Changes In Water Table Elevation Research Articles

Simulating water table response to proposed changes in surface water management in the C-111 agricultural basin of south Florida

As part of an effort to restore the hydrology of Everglades National Park (ENP), incremental raises in canal stage are proposed along a major canal draining south Florida called C-111, which separates ENP from agricultural lands. The study purpose was to use monitoring and modeling to investigate the effect of the proposed incremental raises in canal stage on water table elevation in agricultural lands. The objectives were to: (1) develop a MODFLOW based model for simulating groundwater flow within the study area, (2) apply the developed model to determine if the proposed changes in canal stage result in significant changes in water table elevation, root zone saturation or groundwater flooding and (3) assess aquifer response to large rainfall events. Results indicate the developed model was able to reproduce measured water table elevation with an average Nash–Sutcliffe >0.9 and Root Mean Square Error <0.05m. The model predicted that incremental raises in canal stage resulted in significant differences (p<0.05) in water table elevation. Increases in canal stage of 9 and 12cm resulted in occasional root zone saturation of low elevation sites. The model was able to mimic the rise and fall of the water table pre and post Tropical Storm Isaac of August 2012. The model also predicted that lowering canal stage at least 48h prior to large storm (>2 year return period storm), reduced water table intrusion into the root zone. We conclude that the impact of operational changes in canal stage management on root zone saturation and groundwater flooding depended on micro-topography within the field and depth of storm events. The findings of this study can be used in fine tuning canal stage operations to minimize root zone saturation and groundwater flooding of agricultural fields while maximizing environmental benefits through increased water flow in the natural wetland areas. This study also highlights the benefit of detailed field scale simulations.

Noninvasive characterization of the Trecate (Italy) crude-oil contaminated site: links between contamination and geophysical signals

The characterization of contaminated sites can benefit from the supplementation of direct investigations with a set of less invasive and more extensive measurements. A combination of geophysical methods and direct push techniques for contaminated land characterization has been proposed within the EU FP7 project ModelPROBE and the affiliated project SoilCAM. In this paper, we present results of the investigations conducted at the Trecate field site (NW Italy), which was affected in 1994 by crude oil contamination. The less invasive investigations include ground-penetrating radar (GPR), electrical resistivity tomography (ERT), and electromagnetic induction (EMI) surveys, together with direct push sampling and soil electrical conductivity (EC) logs. Many of the geophysical measurements were conducted in time-lapse mode in order to separate static and dynamic signals, the latter being linked to strong seasonal changes in water table elevations. The main challenge was to extract significant geophysical signals linked to contamination from the mix of geological and hydrological signals present at the site. The most significant aspects of this characterization are: (a) the geometrical link between the distribution of contamination and the site's heterogeneity, with particular regard to the presence of less permeable layers, as evidenced by the extensive surface geophysical measurements; and (b) the link between contamination and specific geophysical signals, particularly evident from cross-hole measurements. The extensive work conducted at the Trecate site shows how a combination of direct (e.g., chemical) and indirect (e.g., geophysical) investigations can lead to a comprehensive and solid understanding of a contaminated site's mechanisms.

Seasonal changes in peatland surface elevation recorded at GPS stations in the Red Lake Peatlands, northern Minnesota, USA

Northern peatlands appear to hold large volumes of free‐phase gas (e.g., CH4 and CO2), which has been detected by surface deformations, pore pressure profiles, and electromagnetic surveys. Determining the gas content and its impact in peat is challenging because gas storage depends on both the elastic properties of the peat matrix and the buoyant forces exerted by pore fluids. We therefore used a viscoelastic deformation model to estimate these variables by adjusting model runs to reproduce observed changes in peat surface elevation within a 1300 km2 peatland. A local GPS network documented significant changes in surface elevations throughout the year with the greatest vertical displacements associated with rapid changes in peat water content and unloadings due to melting of the winter snowpack. These changes were coherent with changes in water table elevation and also abnormal pore pressure changes measured by nests of instrumented piezometers. The deformation model reproduced these changes when the gas content was adjusted to 10% of peat volume, and Young's modulus was varied between 5 and 100 kPa as the peat profile shifted from tension to compression. In contrast, the model predicted little peat deformation when the gas content was 3% or lower. These model simulations are consistent with previous estimates of gas volume in northern peatlands and suggest an upper limit of gas storage controlled by the elastic moduli of the peat fabric.

