R-3 Repository :: Browsing by Author "Bedient, Philip B."

Browsing by Author "Bedient, Philip B."

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1D and 2D Methods for Modeling Floodplains under Storm Surge Conditions
(2011) Stepinski, Emilia; Bedient, Philip B.
This study evaluates a 1D and a 2D method for analyzing the combined effect of inland rainfall and hurricane-induced storm surge on a coastal floodplain. Horsepen Bayou near Clear Lake, southeast of Houston, Texas is vulnerable to storm surge, which can travel upstream into the Bayou and exacerbate flooding outside the designated floodplain. However, the current 100-year floodplain for this area is delineated using a 1D model without direct storm surge inputs. Additionally, floodplains with flat topography, like Horsepen, could be modeled more accurately using 2D models, instead of the traditional 1D approach. A 1D HEC-RAS model and a 2D XPSWMM model are used to compare the resulting floodplain from three historical storms and one synthetic storm. When compared to actual FEMA flood claims, the floodplains calculated by the 2D model are more representative of inundation hazard in Horsepen and therefore a better tool for evaluating flooding in the area.
A Distributed Hydrologic Model of The Woodlands, TX: Modeling Hydrologic Effects of Low Impact Development
(2012-09-05) Doubleday, George; Bedient, Philip B.; Li, Qilin; Raun, Loren H.
This thesis utilizes a distributed hydrologic model to predict hydrologic effects of Low Impact Development (LID), and also analyzes runoff from small sub-areas within the watershed. City planners and developers rely on accurate hydrologic models, which enable them to design flood-proof developments and effectively mitigate flooding downstream. Common hydrologic models use a lumped approach, which averages the physical characteristics of basins for model calculations, limiting their ability to estimate runoff within the basin. In contrast, distributed hydrologic models, which divide the watershed into a grid system, can be used to predict runoff at any location within the watershed. The fully distributed hydrologic model, VfloTM, is used to model stormwater runoff in The Woodlands, TX watershed, and to demonstrate the effectiveness of the master planned community. This thesis also suggests that a calibrated VfloTM model can accurately predict stormwater runoff from small sub-areas within a watershed.
A distributed-site model for non-equilibrium dissolution of multi-component residually trapped NAPL in a column test
(1997) Nelson, Paul David; Bedient, Philip B.
This thesis addresses the modeling of the dissolution of residually-trapped multi-component non-aqueous phase liquids (NAPLs) from a porous medium. As part of this work, a model was constructed in which the mass transfer behavior of the NAPL is characterized by a probability density function (pdf) which describes the initial distribution of residual NAPL "blob" volumes. Mass transfer from these trapped NAPL "spheres" is simulated using an empirical relationship for the Sherwood Number, a linear concentration driving force, and multi-component solubility effects. This "Distributed-Site" model is then used to match two sets of dissolution data from a laboratory column test.
A dynamic hydraulic floodplain map prediction tool for flood alert in a coastal urban watershed considering storm surge issues
(2008) Fang, Zheng; Bedient, Philip B.
Flood Alert System (FAS2) incorporates adjusted real-time NEXRAD radar data, GIS, hydrologic models and the Internet to provide advanced warning to the Texas Medical Center (TMC) in Houston, Texas. It has been tested during 2006 season with excellent performance and was used as a platform to develop a real-time hydraulic prediction tool---the Floodplain Map Library (FPML) system. FPML provides inundation maps in near real time linking with NEXRAD radar over the watershed. FPML is also compatible with storm surge input in order to predict inundation maps during extreme coastal weather conditions, which will improve emergency personnel's ability to initiate evacuation strategies at many levels.
A hydrogeologic database for stochastic groundwater modeling with hydrogeologic environment-specific applications
(1989) Hopkins, Loren Palmer; Bedient, Philip B.
The development of a method to restrict the land disposal of hazardous waste is an area of great concern for the United States Environmental Protection Agency. A proposed method is to determine allowable concentrations, below cancer limits, of specific chemical contaminants slated for land disposal based on the results of a Monte Carlo type contaminant groundwater transport model. The proposed regulatory model does not account for site specific conditions because the hydrogeologic environment specific data required has not previously been available. A hydrogeologic database is developed and analyzed for specific environments. The behavior of the proposed regulatory model is examined using the hydrogeologic environment specific information as input.
