VTechWorks Repository :: Browsing by Author "Younos, Tamim"

Browsing by Author "Younos, Tamim"

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The Adoption of Low Impact Development by Local Governments
Jeong, Moonsun (Virginia Tech, 2010-03-25)
Low impact development (LID) is an innovative stormwater management technique that was introduced in early 1990s. However, the transition to use of this more sustainable method has been slow due to technical, institutional, and regulatory barriers to LID adoption. The research questions for this study are: What constitutes LID adoption? Why do localities adopt LID? What are the major factors that influenced the level of LID adoption by local governments? Specifically, this study focused on motivations and key determinants of LID adoption by local governments. By answering these questions, we will have better knowledge about how to approach the adoption process of environmental innovations. The findings of the study will benefit any potential localities considering LID adoption. The theory of diffusion of innovations is applied as it is very flexible to investigate complex topics like environmental innovation involving multiple factors and environments. To explore the role of local governments in LID adoption, sub-theories like organizational innovation and policy adoption are reviewed. Based on these theoretical foundations, four constructs of variables which include innovation, organizations, motivations, and surrounding organizational context are investigated. The case study method is used for eight counties (Amherst, Bedford, Chesterfield, Fairfax, Isle of Wight, Roanoke, Stafford, and Spotsylvania) and two cities (City of Charlottesville, City of Roanoke) in Virginia. Key informants from each locality were selected for in-depth interviews and additional document reviews for each case are used to support multiple case studies. LID adoption consists of various forms such as regulations, practices, and plans. A combination of all forms of LID activities and programs was used to measure LID adoption level. Based on nine criteria (i.e., adoption mode, use of the term "LID" in local codes, code details, LID manuals, demonstration projects, number of LID projects after LID code adoption, education programs, task force, and incentives), localities with three levels of LID adoption have been determined. Influencing factors of innovation adoption varied depending on level of LID adoption (high, moderate, and low). Therefore, strategies to promote environmental innovation should be developed in relation to the level of innovation adoption. The research findings revealed two major determinants that influenced the level of LID adoption. One is strong champions, and the other is regulatory mandates. A champion-driven LID adoption model is found in high level LID adoption localities. Usually, individuals from local governments, NGOs, and development communities have played a critical role in LID adoption process. The local government organizations in this group are usually self-motivated for innovation adoption. Especially, the presence of strong champions was identified as a key factor to the higher level of innovation adoption. On the other hand, a regulation-driven LID adoption model is found in moderate to low level LID adoption localities. These localities are strongly influenced by state regulatory mandates. In these cases, external forces motivate local governments to adopt innovations.
Analysis of Sinkhole Susceptibility and Karst Distribution in the Northern Shenandoah Valley, Virginia: Implications for Low Impact Development (LID) Site Suitability Models
Hyland, Sara Elizabeth (Virginia Tech, 2005-05-13)
Increased stormwater runoff due to urban development in the northern Shenandoah Valley (NSV) region of Virginia has prompted local officials and representatives to consider Low Impact Development (LID) as a stormwater management technique. LID is based on infiltrating stormwater runoff at the source through practices such as bioretention, rain gardens, and grass swales. The karst terrain that underlies the Shenandoah Valley presents a major barrier to the use of LID. Infiltration of surface runoff in karst landscapes may threaten groundwater quality and the stability of the bedrock. In 2004 the Center for Geospatial Information Technology (CGIT) at Virginia Tech developed an LID site suitability model for the NSV region incorporating karst as a key component in distinguishing unsuitable from suitable conditions for LID. But, due to the difficulty of mapping karst, the karst layer used in the site suitability model is very coarse in resolution, based primarily on carbonate versus non-carbonate rock. This study uses a 1:24,000 scale sinkhole map derived from sinkhole boundaries identified by geologist David Hubbard (1984) of the Virginia Department of Mines and Minerals (DMME) to develop a more detailed karst map for a sub-watershed of the NSV region. The analysis uses geospatial techniques to determine the relationship between sinkhole distribution and four major landscape factors: bedrock type, soil depth to bedrock, proximity to geologic faults, and proximity to surface streams. The analysis identified three major trends in sinkhole occurrence: (1) sinkholes are more abundant in relatively pure carbonate rocks of Ordivician age; (2) sinkhole occurrence increases with proximity to fault lines; and (3) sinkholes are sparse near streams, most abundant 600 to 1400 feet away from surface streams. Based on these findings a sinkhole susceptibility index was produced using weighted overlay analysis in ArcGIS. The sinkhole susceptibility index provides a more detailed karst layer for the LID site suitability maps and can be used by the NSV region as a predictive tool for future sinkhole occurrence.