Discontinuous Steady‐State Analytical Solutions of the Boussinesq Equation and Their Numerical Representation by Modflow

Known analytical solutions of groundwater flow equations are routinely used for verification of computer codes. However, these analytical solutions (e.g., the Dupuit solution for the steady-state unconfined unidirectional flow in a uniform aquifer with a flat bottom) represent smooth and continuous water table configurations, simulating which does not pose any significant problems for the numerical groundwater flow models, like MODFLOW. One of the most challenging numerical cases for MODFLOW arises from drying-rewetting problems often associated with abrupt changes in the elevations of impervious base of a thin unconfined aquifer. Numerical solutions of groundwater flow equations cannot be rigorously verified for such cases due to the lack of corresponding exact analytical solutions. Analytical solutions of the steady-state Boussinesq equation, associated with the discontinuous water table configurations over a stairway impervious base, are presented in this article. Conditions resulting in such configurations are analyzed and discussed. These solutions appear to be well suited for testing and verification of computer codes. Numerical solutions, obtained by the latest versions of MODFLOW (MODFLOW-2005 and MODFLOW-NWT), are compared with the presented discontinuous analytical solutions. It is shown that standard MODFLOW-2005 code (as well as MODFLOW-2000 and older versions) has significant convergence problems simulating such cases. The problems manifest themselves either in a total convergence failure or erroneous results. Alternatively, MODFLOW-NWT, providing a good match to the presented discontinuous analytical solutions, appears to be a more reliable and appropriate code for simulating abrupt changes in water table elevations.

Reversible rock-slope deformations caused by cyclic water-table fluctuations in mountain slopes of the Central Alps, Switzerland

Within the framework of the Gotthard Base Tunnel Project in the Central Alps, Switzerland, geodetic monitoring networks were installed above the tunnel trajectory in alpine valleys. Natural ground-surface deformation recorded in the years prior to the tunneling excavation was seen to contain an unexpectedly large cyclical component of horizontal strain across the valleys, which was seasonal and appeared to be due to elastic processes. The strain is strongly correlated with snow melt and rainstorm precipitation, suggesting the implied rock-mass deformation is driven by changes in water-table elevation within adjacent mountain slopes. The horizontal strains are of the order of 1–2 · 10–5, which is close to the design limits that can be accommodated by hydropower arch dams in the study area. This study investigates these processes in detail and describes a new mathematical model (REROD), which is able to accurately reproduce and predict such natural rock-slope displacements. The model implements a transfer-function approach to predict the valley-crossing strains from rainfall and winter snow height data recorded at nearby meteorological stations. It has been used to estimate and remove the natural strain signal from the net recorded deformation so as to resolve the component due to tunneling.

A novel technique for estimating wetting front migration rates through the vadose zone based on changes in groundwater velocity

► A novel technique to estimate wetting front migration rates was field tested. ► A groundwater velocity probe was used to estimate wetting front migration rates. ► This technique was comparable to conventional techniques. ► Applications include optimizing infiltration rates and identify vadose zone clogging. Managed aquifer recharge in unconfined aquifers often requires careful monitoring of infiltration rates to optimize residence times in the unsaturated zone to enhance biodegradation and to identify clogging. Conventional methods of monitoring infiltration performance commonly rely on interpreting changes in soil moisture or changes in water table elevation using in situ devices. This paper describes a novel technique based on changes in groundwater velocity near the infiltration zone. Two field experiments were conducted that involved imposing step increases in the rate of recharge to a sandy, 10 m thick vadose zone, following cessation of infiltration over several days and different pre-existing soil moisture conditions. Estimated wetting front migration rates were comparable for the groundwater velocity (7.7 m day −1 ), water table elevation (7.3 m day −1 ) and soil moisture (8.0 m day −1 ) techniques investigated. Further work is required to validate the groundwater velocity technique at other field sites, and extend its use, e.g. to optimize infiltration rates and identify vadose zone clogging.