A method to model passive oxygen reaeration in naturally attenuating plumes using Fick's Law
(1998) Yewdall, Catherine Jennifer; Bedient, Philip B.
To physically represent oxygen reaeration in contaminant fate and transport modeling Fick's Second Law of Diffusion is numerically solved to obtain a mass flux of oxygen entering the groundwater. This mass flux of oxygen results from the passive diffusion of oxygen from the ground surface. Using the computed mass flux, the diffusive recharge option in the BIOPLUME II fate and transport model is used to introduce the oxygen to the contaminant plume. This method was tested on a hypothetical plume and using field data from Hill AFB. The oxygen supplied by the diffusive recharge had an effect on the biodegradation of the hypothetical plumes at all contaminant concentrations. Significant effects were observed throughout the entire 1 mg/L plume and at the perimeter of all the plumes (maximum concentrations of 2, 5, and 9 mg/L). Modeling of the field site at Hill using this method was not as successful. The lack of agreement between the modeled and observed contaminant values could be a result of the poor source definition at the site and anaerobic degradation processes that are suspected to be contributing to the degradation of the plume.
A New Assay Method for Scale Inhibitor Detection at Low Concentrations
(2014-04-23) Liu, Ya; Tomson, Mason B.; Bedient, Philip B.; Li, Qilin
Accurate detection of scale inhibitors has always been crucial to scale control in industry. However, analyzing scale inhibitors at low concentrations, especially with polymeric scale inhibitors, remains an ongoing challenge. This paper presents an assay method designed to detect all types of scale inhibitors, especially at low concentrations, and an expert program developed to guide the method. The program guides the preparation of a field brine barite solution at a fixed barite super-saturation. Scale inhibitor concentration is then measured via the method of standard additions, assuming a linear relationship between the scale inhibitor concentration and the logarithm of barite induction time. Seven different scale inhibitors, including phosphonates, carboxylates and sulfonates, were detected in two typical synthetic brines at low concentrations. In addition, this assay method has also been applied to scale inhibitor detection in actual field brines. In general, this easily-implemented method can directly detect the residual level of any scale inhibitors in field brine about 0.1 mg/L active. Emphasis in this paper is on low concentrations. Measurement of low concentration scale inhibitors not only helps to monitor scaling tendency but also effectively prevents overuse of scale inhibitors and thereby protects the environment and saves money. This is one of the few methods that can detect most scale inhibitors at such low concentrations. Field applications, strengths, and interferences are discussed using laboratory and field examples.
A new method for the real-time prediction of flood peak discharges in Brays Bayou, Houston, Texas
(1993) Fisher, Ronald Todd; Bedient, Philip B.
A new method for the prediction of maximum flood stage discharges in real time that does not rely on rainfall data has been developed for the Brays Bayou drainageway in Houston, Texas. A study of 21 historical storm discharge hydrographs revealed information contained within the rising limb of the hydrograph that could be used to predict the magnitude of the peak flow in the channel with an approximate one hour lead time. A correlation has been observed between the flow that occurs in the channel at a time following the time of slope inflection on the rising limb of the hydrograph and the peak flow. A HEC-1 model has been calibrated to the watershed using two recently occurring storms. This model was used to substantiate the observed correlation through simulated hydrographs using 264 hypothetical rainfall scenarios.
A numerical model of processes governing groundwater contaminant transport
(1983) Springer, Nina K.; Bedient, Philip B.; Wheeler, Mary F.; Tomson, Mason B.
