this study reach, Candelaria Creek runs parallel to the dry segment of the Nueces River for 2.5 km; the creek contributes 52-64% of flow measured at the USGS recharge index gauge. The main sources of flow to the creek are two springs, hypothesized as possibly being sourced from: underflow from the Nueces River, a combination of Trinity Aquifer groundwater and river underflow, or solely groundwater from the Trinity Aquifer. To investigate recharge in the CZ and the source water for springs that contribute flow to Candelaria Creek, a variety of methods were used including: hydrograph and gain/loss analyses, potential evapotranspiration calculations, and interpretation of specific conductance, temperature, chemical, isotopic, and near surface geophysical data. The data suggest that the springs are likely sourced from both Nueces River underflow and Trinity Aquifer groundwater. Defining the source of the springs that contribute to Candelaria Creek is important to understand the complex water balance in the Nueces River and the role of underflow/storage in this system. It was found that underflow was a significant source of spring flow, but could not account for the total amount of spring flow; this suggests the Trinity Aquifer also contributes flow to the springs. A water balance estimates that recharge in the CZ at 6,213,048-9,814,814 m3 per year, which is between 0.9 to 2% of total recharge to the Edwards Aquifer and 4 to 11% of Nueces Basin recharge may be unaccounted for over the CZ during low hydrologic flow conditions. This water balance suggests that there is significant recharge occurring over the CZ and some recharge may be unaccounted for based on the current method used to calculate recharge.Item The effects of sedimentary basins on the dynamics of the East Antarctic Ice Sheet from enhanced groundwater and geothermal heat flow(2016-05) Gooch, Bradley Tyler; Blankenship, Donald D.; Dalziel, Ian W; Ghattas, Omar; Hesse, Marc A; Young, Duncan AIt is well known that ice sheets heavily influence groundwater systems, however, the impact of groundwater on ice sheet dynamics is not. This poorly understood aspect of ice-sheet hydrology is relevant to the subglacial hydrology of ice sheets lacking surface or englacial meltwater such as the East Antarctic Ice Sheet (EAIS). How groundwater systems redistribute geothermal heat at the base of an ice sheet is also largely unknown. Geothermal heat and subglacial hydrology are important basal processes controlling ice flow. Large sedimentary basins underlie the EAIS, which likely play host to many groundwater systems. I hypothesized that groundwater systems in these sedimentary basins may be the main water transport mechanism over water sheets (or films) at large scales in the interior of the ice sheet where basal melt rates are very low. I also hypothesized that these groundwater systems are likely important to the basal processes (specifically heat flux) and dynamics of the EAIS (particularly in rheological and sliding behavior). To test these, I created various one- and two-dimensional numerical models incorporating relevant datasets and conservative assumptions about the subsurface. The models ranged from simple groundwater and thermal simulations to a complex subsurface fluid and thermal model coupled to a fully dynamic ice sheet simulator. The models suggest that groundwater most likely has measurable effects on the dynamics of ice sheets like the EAIS. I have shown that probable groundwater systems underneath the interior of the EAIS can likely transport most of the meltwater produced and that groundwater can strongly affect the heat flux (positively, as well as, negatively) at the ice base under kilometers of relatively slow-moving ice. I have also not only shown that groundwater systems under the EAIS are strongly controlled by the ice sheet’s dynamics but that groundwater systems have a feedback to the ice dynamics, mostly through enhanced basal sliding and changes to the ice rheology. These results provide the justification to include groundwater in future simulations of the EAIS as well as a call to collect more data to better delineate its subsurface sedimentary basins – a critical input for groundwater and heat transport modeling.Item Water storage contributions to the excitation of polar motion(1989-05) Kuehne, John William, 1960-; Wilson, Clark R.The goal of this research was to investigate further the role of air redistribution and continental water storage changes in the excitation of both the annual and Chandler wobbles for the period 1900-85. The annual and Chandler excitations from air redistribution have been studied by Wilson and Haubrich (1976), Wahr (1982), and Hinnov and Wilson (1985). Annual excitation from water storage was estimated by Van Hylckama (1970), Hinnov and Wilson (1985), and Chao and O'Connor (1988). Chandler wobble excitation from water storage changes has been addressed only by Hinnov and Wilson (1985). This study was undertaken as a refinement to their encouraging but preliminary results.