Influence of Fire and Water Regimes on Pineland Bird Assemblages

At the broadest spatial scales, the distribution of south Florida slash pine (Pinus elliottii var. densa Little and Dorman) is limited by variation in fire and hydrological regimes, occurring only in relatively dry areas and succeeding to hardwood hammocks when fire is absent. These same forces also appear important in driving smaller-scale variation in the structure and composition of slash-pine forests. Important gaps remain, however, in our understanding of how plants and animals in slash-pine ecosystems respond to variation in fire and hydrological regimes. We addressed this issue for one taxon — landbirds — by estimating density at 285 locations in southwest Florida that differed in fire history and water-table elevation. Bird densities during the breeding season and during the winter did not vary appreciably as a function of either fire history or water-table elevation, and neither did vegetation structure at our survey locations. Birds and plants in this fire-climax forest are both resilient and resistant to changes brought about by frequent, low-intensity fire, and we suspect that significant effects of variation in fire history are only observable under extreme conditions (e.g., complete fire suppression) outside of the range of variation that we sampled. Water-table elevation had a stronger, albeit still small, effect on bird densities and vegetation structure, but the effects were difficult to generalize. Sampling across a broader range of hydrological conditions may yield valuable insight into the structure of pineland bird assemblages, especially given the likelihood that ecosystem restoration efforts in south Florida will produce substantial changes in water-table elevation.

Controls on the spatial and temporal variability of 222Rn in riparian groundwater in a lowland Chalk catchment

Radon is a powerful tracer of stream–aquifer interactions. However, it is important to consider the source and behaviour of radon in groundwater when interpreting observations of river radon in relation to groundwater discharge. Here we characterise the variability in groundwater radon concentrations in the riparian zone of a Chalk catchment. Groundwater 222 Rn (radon) concentrations were determined in riparian zone boreholes at two sites in the Lambourn catchment, Berkshire, UK, over a 2 year period. In addition, borehole core material was analysed for 226 Ra (radium) and to determine radon emanation. Radon and radium concentrations and radon emanation were found to change with depth and temporal variations in groundwater radon concentrations were found at different scales. The abundance of radium and emanation of radon increased nearer the surface leading to greater groundwater radon concentrations. It is shown that seasonal changes in water table elevation can to lead to variable radon concentrations in groundwater as zones of differing radon production become hydraulically active. Groundwater radon concentrations in shallow piezometers were found to respond to both seasonal changes in the water table and individual rainfall events. Riparian sources of radon can be variable and are therefore potentially influential in the radon signals observed in rivers and should be properly characterised when interpreting river radon inputs.

Advances in Canadian Peatland Hydrology, 2003-2007

Peatlands represent over 90% of Canadian wetlands and are the focus of considerable hydrological and biogeochemical research. Research on evapotranspiration (ET) has shown that it can exceed annual precipitation (P) where there are replenishing flood events. Evaporation from open water ponds in boreal peatlands exceeds ET from vegetated riparian zones by about two times, but surrounding forests can shelter small ponds by reducing turbulence. In an open bog, evaporation was modelled by separating the surface into vascular vegetation, hummock moss and hollow moss surfaces, and showed that vascular plants contribute 60-80% of ET, mosses making up the remainder with hummock mosses dominant over hollows. Runoff from peatlands is enhanced by features ranging from headwater swamps, ice-cored peat plateaus, patchy arctic wetlands and even sections of riverine peatlands. Groundwater fluxes can be quite erratic, and depend on transient properties of the peat that depend on moisture content (e.g., unsaturated hydraulic conductivity) to unsteady saturated hydraulic properties (e.g., hydraulic conductivity, specific yield) caused by peat compression and dilation associated with water storage changes. Surface elevation adjustments can result in a more stable depth to water table, increase evaporation losses, increase methane emission, and attenuate pore-water concentration of contaminants. Research on Canadian peatlands has also made significant methodological advances, including measurement of hydraulic properties of living mosses and peat pore-water and pore dimension characteristics. A considerable multi-annual effort has also been made in evaluating carbon dynamics from Canadian peatlands. Summer moisture availability is important to determining carbon fluxes with some peatlands experiencing enhanced productivity following drought (water table drawdown). Sudden changes in water table elevation promote DOC production and export. Methane bubbles confound hydraulic gradients and flows by creating local pockets of pressure, which are then released episodically when the entrapped gas reaches a threshold content. Canadian peatland hydrology continues to be actively researched in lab, field and modelling studies.