The purpose of this research was to develop a numerical model to simulate transport of solutes in groundwater which could be used to 1) predict existing or potential groundwater contamination and 2) aid determination of governing transport mechanisms in the field. The numerical model developed successfully uses a Laplace Modified Alternating Direction Implicit solution scheme to solve, for the first time in this application, a finite-difference expression for the governing transport equations. The model incorporates transport processes of advection, dilution, physical dispersion, reaction, and adsorption. The major advantages of the model are its non-iterative solution scheme which allows quick solutions, its non-time-dependent stability, and its wide and flexible range of transport process simulation capabilities. The transport model was linked to an existing groundwater flow model, GWSIM-II. This model, a modification of the Prickett-Lonnquist model used by the Texas Department of Water Resources, calculates groundwater heads over time by solving a finite difference form of the unsteady state pressure equation. The resulting combined model was called MPACTS; a model of physical and chemical transport in the subsurface. The accuracy of the model was verified by comparing MPACTS solutions and analytical solutions to simple problems. The model solutions to these problems are quite accurate when reasonable model parameters are used. In order to demonstrate application of the model to field data, MPACTS was used to simulate groundwater contamination at a rapid soil infiltration sewage treatment facility at Fort Devens, Massachusetts. Contamination by chlorides and a trace level organic, tetrachloroethylene, was modeled. The site was fairly well documented with respect to groundwater heads and chloride concentration in the immediate vicinity of the basins, but was not defined elsewhere. The lack of good definition over the whole modeled area, typical of field studies, was reflected in inaccuracies in simulated contaminant concentrations. However, the simulations were sufficiently accurate to be used for estimation of contaminant contours at the site.
A statistical investigation of ozone exposure assessment by direct and indirect measurement
(1998) Hopkins, Loren Palmer; Bedient, Philip B.
Recent studies have proposed the application of exposure-based criteria in developing alternative primary ambient ozone standards. Historically, epidemiological studies of ozone have approached exposure assessment in a simplistic fashion with simplistic methods used to estimate ambient ozone concentrations in exposure assessment. A new method for assessing human exposure to ozone has been developed. The research uses a spatial temporal statistical method, kriging, in conjunction with subject activity logs to estimate personal exposure to ozone. The personal ozone exposure to human subjects was monitored using Harvard passive samplers during August and September of 1997. Each subject logged their location and activity during the exposure period. A three-dimensional kriging model of ozone was developed to estimate the ozone exposure for each subject from ambient fixed site monitoring data. The ozone predications from the model were combined with the activity and location information, adjusted for indoor environment when applicable, to estimate personal exposure concentrations for each subject. Using two independent approaches, the kriging model was proven to provide accurate spatial and temporal estimates of ozone at subject exposure points. The results from this work show that the method developed to estimate exposure through kriging over (x,y,t) to predict ozone concentrations at exposure points combined with subject activity and location logs produces exposure estimates within the error bounds of the analytical methods for personal monitoring.
A Study of Surface Treatments on Carbonate Core Material for Application to Mineral Precipitation and Dissolution during Geologic Carbon Storage
(2013-06-05) Work, Sarah; Tomson, Mason B.; Bedient, Philip B.; Ward, C. H.; Hirasaki, George J.
Underground injection of acid gas has been studied for several decades for oil field applications, such as enhanced oil recovery (EOR), but is now being studied as a solution to climate change. This research aims to simulate underground conditions at injection sites, such as the pilot scale injection site located near the site of a coal fired power facility in the Black Warrior Basin of Alabama. This proposed carbon capture and sequestration (CCS) location would involve injection of liquid CO2 into a carbonaceous saline aquifer. The objective of this study was to investigate carbonate surface treatments that alter the kinetics and mechanism of mineral dissolution resulting from the injection of an acid gas (CO2) into a geologic formation. A variety of mineral coatings were tested in an attempt to preserve mineral integrity under acidic conditions. Surface active chemicals were first tested, including scale inhibitors, followed by a novel acid induced surface treatment that precipitates an inorganic layer on the calcite to preserve the acid soluble mineral. These experiments are the first to investigate the use of scale inhibitors for mineral preservation, although were found ultimately to have little impact on dissolution kinetics. However, anions of moderate to strong acids induced surface coatings that were determined to effectively inhibit dissolution. Additionally, a novel, high pressure flow-through experimental apparatus was developed to simulate pressure and temperature conditions relevant to injection sites. Similar mineralogical studies in the literature have used pressurized, unstirred, batch systems to simulate mineral interactions. Solids with an acid induced surface coating were tested in the high pressure column and no calcium was found to leave the column.
A transient methodology for evaluating risk reduction associated with ground water remediation at leaking underground storage tank sites
(1995) Evans, Karen L.; Bedient, Philip B.