An Assessment and Modeling of Copper Plumbing pipe Failures due to Pinhole Leaks
Farooqi, Owais Ehtisham (Virginia Tech, 2006-05-19)
Pinhole leaks in copper plumbing pipes are a big concern for the homeowners. The problem is spread across the nation and remains a threat to plumbing systems of all ages. Due to the absence of a single acceptable mechanistic theory no preventive measure is available to date. Most of the present mechanistic theories are based on analysis of failed pipe samples however an objective comparison with other pipes that did not fail is seldom made. The variability in hydraulic and water quality parameters has made the problem complex and unquantifiable in terms of plumbing susceptibility to pinhole leaks. The present work determines the spatial and temporal spread of pinhole leaks across United States. The hotspot communities are identified based on repair histories and surveys. An assessment of variability in water quality is presented based on nationwide water quality data. A synthesis of causal factors is presented and a scoring system for copper pitting is developed using goal programming. A probabilistic model is presented to evaluate optimal replacement time for plumbing systems. Methodologies for mechanistic modeling based on corrosion thermodynamics and kinetics are presented.
Characterization of palmer drought index as a precursor for drought mitigation
Lohani, Vinod K. (Virginia Tech, 1995-08-15)
Coping with droughts involves two phases. In the first phase drought susceptibility of a region should be assessed for developing proper additional sources of supply which will be exploited during the course of a drought. The second phase focuses on the issuance of drought warnings and exercising mitigation measures during a drought . These kinds of information are extremely valuable to decision making authorities. In this dissertation three broad schemes i) time series modeling, ii) Markov chain analysis, and iii) dynamical systems approach are put forward for computing the drought parameters necessary for understanding the scope of the drought. These parameters include drought occurrence probabilities, duration of various drought severity classes which describe a region's drought susceptibility, and first times of arrival for non drought classes which signify times of relief for a drought-affected region. These schemes also predict drought based on given current conditions. In the time series analysis two classes of models; the fixed parameter and the time varying models are formulated. To overcome the bimodal behavior of the Pallner Drought Severity Index (PDSI), primarily due to the backtracking scheme to reset the temporary index values as the PDSI values, the models are fitted to the Z index in addition to the PDSI for the forecasting of the PDSI.
Cooperative Infrastructures for Small Water Systems: A Case Study
Young, Micki Melinda (Virginia Tech, 2002-04-04)
This case study analyzes the opportunities and potential for a cooperative structure in rural small water systems (SWS) located in Carroll County, Virginia. It is hypothesized that, by organizing as a cooperative, SWS in Virginia can obtain operational efficiency and meet the National Primary Drinking Water Standards (NPDWS) through economies of scale. Specifically, the research involves a market analysis of the factors which influence costs, operational efficiency, revenue, the exchange of technical information, operational capacities, and, thereby, the number of NPDWS violations in those participating SWS. The results of this research reveal ways in which a cooperative structure could result in efficiency and compliance gains. Results are used to develop guidelines for a conceptual cooperative structure that can be applied to SWS across rural Virginia and perhaps may have application on a broader economic and geographic scale.
Decision Support Tool for Optimal Replacement of Plumbing Systems
Lee, Juneseok (Virginia Tech, 2004-12-10)
Pinhole corrosion leak in home plumbing has emerged as a significant issue. In the major water distribution system managed by municipalities and water utilities the costs are distributed among all subscribers. The home plumbing repair/replacement cost and possible water damage cost must be addressed by the home owner. There are also issues of the value of home, insurance rates, health consequences, and taste and odor problems. These issues have become major concerns to home owners. Cradle to grave life cycle assessment is becoming an integral part of industrial manufacturing. In this thesis comprehensive details pertaining to life cycle assessment are presented. Copper tubing for plumbing installations is mainly obtained from recycled copper. Various stages of copper plumbing pipe manufacturing are explained. A comprehensive synthesis of various corrosion mechanisms is presented. Particular reference is given to copper plumbing pipe corrosion. A decision support tool for replacing copper plumbing pipes is presented. The deterioration process is grouped into early, normal and late stages. Because available data reflects late stage process, an optimization, neural network and curve fitting models are developed to infer early and normal stage behavior of the plumbing system. Utilizing the inferred leak rates a non-homogeneous poisson process model is developed to generate leak arrival times. An economically sustainable replacement criterion is adopted to determine optimal replacement time.