Regional groundwater flow in mountainous terrain: Three‐dimensional simulations of topographic and hydrogeologic controls

This study uses numerical simulations to define the salient controls on regional groundwater flow in 3‐D mountainous terrain by systematically varying topographic and hydrogeologic variables. Topography for idealized multiple‐basin mountainous terrain is derived from geomatic data and literature values. Water table elevation, controlled by the ratio of recharge to hydraulic conductivity, largely controls the distribution of recharged water into local, regional, and perpendicular flow systems, perpendicular flow being perpendicular to the regional topographic gradient. Both the relative (%) and absolute (m3/d) values of regional flow and perpendicular flow are examined. The relationship between regional flow and water table elevation is highly nonlinear. With lower water table elevations, relative and absolute regional flow dramatically increase and decrease, respectively, as the water table is lowered further. However, for higher water table elevations above the top of the headwater stream, changes in water table elevation have little effect on regional flow. Local flow predominates in high water table configurations, with regional and perpendicular flow &lt;15% and &lt;10%, respectively, of total recharge in the models tested. Both the relative and the maximum absolute regional flow are directly controlled by the degree of incision of the mountain drainage network; the elevation of mountain ridges is considerably less important. The percentage of the headwater stream with perennial streamflow is a potentially powerful indicator of regional flow in all water table configurations and may be a good indicator of the susceptibility of mountain groundwater systems to increased aridity.

Groundwater Nitrate Spatial and Temporal Patterns and Correlations: Influence of Natural Controls and Nitrogen Management

To use shallow groundwater NO3–N concentration as an indicator of groundwater quality requires understanding its patterns, correlations, and controls across space and time. Within a study comparing variable‐rate and uniform N management, our objectives were to determine groundwater NO3–N patterns and correlations at various spatial and temporal scales and their association with natural controls and N management. Experiments in a random, complete block design were conducted in a 2‐yr crop rotation in North Carolina that included one variable‐rate and two uniform N management treatments to wheat (Triticum aestivumL.) and corn (Zea maysL.). We measured groundwater NO3–N and depth every 2 wk at 60 well nests, sampling the 0.9‐ to 3.7‐m depth. Field‐mean NO3–N varied with time from 5.5 to 15.3 mg NO3–N L−1These variations were correlated primarily with concurrent changes in water table elevation and depth. Mean NO3–N exhibited two preferred states: high when the water table was shallow and low when the water table was deep. Temporal NO3–N fluctuations greatly exceeded treatment effects. Treatments appeared to affect NO3–N temporal covariance structure. Groundwater NO3–N spatial patterns and correlations were associated mostly with saturated hydraulic conductivity and water table fluctuations and appeared influenced by subsurface lateral flow. When treatment effects became consistently significant later in the study, they overrode natural controls, and NO3–N was spatially uncorrelated or exhibited shorter spatial correlation ranges and patterns associated predominantly with treatments.

Groundwater flow patterns in a large peatland

Groundwater flow patterns and geochemistry were studied in the Mer Bleue bog, near Ottawa, Ontario, Canada. Groundwater flow patterns alternated between recharge, i.e. head gradients producing flow from the surface of the peatland to the deeper peat, and discharge, i.e. head gradients indicating flow from the deeper peat towards the surface of the peatland, during the summer of 1998. The patterns were controlled by changes in precipitation, evapotranspiration and the differential head response of catotelm peat (lower layer) to changes in water table elevation. Above-average rainfall in the spring created recharge patterns of groundwater flow in the peatland. Evapotranspiration exceeded precipitation for a three-week period in mid-summer decreasing head at the water table and reversing flow from recharge to discharge. A sustained moisture deficit maintained a flow reversal for 32 days, until a 46 mm rainfall raised the water-table, reversing the vertical hydraulic gradients and restoring recharge flow. The mixing of meteoric water and deeper groundwater controls geochemical profiles. Diffusion modeling shows that the peatland is a long-term recharge system. However, electrical conductivity and cation concentrations in peat pore-waters increase (up to 60%) during a flow reversal, and then decrease when recharge conditions are re-established. The redistribution of substrates from reversed flow is likely important to peatland biogeochemical function.