A methodology to determine risk as a function of time varying concentration was developed and applied to three leaking underground storage tank sites for five remediation scenarios, to demonstrate the risk reduction associated with corrective actions and the transient nature of risk. The conventional method for calculating risk-based clean-up levels employs a steady-state approximation such that the receptor is assumed to be exposed to a constant concentration for the entire exposure duration. Analysis by the transient method suggests that regulated clean-up levels are conservative, and that clean-up levels derived using the conventional risk-based approach were arbitrary and highly subjective with respect to the definition of 'acceptable' risk. When compared to results from the transient analysis, the clean-up levels determined from the conventional steady-state approach were shown to be conservative by as much as an order of magnitude.
A utility approach to water resource planning
(1979) Marin, Carlos Mariano; Bedient, Philip B.
The emergence of a multiple objective philosophy in current water resources planning has provided the motivation for the relevant investment and allocation considerations. The applications, however, have been limited. The difficulties encountered have provided the impetus for the study of the feasible application of other techniques. An approach to handle the generation of alternatives within the Water Resource Council's "principles and standards" is presented. Couched within the context of multiattribute utility theory, the methodology incorporates the preferences of interest groups in guaranteeing a Paretian efficient set of alternatives. By focusing on the areas of conflict and providing a range of alternatives that exploit the points of advantage for each interest group, an explicit consideration of the tradeoffs in both a technical and political level can be effected. The results of the application of the approach to a quasi-hypothetical flood control problem are reported.
Advanced floodplain mapping of a Rio Grande Valley resaca using LIDAR and a distributed hydrologic model
(2005) Whitko, Annemarie N.; Bedient, Philip B.
The availability of high-resolution LIDAR and GIS data combined with the onset of more powerful computers has made the use of distributed parameter hydrologic models more feasible. This study employs one such model, Vflo(TM), along with a widely used hydraulic model, HEC-RAS, to simulate the runoff-response of a resaca network in Brownsville, TX using newly available LIDAR data. While previous studies have attempted to simulate the runoff-response of a resaca, they were greatly limited by the lack of detailed topographic data and information describing the hydraulic structures that connect one resaca pool to the next. Floodplain mapping in the area revealed that very little flooding occurs in and around the resacas compared to the two main drainage ditches in the area. Furthermore an evaluation of the available storage in the resacas shows great potential for the use of resacas as detention reservoirs in the future for excess stormwater.
Advanced methods for improving the lead-time and accuracy of a flood alert system in an urban watershed
(2005) Benavides, Jude Anthony; Bedient, Philip B.
The lead-time and accuracy of a flood alert system designed for a quickly responding urban watershed have been improved by incorporating a variety of new tools and methodologies. These include: the use of computer-mediated voice and data communication systems such as the Internet, high-quality hydrologic data including radar rainfall, real-time hydrologic models, assessment and use of a Quantitative Precipitation Forecast (QPF) algorithm, and the development of improved flood notification levels---providing earlier and more accurate warnings to critical institutions and emergency personnel in flood-prone areas throughout the watershed. While the research focused on one watershed in an urban setting (Brays Bayou in Houston, Texas), the results found are applicable across a broad spectrum of watershed types, provided that the need for more timely and accurate flood forecasts exists. System lead-time improvements were accomplished through the implementation and evaluation of a QPF algorithm increasingly used for short-term weather prediction across the United States. The Brays Bayou watershed provided an excellent test-bed for the collection and evaluation of QPF data. Algorithm accuracy and effectiveness were evaluated at various forecast times and basin sizes commonly found in urban watersheds. Generalized results of these analyses are presented. System accuracy improvements were accomplished with improved radar-rainfall data input and the development of real-time hydrologic models. A real-time interface for the industry standard HEC-1 hydrologic model was created, allowing the hydrologic predictions developed by this model to take greater advantage of the spatial and temporal distribution of real-time radar-rainfall data. The successful implementation of this real-time hydrologic model at the scale of Brays Bayou also provided significant lead-time improvements by providing estimates to when peak flows would actually occur. A successful validation and operational test of the entire system occurred during the November 17th, 2003 storm event. This storm event is utilized as a case study, with results illustrating wide-ranging improvements.