Design Principles and Case Study Analysis for Low Impact Development Practices - Green Roofs, Rainwater Harvesting and Vegetated Swales
Ramesh, Shalini (Virginia Tech, 2011-08-11)
This thesis on Low Impact Development (LID) Practices provides design guidelines and principles for three important LID practices: green roofs, rainwater harvesting and bioswales. The most important component of the thesis is the qualitative analysis of various case studies based on the LID objectives drawn from the literature review for each LID practice. Through the course of my research, I found that there was no one single source which provided information on the design guidelines accompanied by case examples which could help the designer with built examples where the LID practices have been executed. Therefore, developing this thesis document which provided all this information started as my masters thesis project. The document is designed to be used by people with a variety of expertise like landscape architects, landscape contractors, engineers and clients. The manual is organized into five chapters. The manual details the process of stormwater management and then gradually leads to the evolution of Low Impact Development Practices and detailing out three important LID practices: green roofs, rainwater harvesting, vegetated swales and briefly about infiltration systems. The LID principles outlined in this manual were developed over the last few years to address runoff issues associated with the new residential, commercial and industrial suburban developments. Information to develop this manual has been drawn from numerous sources like the Low Impact Design Strategies developed by the Prince George's County, Maryland, US EPA, Low Impact Development urban design tools and numerous other research papers. It is my hope that the manual will provide adequate information to its users by not only providing design guidelines but also provide built examples through the case studies.
Determining Sources of Fecal Pollution in Washington D.C. Waterways
Porter, Kimberly Rae (Virginia Tech, 2003-11-19)
Antibiotic resistance analysis (ARA) of Enterococci was used to determine sources of fecal contamination in three District of Columbia waterways: Rock Creek, the Anacostia River, and the Potomac River. These three waterways were identified as exceeding water quality standards set for fecal coliform levels and were designated by the District of Columbia to the Environmental Protection Agency's 303 (d) impaired waters list. A library profile of 1,806 enterococcus isolates from known sources was built based on antibiotic resistance patterns from thirty concentrations of nine antibiotics. These sources included human, cattle, chicken, horse, goat, sheep, deer, raccoon, muskrat, goose, seagull, coyote, duck, wild turkey, dog, and cat. Antibiotic profiles were characterized for 24 unknown enterococci isolates on each of 198 samples (38 samples from the Potomac River, 79 samples from the Anacostia River, and 81 samples from Rock Creek) collected periodically from July 2002 through April 2003. Two major storm events were also sampled during this period. These isolate profiles were compared to the known source library using logistic regression. Three dominant sources of fecal pollution were detected in the Potomac River: livestock (30%), human (29%), and wildlife (22%). Three dominant signatures were also detected in Rock Creek: horse (26%), human (26%), and wildlife (24%). Human was the only dominant source detected in the Anacostia River, averaging 43% over the sampling period. The results of this study indicate that human is a substantial contributor to the fecal contamination problems, especially in the Anacostia River, but there are significant agricultural and wildlife contributions as well. Significant and predictable seasonal variations were also detected, indicating the influence of precipitation on source distributions. The results of this study will aid the Metropolitan Washington D.C. Council of Governments in making important management decisions to help improve the water quality in and around the Washington D.C. area. Expanding the limits of ARA was also an integral part of this research. Three new and even controversial analytical techniques were run on the data collected from this project in an attempt to improve confidence and provide direction to the results of this study. The first was a comparison of the more commonly used statistical analysis model discriminate analysis (DA) with logistic regression (LR). No significant difference was found between the output of the two models for the known source libraries, therefore no suggestion could be made in favor of one model over the other. Another analytical test of the data was the introduction of a standard requiring isolates to meet a minimum of 80% similarity to the known source profiles where it was classified. With the 80% cutoff, between 41% and 44% of the isolates could not be classified to any source and were placed in an unknown category. Based on the remaining isolates, source distributions were recalculated and were not statistically different than those calculated with no restriction for isolate similarity for matching. The last major test of the data was the analysis of the library for representativeness via pulled sample cross validation and the exclusion of all duplicate patterns from the known source library. These analyses did not confirm the representativeness of the databases, but results were further analyzed based on the implications these analyses have on library based methods.