Response of Bog and Fen Plant Communities to Warming and Water-Table Manipulations

Large-scale changes in climate may have unexpected effects on ecosystems, given the importance of climate as a control over almost all ecosystem attributes and internal feedbacks. Changes in plant community productivity or composition, for example, may alter ecosystem resource dynamics, trophic structures, or disturbance regimes, with subsequent positive or negative feedbacks on the plant community. At northern latitudes, where increases in temperature are expected to be greatest but where plant species diversity is relatively low, climatically mediated changes in species composition or abundance will likely have large ecosystem effects. In this study, we investigated effects of infrared loading and manipulations of water-table elevation on net primary productivity of plant species in bog and fen wetland mesocosms between 1994 and 1997. We removed 27 intact soil monoliths (2.1 m2 surface area, 0.5–0.7 m depth) each from a bog and a fen in northern Minnesota to construct a large mesocosm facility that allows for direct manipulation of climatic variables in a replicated experimental design. The treatment design was a fully crossed factorial with three infrared-loading treatments, three water-table treatments, and two ecosystem types (bogs and fens), with three replicates of all treatment combinations. Overhead infrared lamps caused mean monthly soil temperatures to increase by 1.6–4.1°C at 15-cm depth during the growing season (May–October). In 1996, depths to water table averaged −11, −19, and −26 cm in the bog plots, and 0, −10, and −19 cm in the fen plots. Annual aboveground net primary production (ANPP) of bryophyte, forb, graminoid, and shrub life-forms was determined for the dominant species in the mesocosm plots based on species-specific canopy/biomass relationships. Belowground net primary production (BNPP) was estimated using root in-growth cores. Bog and fen communities differed in their response to infrared loading and water-table treatments because of the differential response of life-forms and species characteristic of each community. Along a gradient of increasing water-table elevation, production of bryophytes increased, and production of shrubs decreased in the bog community. Along a similar gradient in the fen community, production of graminoids and forbs increased. Along a gradient of increasing infrared loading in the bog, shrub production increased whereas graminoid production decreased. In the fen, graminoids were most productive at high infrared loading, and forbs were most productive at medium infrared loading. In the bog and fen, BNPP:ANPP ratios increased with warming and drying, indicating shifts in carbon allocation in response to climate change. Further, opposing responses of species and life-forms tended to cancel out the response of production at higher levels of organization, especially in the bog. For example, total net primary productivity in the bog did not differ between water-table treatments because BNPP was greatest in the dry treatment whereas ANPP was greatest in the wet treatment. The differential responses of species, life-forms, and above- and belowground biomass production to the treatments suggest that bog and fen plant communities will change, in different directions and magnitudes, in response to warming and changes in water-table elevation. Further, results of this and complementary research indicate that these peatlands may mediate their energy, carbon, and nutrient budgets through differential responses of the plant communities. Thus, predictions of the response of peatlands to changes in climate should consider differences in plant community structure, as well as biogeochemistry and hydrology, that characterize and differentiate these two ecosystems.