An assessment of point and nonpoint pollution loads into Lake Houston
(1981) Newell, Charles J.; Bedient, Philip B.; Rowe, Peter G.; Tomson, Mason B.
The urbanization process has affected the characteristics of pollutant loads from both stormwater runoff (or nonpoint sources) and from sewage treatment plants (or point sources) in the tributaties of the 2828 mi lake Houston watershed. Land use projections indicate the urban development, which has caused water quality deterioration in seme tributaties, will continue at nearly the same overall rate in the 198 to 199 period as in the 197 to 198 period. The patterns of growth, however, will shift from development concentrated in the Cypress Creek and Lake Environs areas to several of the previously undeveloped watersheds; this will impact on water quality of the streams in these areas. A detailed point source analysis indicated that most of the larger sewage treatment plants acconmodating the increases in population in the Cypress Creek watershed had difficulty in providing accepted levels of treatment. All violated State of Texas standards for effluent quality to some degree, and treatment process upsets greatly increased effluent loads for sane parameters. The fate of the plant's nutrient loads at low flow was also examined: almost all of the nutrients were carried to the lake by the Cypress Creek low flow transport process. During these low flow periods, critical for lake water quality, point sources accounted for 25% of the nitrate-nitrogen (NOg) and 75% of the total phosphorus (TP) loads to Lake Houston. The nonpoint source analysis showed that urban development has increased total suspended solids (TSS) loads to lake Efouston. The rapidly urbanizing watershed, Cypress Creek, contributes 27-35% of the annual TSS load to the lake although it accounts for only 11% of the entire basin's area. The load analysis provided the following yearly pollutant loads to the lake (for an average year's flow under present development conditions): 159 • 16Kg TSS/y ear,31.8 * 1° Kg N^NO^/year, and 1.4 • 1 Kg TP/year. Because of continuing development in the entire basin, lake TSS loads are expected to rise to 194 • 1 Kg TSS/year in 199, a 22% increase. Two different basin-wide management policies were examined and results indicated that although stormwater detention sedimentation ponds were an effective measure to prevent this increase in TSS loads, they probably could not be applied to reduce TSS loads much below present levels. The instantaneous load-runoff methodology using periodic grab sample data, used to calculate nonpoint pollutant loads, seemed to work well for TSS loads in general and for nutrient loads in the undeveloped watersheds. The method seemed to underestimate nonpoint nutient loads from developing watersheds, probably because of the high variability of stormwater runoff concentrations in these areas. An intensive storm sampling program on two storms, used in the management policy analysis, was also applied to the load-runoff methodology. This analysis indicated that future studies designing monitoring programs to calculate annual pollutant budgets to Lake Kbuston should employ intensive storm sampling techniques rather than the sampling at regular intervals performed by earlier studies.
Analysis and Prediction of Rainfall and Storm Surge Interactions in the Clear Creek Watershed using Unsteady-State HEC-RAS Hydraulic Modeling
(2012-09-05) Winter, Heather; Bedient, Philip B.; Griffin, Robert J.; Raun, Loren H.
This study presents an unsteady-state hydraulic model analysis of hurricane storm surge and rainfall-runoff interactions in the Clear Creek Watershed, a basin draining into Galveston Bay and vulnerable to flooding from both intense local rainfalls and storm surge. Storm surge and rainfall-runoff have historically been modeled separately, and thus the linkage and interactions between the two during a hurricane are not completely understood. This study simulates the two processes simultaneously by using storm surge stage hydrographs as boundary conditions in the Hydrologic Engineering Center’s – River Analysis System (HEC-RAS) hydraulic model. Storm surge hydrographs for a severe hurricane were generated in the Advanced Circulation Model for Oceanic, Coastal, and Estuarine Waters (ADCIRC) model to predict the flooding that could be caused by a worst-case scenario. Using this scenario, zones have been identified to represent areas in the Clear Creek Watershed vulnerable to flooding from storm surge, rainfall, or both.
Analysis of groundwater mounding using a surface impoundment database and Monte Carlo simulation
(1992) Rayburn, Traci Dee; Bedient, Philip B.