Determining the Sustainability of Coal Mine Cavity Discharge as a Drinking Water Source
Anderson, Eric T. (Virginia Tech, 1999-03-30)
In southwestern Virginia, adequate sources of public water for small isolated communities are difficult to find. While many alternatives exist, one of the largest sources of water in this region is flooded abandoned coal mines. One such coal mine aquifer was chosen for a sustainability study in Dickenson County, Virginia. A flowrate monitoring system was installed at the point of discharge from the mine, and the flow records from three months of data collection were analyzed. The recording period included one of the driest periods in recent years, and the flowrate data recorded provided useful information regarding the sustainability of the system. After a study of the geology and groundwater flow patterns in the region, it was determined that a coal mine aquifer is very similar to the extremely heterogeneous system seen in karst landscapes. Thus, techniques common to karst phenomenon were used to analyze the spring hydrograph. A spring recession analysis was performed upon five storm recessions, and the coefficients for each recession compared and discussed in light of known geologic information. It was discovered that the recession coefficients described the flow from the mine very adequately and that the mine response to a rainfall pulse was very similar to the response of certain types of karst aquifers. This information was used to predict a sustainable flow from the mine. A cross-correlation analysis was performed in an attempt to fit a "black box" model to the flow data, as well as to verify the results of the spring recession analysis. The correlation analysis proved that one rainfall event produced many separate reactions in the flowrate at the mine discharge point. This strengthened results concluded by the recession analysis. It was found that the flow record was not long enough to adequately create a statistical model, but a procedure was described that could be used to model flows once a larger flow record was available.
Developing a Service-Learning Program for Watershed Management: Lessons from the Stroubles Creek Watershed Initiative
de Leon, Raymond F. (Virginia Tech, 2002-04-22)
There has been a growing interest and support by many state and local programs to address aquatic resource protection and restoration at a watershed level. The desire by many programs to implement watershed management programs has become more than just a need, rather a necessity to ensure suitable water resources. However, many challenges arise when developing and sustaining watershed programs. One such challenge is that watershed programs are resource intensive. These programs require significant funds to support monitoring, research, effective management, and to provide public outreach. In addition, these programs require knowledgeable and skilled water resource professionals who can implement and manage these tasks. Integrating university-knowledge and resources into the watershed effort can meet many of these challenges. Faculty, students, and in-kind university support can contribute knowledge, technical support, research funds, and personnel to aid and enhance watershed management activities. Furthermore, connecting watershed management activities with academic work can foster the development of future environmental planning, policy, and science professionals. The overall goal of this paper is to explore the integration of service-learning in higher education within watershed management activities. The concepts and benefits of service-learning are explored in this paper. An example of a watershed-based, service-learning initiative in the Stroubles Creek watershed, Virginia is presented. In addition, perspectives gathered from the Initiative's students and project coordinator (the author) on their work experience as service-learners are provided. The lessons and recommendations presented in this paper pave way to means of sustaining and enhancing service-learning program in watershed activities.
Developing Digital Monitoring Protocols for Use in Volunteer Stream Assessment
Anderson, Jason (Virginia Tech, 2001-12-06)
The traditional paper-based method of field data collection has always been a time-consuming and cumbersome process. Agency personnel in the field complete a standard evaluation form, which is then returned to the office and entered into a computer database for storage and analysis. Throughout this process, data can easily be lost or misinterpreted. As data requirements continue to expand, field data collection can quickly overwhelm a regulatory agency's manpower and resources, which only serves to exacerbate these problems. Recent technological developments can help agencies and organizations keep up with this growing demand and have begun to change the method of data collection and management. The overall goal of this study is to develop, demonstrate, and evaluate a digital protocol for the use of technology in a volunteer stream monitoring application and draw conclusions on its applicability as a more effective means of data collection in a wide variety of fields. The protocol includes digital evaluation forms and integrated help files for use in the field. The digital evaluation forms are based on paper evaluation forms developed by researchers conducting a stream corridor assessment of Stroubles Creek in Blacksburg, Virginia. The protocol was developed using available hardware and software. Collected data can be downloaded directly from a Personal Digital Assistant (PDA) and stored on a hard drive or system server. The data can then be input directly into a Geographic Information System (GIS) database to enhance the visualization and usefulness of the information. The GIS allows surveyors to view the relationships among the many factors affecting the stream, as well as preparing the data for advanced analysis. Two examples are provided: a field application of the protocol on streams currently listed for Total Maximum Daily Load (TMDL) development; and an environmental education setting in a Virginia elementary school. Conclusions drawn from these applications are also described.