RESPONSE OF BOG AND FEN PLANT COMMUNITIES TO WARMING AND WATER-TABLE MANIPULATIONS

Large-scale changes in climate may have unexpected effects on ecosystems, given the importance of climate as a control over almost all ecosystem attributes and internal feedbacks. Changes in plant community productivity or composition, for example, may alter ecosystem resource dynamics, trophic structures, or disturbance regimes, with subsequent positive or negative feedbacks on the plant community. At northern latitudes, where increases in temperature are expected to be greatest but where plant species diversity is relatively low, climatically mediated changes in species composition or abundance will likely have large ecosystem effects. In this study, we investigated effects of infrared loading and manipulations of water-table elevation on net primary productivity of plant species in bog and fen wetland mesocosms between 1994 and 1997. We removed 27 intact soil monoliths (2.1 m2 surface area, 0.5–0.7 m depth) each from a bog and a fen in northern Minnesota to construct a large mesocosm facility that allows for direct manipulation of climatic variables in a replicated experimental design. The treatment design was a fully crossed factorial with three infrared-loading treatments, three water-table treatments, and two ecosystem types (bogs and fens), with three replicates of all treatment combinations. Overhead infrared lamps caused mean monthly soil temperatures to increase by 1.6–4.1°C at 15-cm depth during the growing season (May–October). In 1996, depths to water table averaged −11, −19, and −26 cm in the bog plots, and 0, −10, and −19 cm in the fen plots. Annual aboveground net primary production (ANPP) of bryophyte, forb, graminoid, and shrub life-forms was determined for the dominant species in the mesocosm plots based on species-specific canopy/biomass relationships. Belowground net primary production (BNPP) was estimated using root in-growth cores. Bog and fen communities differed in their response to infrared loading and water-table treatments because of the differential response of life-forms and species characteristic of each community. Along a gradient of increasing water-table elevation, production of bryophytes increased, and production of shrubs decreased in the bog community. Along a similar gradient in the fen community, production of graminoids and forbs increased. Along a gradient of increasing infrared loading in the bog, shrub production increased whereas graminoid production decreased. In the fen, graminoids were most productive at high infrared loading, and forbs were most productive at medium infrared loading. In the bog and fen, BNPP:ANPP ratios increased with warming and drying, indicating shifts in carbon allocation in response to climate change. Further, opposing responses of species and life-forms tended to cancel out the response of production at higher levels of organization, especially in the bog. For example, total net primary productivity in the bog did not differ between water-table treatments because BNPP was greatest in the dry treatment whereas ANPP was greatest in the wet treatment. The differential responses of species, life-forms, and above- and belowground biomass production to the treatments suggest that bog and fen plant communities will change, in different directions and magnitudes, in response to warming and changes in water-table elevation. Further, results of this and complementary research indicate that these peatlands may mediate their energy, carbon, and nutrient budgets through differential responses of the plant communities. Thus, predictions of the response of peatlands to changes in climate should consider differences in plant community structure, as well as biogeochemistry and hydrology, that characterize and differentiate these two ecosystems.

Groundwater Quality under Conventional and No Tillage: I. Nitrate, Electrical Conductivity, and pH

AbstractThe use of conservation tillage is increasing in North America, but information on its effect on water quality in cold climatic regions is limited. To obtain such information, the effect of no‐tillage (NT) and conventional tillage (CT) treatments on nitrate‐nitrogen (NO3‐N) concentration, specific electrical conductivity (EC), and pH in shallow groundwater (1.2, 1.8, 3.0, and 4.6 m depths) was studied over four successive crop years in corn fields (loam soil) of approximately 3 ha each, located in eastern Ontario. Water table elevation was also monitored during three crop years. Average NO3‐N concentration at the 1.2, 1.8, and 4.6 m depths was consistently higher under CT than under NT in every crop year and every season. However, the effect of tillage was not significant at P &lt; 0.05. Nitrate concentration decreased significantly with depth. It was about two to three times the drinking water limit of 10 mg/L as NO3‐N at the 1.2, 1.8, and 3.0 m depths. At the 4.6 m depth, NO3‐N concentrations were mostly low but increased with time. Changes in water table elevation appeared to affect NO3‐N concentrations at the 1.2 m depth under NT only. At a given depth, EC and pH of groundwater were not affected by tillage treatment. However, within each tillage treatment, values increased significantly with depth. Results from this study indicated a large spatial variability in NO3‐N and EC values in groundwater, which could have masked small tillage effects. More intensive temporal and spatial sampling may be required to establish tillage treatment effects, if any.

