Thomas M. Williams

Clemson University

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Daniel R. Hitchcock

Clemson University

Devendra M. Amatya

Southern Research Station

Josep Mas‐Pla

University of Girona

R. Bernhart Owen

Hong Kong Baptist University

John F. McCarthy

Central Arkansas Veterans Healthcare System

T.‐C. Jim Yeh

University of Arizona

N. Breward

British Geological Survey

Anand D. Jayakaran

GC Systems (United States)

Thomas H. Epps

Craft Engineering Associates (United States)

Bo Song

Kunming Institute of Botany

Cooperative Institutions

British Geological Survey

Clemson University

US Forest Service

Instituto de Investigación Geológico y Energético

College of Charleston

University of Tennessee at Knoxville

University of Georgia

Institute of Geological Sciences

Southern Research Station

Weatherford College

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Environmental Geochemistry and Health (2000)

Thomas M. Williams A Apostol Conrado R. Miranda

Cinnabar

Mercury

Methylmercury

10.1023/a:1006715304794

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Citations (16)

Multifractal versus monofractal analysis of wetland topography

Stochastic Environmental Research and Risk Assessment (2000)

Ioulia Tchiguirinskaia Siliang Lu Fred J. Molz Thomas M. Williams D. Lavallée

Multifractal system

Elevation (ballistics)

Hurst exponent

10.1007/s004770050002

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Citations (35)

Recovering the Effects of Subgrid Heterogeneity in Simulations of Radionuclide Transport Through Fractured Media

Frontiers in Earth Science (2021)

Thomas M. Williams Jordi Sanglas Paolo Trinchero Guanqun Gai Scott Painter

Groundwater flow and contaminant transport through fractured media can be simulated using Discrete Fracture Network (DFN) models which provide a natural description of structural heterogeneity. However, this approach is computationally expensive, with the large number of intersecting fractures necessitated by many real-world applications requiring modeling simplifications to be made for calculations to be tractable. Upscaling methods commonly used for this purpose can result in some loss of local-scale variability in the groundwater flow velocity field, resulting in underestimation of particle travel times, transport resistance and retention in transport calculations. In this paper, a transport downscaling algorithm to recover the transport effects of heterogeneity is tested on a synthetic Brittle Fault Zone model, motivated by the problem of large safety assessment calculations for geological repositories of spent nuclear fuel. We show that the variability in the local-scale velocity field which is lost by upscaling can be recovered by sampling from a library of DFN transport paths, accurately reproducing DFN transport statistic distributions and radionuclide breakthrough curves in an upscaled model.

Statistic

10.3389/feart.2020.586247

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Citations (0)

Curve Number Derivation for Watersheds Draining Two Headwater Streams in Lower Coastal Plain South Carolina, USA

JAWRA Journal of the American Water Resources Association (2013)

Thomas H. Epps Daniel R. Hitchcock Anand D. Jayakaran Drake R. Loflin Thomas M. Williams

Abstract The objective of this study was to assess curve number ( CN ) values derived for two forested headwater catchments in the Lower Coastal Plain ( LCP ) of South Carolina using a three‐year period of storm event rainfall and runoff data in comparison with results obtained from CN method calculations. Derived CN s from rainfall/runoff pairs ranged from 46 to 90 for the Upper Debidue Creek ( UDC ) watershed and from 42 to 89 for the Watershed 80 (WS80). However, runoff generation from storm events was strongly related to water table elevation, where seasonally variable evapotranspirative wet and dry moisture conditions persist. Seasonal water table fluctuation is independent of, but can be compounded by, wet conditions that occur as a result of prior storm events, further complicating flow prediction. Runoff predictions for LCP first‐order watersheds do not compare closely to measured flow under the average moisture condition normally associated with the CN method. In this study, however, results show improvement in flow predictions using CN s adjusted for antecedent runoff conditions and based on water table position. These results indicate that adaptations of CN model parameters are required for reliable flow predictions for these LCP catchments with shallow water tables. Low gradient topography and shallow water table characteristics of LCP watersheds allow for unique hydrologic conditions that must be assessed and managed differently than higher gradient watersheds.

Antecedent moisture

Coastal plain

Table (database)

10.1111/jawr.12084

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Citations (29)

Authigenesis of ferric oolites in superficial sediments from Lake Malawi, Central Africa

Chemical Geology (1990)

Thomas M. Williams R. Bernhart Owen

Ironstone

Silt

10.1016/0009-2541(90)90066-g

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Citations (17)

Field Tracer Tests on the Mobility of Natural Organic Matter in a Sandy Aquifer

Water Resources Research (1996)