Effect of Spatial Scale on Hydrologic Modeling in a Headwater Catchment
Fedak, Ryan Michael (Virginia Tech, 1999-01-29)
In this study, two hydrologic models were applied to the mountainous Back Creek catchment, located in the headwaters of the Roanoke River in Southwest Virginia. The two models employed were HEC-1, an event based lumped model, and TOPMODEL, a continuous semi-distributed model. These models were used to investigate (a) the issue of spatial scale in hydrologic modeling, and (b) two approaches to modeling, continuous versus event based. Two HEC-1 models were developed with a different number of subareas in each. The hydrographs generated by each HEC-1 model for a number of large rainfall events were analyzed visually and statistically. No observable improvement resulted from increasing the number of subareas in the HEC-1 models from 20 to 81. TOPMODEL was applied to the same watershed using a series of different size grid cells. The first step in applying TOPMODEL to a watershed involves GIS analysis which results in a raster grid of elevations used for the calculation of the topographic index, ln(a/tan b). The hydrographs generated by TOPMODEL with each grid cell size were compared in order to assess the sensitivity of TOPMODEL hydrographs to grid cell size. An increase in grid cell size from 15 to 120 meters resulted in increased values of the watershed mean of the topographic index. However, hydrographs generated by TOPMODEL were completely unaffected by this increase in the topographic index. Analyses were also performed to determine the sensitivity of TOPMODEL hydrographs to several model parameters. It was determined that the parameters that had the greatest effect on hydrographs generated by TOPMODEL were the m and ln(To) parameters. The modeling performances of the event based HEC-1 and the continuous TOPMODEL were analyzed and compared visually and statistically for a number of large storms. The limited number of storms used to compare HEC-1 and TOPMODEL makes it difficult to determine definitively which model simulates large storms better. It does appear that perhaps HEC-1 is slightly superior in that regard. TOPMODEL was also executed as an event based model for two single events and the resulting hydrographs were compared to the HEC-1 and continuous TOPMODEL results. Both HEC-1 and TOPMODEL (when used as a continuous model) simulate large storms better than TOPMODEL (when used as an event based model).
An effective medium approximation and Monte Carlo simulation in subsurface flow modeling
Shrestha, Surendra Prakash (Virginia Tech, 1993)
An effective medium approximation and a refined Monte Carlo simulation procedure for solving the stochastic groundwater flow problem are presented. The effective medium approximation permits one to solve the stochastic groundwater flow problem in a single run to generate the expected pressure head field. The proposed effective hydraulic conductivity expression for the effective medium is of the same form as the local Gardner’s equation and is easy to use. The refined Monte Carlo simulation procedure uses analytical means to estimate the sample size by controlling the error incurred in using the sample average in place of its population mean at a chosen confidence level. This estimator consistently performs well. Also, a variance reducing estimator which is different from the simple average for pressure head is developed. This estimator takes advantage of the correlation between the saturated conductivity and the pressure head distribution to reduce the output variance and is unbiased. This reduced variance results in a smaller width of uncertainty about the predicted pressure head. Both the effective medium approximation and the Monte Carlo approaches perform well when applied to several problems.
An Evaluation and Pressure-Driven Design of Potable Water Plumbing Systems
Ladd, Jonathan Stuart (Virginia Tech, 2005-05-13)
Potable water distribution systems are broken into major and minor distribution networks. Major water distribution networks refer to large-scale municipal pipe systems extending from the treatment plant to the upstream node of the water service line for buildings. Minor water distribution systems, also referred to as plumbing water distribution systems, run from the upstream node of the water service line to all interior plumbing fixtures and demand nodes associated with the building. Most texts and research papers focus on major systems, while only a small number of documents are available concerning the design and analysis of minor systems. In general, the available minor system documents are quite prescriptive in nature. This thesis presents a comprehensive evaluation of contemporary plumbing water distribution system design. All underlying theory is explained and advantages and drawbacks are discussed. Furthermore, contemporary methods for designing minor distribution systems have come under recent scrutiny. Issues have been raised regarding the accuracy of water demand estimation procedures for plumbing systems, namely, Hunter's method. Demand estimates are crucial for designing minor piping systems. The formulation and application of a pressure-driven design approach to replace Hunter-based design methods is presented. EPANET, a commonly used hydraulic modeling software package, is utilized to evaluate network behavior. Example applications are presented to illustrate the robustness of a pressure-driven approach, while also allowing the evaluation of plumbing water distribution system performance under worst-case loading conditions.