Multiphase flow with a simplified model for oil entrapment

A computationally simple procedure is described to model effects of oil entrapment on three-phase permeability-saturation-capillary pressure relations. The model requires knowledge of airwater saturation-capillary pressure relations, which are assumed to be nonhysteretic and are characterized by Van Genuchten's parametric model; scaling factors equal to the ratio of water surface tension to oil surface tension and to oil-water interfacial tension; and the maximum oil (also referred to as nonwetting liquid in a three-phase medium) saturation which would occur following water flooding of oil saturated soil. Trapped nonwetting liquid saturation is predicted as a function of present oil-water and air-oil capillary pressures and minimum historical water saturation since the occurrence of oil at a given location using an empirically-based algorithm. Oil relative permeability is predicted as a simple function of apparent water saturation (sum of actual water saturation and trapped oil saturation) and free oil saturation (difference between total oil and trapped oil saturation), and water relative permeability is treated as a unique function of actual water saturation. The proposed method was implemented in a two-dimensional finite-element simulator for three-phase flow and component transport, MOFAT. The fluid entrapment model requires minimal additional computational effort and computer storage and is numerically robust. The applicability of the model is illustrated by a number of hypothetical one- and two-dimensional simulations involving infiltration and redistribution with changes in water-table elevations. Results of the simulations indicate that the fraction of a hydrocarbon spill that becomes trapped under given boundary conditions increases as a nonlinear function of the maximum trapped nonwetting liquid saturation. Dense organic liquid plumes may exhibit more pronounced effects of entrapment due to the more dynamic nature of flow, even under static water table conditions. Disregarding nonwetting fluid entrapment may lead to significant errors in predictions of immiscible plume migration.

Potential for water-table excursions induced by seismic events at Yucca Mountain, Nevada

Research Article| December 01, 1991 Potential for water-table excursions induced by seismic events at Yucca Mountain, Nevada Charles R. Carrigan; Charles R. Carrigan 1Earth Science Department (L-206), Lawrence Livermore National Laboratory, Livermore, California 94550 Search for other works by this author on: GSW Google Scholar Geoffrey C. P. King; Geoffrey C. P. King 2Institut de Physique du Globe, 5, rue René Descartes, 67084 Strasbourg, France Search for other works by this author on: GSW Google Scholar George E. Barr; George E. Barr 3Sandia National Laboratories, Albuquerque, New Mexico 87185 Search for other works by this author on: GSW Google Scholar Nathan E. Bixler Nathan E. Bixler 3Sandia National Laboratories, Albuquerque, New Mexico 87185 Search for other works by this author on: GSW Google Scholar Author and Article Information Charles R. Carrigan 1Earth Science Department (L-206), Lawrence Livermore National Laboratory, Livermore, California 94550 Geoffrey C. P. King 2Institut de Physique du Globe, 5, rue René Descartes, 67084 Strasbourg, France George E. Barr 3Sandia National Laboratories, Albuquerque, New Mexico 87185 Nathan E. Bixler 3Sandia National Laboratories, Albuquerque, New Mexico 87185 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1991) 19 (12): 1157–1160. https://doi.org/10.1130/0091-7613(1991)019<1157:PFWTEI>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Charles R. Carrigan, Geoffrey C. P. King, George E. Barr, Nathan E. Bixler; Potential for water-table excursions induced by seismic events at Yucca Mountain, Nevada. Geology 1991;; 19 (12): 1157–1160. doi: https://doi.org/10.1130/0091-7613(1991)019<1157:PFWTEI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The possibility that 100-200 m changes in water-table elevation can be mechanically induced by earthquakes is a consideration in site studies of a potential high-level nuclear waste repository at Yucca Mountain, Nevada. However, numerical simulations of tectonohydrologic coupling involving earthquakes typical of the Basin and Range province produce 2-3 m excursions of a water table that is 500 m below the land surface. Even displacements corresponding to extraordinary seismic events drive water-table excursions of less than 20 m. Flow resulting from earthquake-induced pore-pressure fields below the water table tends to be mainly horizontal; vertical flows that cause changes of the level of the water table are secondary. Strongly anisotropic permeability, intended to enhance vertical flow within fault zones, only doubles water-table rise in the models considered. These simulations of water-table rise compare well with observations following large earthquakes in the Basin and Range. Our models suggest that exceptional hydrologic and/or tectonic conditions would be required to produce substantially larger water-table rises. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Construction and Performance of Large Automatic (Nonweighing) Lysimeters

ABSTRACT THE construction of 12 large, nonweighing lysimeters with automatic water table controls is described. Three distinct layers of the Hecla loamy fine sand profile were used to reconstruct the natural soil profile in the lysimeters. The controls are automatically operated with time clocks and float switches to maintain selected water table levels. The system is capable of replacing evapo-transpiration losses of up to 2 cm every 24 h and of removing excess profile water of up to 4 cm per 24-h period. The performance of the system with respect to changes in water table elevation due to different precipitation and air temperatures is shown. The system has functioned satisfactorily for 4 yr with minimum attention and maintenance.