John F. McCarthy Baohua Gu Liyuan Liang Josep Mas‐Pla Thomas M. Williams

The field‐scale transport of natural organic matter (NOM) was examined in a two‐well forced gradient injection experiment in a sandy, coastal plain aquifer in Georgetown, South Carolina. Spatial moments described the migration of the center of mass of NOM and conservative tracer. Temporal moments were used to estimate mass loss and retardation of the NOM along a transect of six sampling locations at two depths and at the withdrawal well. Large differences were observed in transport behavior of different subcomponents of NOM. Larger and more strongly binding NOM components in the injection solution are postulated to adsorb and displace weakly binding, low‐molecular weight NOM in groundwater. Conversely, NOM components that were similar to the groundwater NOM were transported almost conservatively, presumably due to “passivation” of the aquifer by previously adsorbed components of the groundwater NOM. NOM may thus exhibit two types of effects on contaminant dynamics in the subsurface. When the equilibria between solution and solid phase NOM is disrupted by introduction of a novel source of NOM, descriptions of the multicomponent transport process are complex and predictive modeling is problematic. Because of the differences in transport behavior of NOM subcomponents, the chemical properties and, more importantly, the functional behavior of NOM with respect to contaminant migration will vary with time and distance along a flow path. However, when groundwater NOM exists at a steady state with respect to adsorption on aquifer surfaces, the migration of NOM, and the contaminant‐NOM complex, may be approximated as the transport of a conservative solute.

TRACER

Natural Organic Matter

10.1029/96wr00285

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Citations (71)

Analyses of Slug Tests and Hydraulic Conductivity Variations in the Near Field of a Two‐Well Tracer Experiment Site

Ground Water (1997)

Josep Mas‐Pla T.‐C. Jim Yeh Thomas M. Williams John F. McCarthy

Abstract Three‐hundred eight slug tests were conducted in a 5 × 5 m area in a coastal, sandy aquifer at the Georgetown site in South Carolina to characterize three‐dimensional aquifer heterogeneity. Methods developed by Hvorslev, Bouwer and Rice, and Cooper et al. were employed to estimate hydraulic conductivity values from the slug test data. These three methods produced similar spatial distributions of the hydraulic conductivity but quite different values. Overall, the method of Cooper et al. produces higher conductivity values in high permeability zones but lower values in low permeability areas than the Hvorslev method. Variances of the natural log of conductivity values derived from Hvorslev's and Bouwer and Rice's methods agree with those in the other aquifers under similar depositional environments. However, the variance calculated for the data based on the method of Cooper et al. appears unreasonably large. Despite these differences, histograms of the three sets of conductivity values exhibit bimodal distributions, reflecting stratification of the aquifer. Geostatistical analyses show that correlation lengths and statistical anisotropy of the hydraulic conductivity spatial structure varies with depth.

Slug test

10.1111/j.1745-6584.1997.tb00110.x

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Citations (16)

Characterization of Storm Flow Dynamics of Headwater Streams in the South Carolina Lower Coastal Plain¹

JAWRA Journal of the American Water Resources Association (2012)

Thomas H. Epps Daniel R. Hitchcock Anand D. Jayakaran Drake R. Loflin Thomas M. Williams

Epps, Thomas H., Daniel R. Hitchcock, Anand D. Jayakaran, Drake R. Loflin, Thomas M. Williams, and Devendra M. Amatya, 2012. Characterization of Storm Flow Dynamics of Headwater Streams in the South Carolina Lower Coastal Plain. Journal of the American Water Resources Association (JAWRA) 1‐14. DOI: 10.1111/jawr.12000 Abstract: Hydrologic monitoring was conducted in two first‐order lower coastal plain watersheds in South Carolina, United States, a region with increasing growth and land use change. Storm events over a three‐year period were analyzed for direct runoff coefficients (ROC) and the total storm response (TSR) as percent rainfall. ROC calculations utilized an empirical hydrograph separation method that partitioned total streamflow into sustained base flow and direct runoff components. ROC ratios ranged from 0 to 0.32 on the Upper Debidue Creek (UDC) watershed and 0 to 0.57 on Watershed 80 (WS80); TSR results ranged from 0 to 0.93 at UDC and 0.01 to 0.74 at WS80. Variability in event runoff generation was attributed to seasonal trends in water table elevation fluctuation as regulated by evapotranspiration. Groundwater elevation breakpoints for each watershed were identified based on antecedent water table elevation, streamflow, ROCs, and TSRs. These thresholds represent the groundwater elevation above which event runoff generation increased sharply in response to rainfall. For effective coastal land use decision making, baseline watershed hydrology must be understood to serve as a benchmark for management goals, based on both seasonal and event‐based surface and groundwater interactions.

Coastal plain

10.1111/jawr.12000

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Citations (32)

Rare earth elements in rift-hosted ferromanganese nodules, Malawi, Central Africa

Journal of African Earth Sciences (and the Middle East) (1993)

Thomas M. Williams

Ferromanganese

Nodule (geology)

Rare-earth element

10.1016/0899-5362(93)90108-3

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