Evaluation, Development and Improvement of Genotypic, Phenotypic and Chemical Microbial Source Tracking Methods and Application to Fecal Pollution at Virginia's Public Beaches
Dickerson, Jerold W. Jr. (Virginia Tech, 2008-07-29)
The microbial source tracking (MST) methods of antibiotic resistance analysis (ARA) and fluorometry (to detect optical brighteners in detergents) were used in the summers of 2004 and 2005 to determine the origins of fecal pollution at beaches with a past history of, or the potential for, high enterococci counts and posted advisories. At Hilton and Anderson beaches, ARA and fluorometry in the summer of 2004 detected substantial human-origin pollution in locations producing consistently high counts of Enterococcus spp. Investigations by municipal officials led to the fluorometric detection and subsequent repair of sewage infrastructure problems at both beaches. The success of these mitigation efforts was confirmed during the summer of 2005 using ARA and fluorometry, with the results cross-validated by pulsed-field gel electrophoresis (PFGE). Results at other beaches indicated that birds and/or wildlife were largely responsible for elevated enterococci levels during 2004 and 2005. The application of fluorometry proved difficult in opens waters due to high levels of dilution, but showed potential for use in storm drains. An additional study developed and tested a new library-based MST approach based on the pattern of DNA band lengths produced by the amplification of the 16S-23S rDNA intergenic spacer region, and subsequent digestion using the restriction endonuclease MboI. Initial results from small known-source libraries yielded high average rates of correct classification (ARCC). However, an increase in the library size was accompanied by a reduction in the ARCC of the library and the method was deemed unsuccessful, and unsuitable for field application. A final study focused on the potential for classification bias with disproportionate source category sizes using discriminant analysis (DA), logistic regression (LR), and k-nearest neighbor (K-NN) statistical classification algorithms. Findings indicated that DA was the most robust algorithm for use with source category imbalance when measuring both correct and incorrect classification rates. Conversely k-NN was identified as the most sensitive algorithm to imbalances with the greatest levels of distortion obtained from the highest k values. Conclusions of this project include: 1) application of a validation set, as well as a minimum detectable percentage to known-source libraries aids in accurately assessing the classification power of the library and reducing the false positive identification of contributing fecal sources; 2) the validation of MST results using multiple methods is recommended for field applications; 3) fluorometry displayed potential for detecting optical brighteners as indicators of sewage leaks in storm drains; 4) the digestion of the 16S-23S rDNA intergenic spacer region of Enterococcus spp. using MboI does not provided suitable discriminatory power for use as an MST method; and 5) DA was the least, and k-NN the most, sensitive algorithm to imbalances in the size of source categories in a known-source library.
A GPS-IPW Based Methodology for Forecasting Heavy Rain Events
Gorugantula, Srikanth V. L. (Virginia Tech, 2003-05-15)
The mountainous western Virginia is the source of the headwater streams for the New, the Roanoke, and the James rivers. The region is prone to flash flooding, typically the result of localized precipitation. Fortunately, within the region, there is an efficient system of instruments for real-time data gathering with IFLOWS (Integrated Flood Observing and Warning System) gages, WSR-88D Doppler radar, and high precision GPS (Global Positioning System) receiver. The focus of this research is to combine the measurements from these various sensors in an algorithmic framework to determine the flash flood magnitude. It has been found that the trend in the GPS signals serves as a precursor for rain events with a lead-time of 30 minutes to 2 hours. The methodology proposed herein takes advantage of this lead-time as the trigger to initiate alert related calculations. It is shown here that the sum of the rates of change of total cloud water, water vapor contents and logarithmic profiles of partial pressure of dry air and temperature in an atmospheric column is equal to the rain rate. The total water content is measurable as the profiles of integrated precipitable water (IPW) from the GPS, the vertically integrated liquid (VIL) from the radar (representing different phases of the atmospheric water) and the pressure and temperature profiles are available. An example problem is presented illustrating the involving the calculations.
Hydrogeology and Simulated Water Budget of the Rio Cobre and Rio Minho-Milk River Basins, Jamaica, West Indies
Wishart, DeBonne Natalie (Virginia Tech, 2000-09-20)
An investigation was undertaken to better understand the hydrogeologic framework of the Rio Cobre and Rio Minho-Milk river basins, Jamaica, West Indies. A quasi three-dimensional finite-difference groundwater flow model was used to conceptualize flow conditions and establish a hydrogeologic budget of the region. The Rio Cobre and Rio Minho-Milk river basins lie on the Clarendon Block, an area with a complex geologic history. The geologic history includes: 1) the intrusion of calc-alkaline granites, 2) morphotectonic sedimentation, 3) three episodes of deformation by transpressional and transcurrent tectonics, 4) the deposition of a highly permeable, Tertiary carbonate platform, and 5) the development of near surface karst oriented with the major NNW-SSE fault trend in the basins. Since deposition, compression, faulting, and solution have modified the distribution and thickness of carbonate rocks impacting the ground-water flow of the region. The most notable features are the older NNW-SSE trend dip-slip faults and the younger E-W trend strike-slip faults, notably the South Coast Fault (SCF) formed during the Laramide Orogeny. The White Limestone aquifer is the principal aquifer of the Rio Cobre and Rio Minho-Milk river basins in the parishes of St. Catherine, Clarendon, and partly in Manchester. It is characterized by intercalated sequences of permeable rubbly and micritic carbonate rocks. The age of the rocks range from Late Cretaceous (Maastrichtian) to Recent. The permeability of the South Coast fault and the high hydraulic conductivity value associated with the Tertiary carbonate platform (480 m/d) in the Lower Rio Minho-Milk River basin control the gradient of the potentiometric surface and ground water flow in that region The agreement between the measured and the simulated hydraulic heads obtained for this steady-state model suggests that the values assigned to the hydraulic properties that characterize the ground-water flow of the White Limestone aquifer are reasonable. Recharge to the area occurs as net recharge in addition to upland subsurface inflow across the general head boundary in the northern part of the study area. Comparisons of calculated and observed values of head indicate that simulated groundwater flow field generally agree with field conditions. Several simplifying assumptions were made for the conceptualization and simulation of flow in the basins: 1) during the 1998 water year, ground-water in the basins was considered at steady-state, 2) pumping does not significantly affect the level of hydraulic heads; therefore pumping wells are not simulated, 3) Net recharge from precipitation varies spatially, 4) karstification and aquifer heterogeneity impact on the distribution of hydraulic conductivity, 5) Darcy's law is applicable to flow through the fractures and solutions openings in a karst region, 6) flow in the White Limestone aquifer occurs in the uppermost 650 m and vertical flow is assumed to be controlled by intervening units, 7) evaporation was not explicitly simulated in the model. Recharge rates were considered as "net recharge," and 8) submarine discharge occurs from the aquifer along the coast where aquifers are hydraulically connected to the sea. Ground-water flow in the basins was conceptualized as a quasi three-dimensional flow system in which two model layers were used. The model boundaries selected to represent natural hydrologic boundaries include (1) a no-flow along the western and eastern boundaries, (2) a constant head boundary along the freshwater/saltwater interface; (3) a general head boundary along the northern boundary; and (4) a horizontal-flow barrier boundary along the South Coast Fault; and (5) river leakage boundaries along major rivers draining the coastal basins. The simulated region is an area of 2,550 square kilometers, two-thirds of which is hilly and the remainder, irrigated plains with small swamps draining the area. The model consists of over 337,500 cells and employed a regular grid spacing of 200m x 160m. The model was designed and calibrated to steady-state conditions from data observed/estimated during water year 1998. The Water Resources Authority of Jamaica (WRAJ) will use the results of the modeling study as a predictive tool for long-term management and monitoring of water resources in the region. The model was calibrated using a manual trial-and-error adjustment of parameters. Hydraulic conductivity values in both model layers, hydraulic conductivity at the general-head boundary, and streambed conductance were adjusted during successive simulations until computed head values approximated field conditions. The computed potentiometric surface is an adequate or reasonable match on a regional scale, with the general horizontal hydraulic gradient oriented with the main fault trend NNW-SSE in both basins. Sensitivity tests of the calibrated model were conducted on net recharge, hydraulic conductivity, hydraulic conductivity assigned along the general-head boundary, and streambed vertical conductance to determine if differences between simulated and observed values were similar to the range of uncertainty in the values of input data and boundary conditions. Based on the results obtained from the sensitivity analysis, it is apparent that the model is extremely sensitive to changes in horizontal hydraulic conductivity and recharge in the form of precipitation. The model is least sensitive to streambed vertical hydraulic conductivity.
Linear Power Discretization and Nonlinear Formulations for Optimizing Hydropower in a Pumped Storage System
Moore, Craig S. (Virginia Tech, 2003-07-18)
Operation of a pumped storage system is dictated by the time dependent price of electricity and capacity limitations of the generating plants. This thesis considers the optimization of the Smith Mountain Lake-Leesville Pumped Storage-Hydroelectric facility. The constraints include the upper and lower reservoir capacities, downstream channel capacity and flood stage, in-stream flow needs, efficiency and capacity of the generating and pumping units, storage-release relationships, and permissible fluctuation of the upper reservoir water surface elevation to provide a recreational environment for the lake shore property owners. Two formulations are presented: (1) a nonlinear mixed integer program and (2) a discretized linear mixed integer program. These formulations optimize the operating procedure to generate maximum revenue from the facility. Both formulations are general and are applicable to any pumped storage system. The nonlinear program retains the physical aspects of the system as they are but suffers from non-convexity related issues. The linear formulation uses a discretization scheme to approximate the nonlinear efficiency, pump, turbine, spillway discharge, tailrace elevation-discharge, and storage-elevation relationships. Also, there are binary unit dispatch and either/or constraints accommodating spill and gated release. Both formulations are applied to a simplified scheme of the Smith Mountain Lake and Leesville pumped storage system. The simplified scheme uses a reduced number of generating and pumping units at the upper reservoir to accommodate the software limitations. Various sensitivity analyses were performed to test the formulations. The linear formulation consistently performs better than the nonlinear. The nonlinear solution requires a good starting point for optimization. It is most useful as a verification tool for the solution from the linear program on all occasions. The formulations yield the best schedules for generating and pumping. A coarse time interval limits the use of all pumps in the presence of the spill constraint. A sufficiently large difference in the diurnal unit price encourages short-term pump back as opposed to a weekly cycle. The Leesville (downstream) reservoir affects the power production schedule with its large (approx. 9 ft) forebay rise for every foot drop at the Smith Mountain Lake. The linear formulation provides a valuable tool for studying the system under a wide range of conditions without having to worry about the computational difficulties associated with the nonlinear formulation.