A database for surface impoundments (SIs) consisting of hydrogeologic and operational parameters was developed and statistically analyzed. The database was used to evaluate infiltration, groundwater mounding, contaminant transport (dilution), and the relationships between each of these mechanisms. Analytical, numerical, and statistical solutions were used for the evaluation. Hydraulic heads calculated with Hantush's analytical solution for mound growth compared well to those computed by a two-dimensional numerical transport model for unconfined aquifers (UNMOC). Infiltration from the "typical" surface impoundment (defined by the database) was modeled with UNMOC. Dilution effects were quantified and compared to those predicted by the one-dimensional Monte Carlo model (EPACML) used by EPA in specifying acceptable waste concentrations for disposal. The SI-specific database in conjunction with UNMOC predicted much less dilution than EPACML and provide an alternative approach to regulating surface impoundments.
Application of BIOPLUME II to simulate biodegradation: A study of an aviation fuel spill from a leaking underground storage tank in Traverse City, Michigan (Groundwater contamination)
(1989) Miller, Karen Michelle; Bedient, Philip B.
BIOPLUME II is a two-dimensional ground water transport model that incorporates decay terms to simulate biodegradation of organic compounds. First, the ground water data was studied, and trends in the contaminant concentrations of the indicator compounds benzene, toluene, and total xylenes (BTX) were determined to be influenced by precipitation, ground water and Lake Michigan elevations, and also interdiction field withdrawals. The model was applied to the Traverse City field site at which a leaking aviation fuel tank had contaminated the ground water. BIOPLUME II was able to calibrate the site conditions as well as the standard USGS transport code. Mass loss calculations were performed to verify the model. Over time, the contaminant source area has shrunk, and this fact was incorporated into the model to simulate field conditions after two years of the interdiction field remediating the plume. Various cleanup strategies were then compared to the existing interdiction field in terms of remediation time required.
Application of nanoparticles in downhole detection
(2014-12-11) Wang, Lu; Tomson, Mason B.; Bedient, Philip B.; Tour, James M.
The revolution of nanotechnology leads to the increasing application of nanoparticles in many industry fields. Nanoparticles, due to the small size, are supposed to transport through subsurface formation without breaking rock structure and thus have received tremendous attention1-12. Nanoparticles also have many unique physical, chemical and optical properties, which are not found in bulk samples with the same chemical composition. Such nanoparticles, therefore, may be attractive as candidates to detect the chemical and physical properties underground, by directly interact with the important targets. Because of the increasing energy demands, it becomes more desirable to develop new technology to detect the downhole conditions. In this paper, nanoparticles possessing functionalized carbon black cores and treated polyvinyl alcohol addends was designed as carrier to deliver probe molecules into the reservoir. When applied in the aqueous environment, nanoparticles tend to interact with the rock surface, which may affect the mobility and stability of the nanoparticles. Deposition of nanoparticles will remove the nanoparticles from the aqueous environment, and therefore understanding the fate and transport of nanoparticles is vitally important for determination of further application strategy. The stability and transport behavior were tested under high temperature, high salinity conditions through a variety of rock formations. A non-radioactive probe molecule, which can be easily detected by mass spectrometry, triphenolamine (TPA), was attached to the nanoparticles surface. When the nanoparticles passed through columns packing with different oil saturation ground rocks, the probe molecules, THA, was selectively released from nanoparticles. This study simulates detection and quantitative analysis of the hydrocarbon content in downhole rock formations, which is vitally needed for oilfield. This technology also shows the potential to be used for DNAPL detection in ground water remediation field. Crude oil is classified as “sour” when it contains total sulfur content greater than 0.5%. Among these sulfur species, H2S is the one of main impurities in sour crude. The sour crude is toxic and corrosive to the materials of construction in pipelines and other holding and transportation vessels. Since the sulfur amount in a sample of crude depends on where it was found, if the concentration of the sulfur species in the subsurface could be accurately monitored, then geologists might be able to evaluate the quality of the crude before large scale extraction ensues. A H2S-sensitive molecule was selected to be attached to nanoparticles surface and the detection ability of H2S concentration was tested. The experimental results show that the fluorescent enhancement of the H2S-sensitive addends correlates to the H2S content.

Browsing by Author "Bedient, Philip B."

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