A Mechanistic Analysis Based Decision Support System for Scheduling Optimal Pipeline Replacement
Agbenowosi, Newland Komla (Virginia Tech, 2000-09-08)
Failure of pipes in water distribution systems is a common occurrence especially in large cities. The failure of a pipe results in: loss of water; property damage; interruption of service; decreased system performance; and the financial cost of restoring the failed pipe. The cost of replacement and rehabilitation in the United States is estimated at 23 plus billion dollars. It is virtually impossible to replace all vulnerable pipes at the same time. As a result, there is a need for methods that can help in progressive system rehabilitation and replacement subject to budgetary constraints. If delaying is considered a good strategy due to the time value of money then, the timing of preventive maintenance becomes a crucial element for system maintenance and operation. The central under pinning element in the decision process for scheduling preventive maintenance is the deteriorating nature of a pipe under a given surrounding. By planning to replace pipes before they fail, proper planning can be put in place for securing of finances and labor force needed to rehabilitate the pipes. With this approach, service interruptions are minimized as the loss of service time is limited to the time used in replacing the pipe. In this research, a mechanistic model for assessing the stage of deterioration of an underground pipe is developed. The developed model consists of three sub-models namely, the Pipe Load Model (PLM), the Pipe Deterioration Model (PDM), and the Pipe Break Model (PBM). The PLM simulates the loads and stresses exerted on a buried water main. These loads include the earth load, traffic load, internal pressure, expansive soil loads, thermal, and frost loads. The PDM simulates the deterioration of the pipe due to corrosion resulting from the physical characteristics of the pipe environment. The pipe deterioration effect is modeled in two stages. First, the thinning of the pipe wall is modeled using a corrosion model. Second, the localized pit growth is used to determine the residual strength of the pipe based on the fracture toughness and the initial design strength of the pipe. The PBM assesses the vulnerability of a pipe at any time in terms of a critical safety factor. The safety factor is defined as the ratio of residual strength to applied stress. For a conservative estimate the multiplier effect due to thermal and frost loads are considered. For a chosen analysis period, say 50 years, the pipes with safety factors less than the critical safety factor are selected and ordered by their rank. Aided by the prioritized list of failure prone pipes, utilities can organize a replacement schedule that minimizes cost over time. Additionally a physically based regression model for determining the optimal replacement time of pipe is also presented. A methodology for assessing the consequences of accelerated and delayed replacement is also provided. The methodologies developed in this dissertation will enable utilities to formulate future budgetary needs compatible with the intended level of service. An application of the model and results are included in the dissertation.
Optimal design of municipal and irrigation water distribution systems
Ahn, Taejin (Virginia Tech, 1993-12-07)
In two-dimensional flow, the point of flow separation from the surface coincides with the point at which the skin friction vanishes. However, in three-dimensional flow, the situation is much more complex and the flow separation is rarely associated with the vanishing of the wall shear stress except in a few special cases. Though the effects of cross-plane separation are substantial and have been recognized for some time, the phenomenon of flow separation over three-dimensional bodies is still far from being completely understood. The flow is so complex that no completely satisfactory analytical tools are available at the moment. In an attempt to logically identify the various effects and parametric dependence while simultaneously minimizing configuration dependent issue, the flow over a 6 to 1 prolate spheroid, which is a generic three-dimensional body, is investigated. For the identification of the general flow pattern and better understanding of the flow field, surface-oil-flow visualization tests and force and moment tests were performed. The angle of attack effect and Reynolds number effect on the separation location are studied with natural transition. Forces and moments tests, surface pressure distribution measurements as well as the surface pressure fluctuations, and mini-tuft flow visualization tests were made to document the flow characteristics on the surface of the body with an artificial boundary layer trip.

Browsing by Author "Younos, Tamim"

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