Category: Research Sponsored by GWRI

Principal Investigator: Fotis Sotiropoulos (Georgia Tech)

Sponsor: GWRI
Start Date: 2000-03-01; Completion Date: 2001-02-28;
Keywords: Hydrodynamic Models, Open Channel Flow, Numeric Simulation

Summary:

In this report, we develop a two-dimensional hydrodynamic model for simulating swallow-water open-channel flows using depth-averaged equations. The model is capable of handling arbitrarily shaped channel geometries such as those typically encountered in natural rivers. The time-dependent, depth-averaged equations are formulated in generalized, non-orthogonal curvilinear coordinates so that complex river reaches can be accurately modeled using body-fitted computational grids. The equations are discretized in space using a conservative second-order accurate finite-volume method. Adaptive artificial dissipation terms, with scalar and matrix-valued scaling, are explicitly introduced into the discrete equations to ensure that the resulting scheme is applicable to all flow regimes and can accurately capture hydraulic jumps. The discrete equations are integrated in time using a four-stage Runge-Kutta method. For steady-state computations the convergence of the Runge-Kutta algorithm is enhanced using local time stepping, implicit residual smoothing, and multigrid acceleration. Time accurate solutions may also be obtained by integrating the governing equations in time using the four-stage, second-order accurate in time, Runge-Kutta scheme without implementing the aforementioned convergence acceleration measures.
To validate the numerical model, we carry out calculations for a variety of open channel flows for which experimental data have been reported in the literature. The calculated test cases include flow in strongly curved channels and channel expansions. For all cases considered the numerical method is shown to yield solutions of comparable accuracy to those reported in earlier studies in the literature using depth-averaged equations. Discrepancies between predictions and experiments are observed only for very strongly curved channels for which three-dimensional effects dominate.
Due to the lack of detailed bathymetry and flow measurement data for the ACT and ACF basins, the present numerical model was not applied to a real-life reach as was initially intended. This not withstanding, however, the method has been designed to be sufficiently general and its application to a natural geometry is straightforward. The good overall agreement between measurements and numerical simulations for the test cases considered in this report suggests that the present method could serve as a powerful computational tool for understanding the complex flow patterns in the ACT and ACF basins and for guiding the development of simpler one-dimensional models.

Principal Investigator: Peter Hartel (University of Georgia)

Sponsor: GWRI
Start Date: 2000-03-01; Completion Date: 2001-02-28;
Keywords: Coliform isolation, Pollution source assessment, Pollution transport assessment, Pollutant source control

Problem and research objective:

Fecal coliforms consist of several bacterial genera from the family Enterobacteriaceae that can grow on a selective medium at 44.5°C for 24 hours. Fecal coliforms normally inhabit the intestinal tract of warm-blooded animals and their presence in soil or water is a good indicator that the soil or water was contaminated by bacterial pathogens. For example, when numbers of fecal coliforms exceed 2,000 per 100 mL of water, the likelihood of bacterial pathogens in the water is 98.1% (Geldreich, 1970). Fecal coliform counts are typically used to monitor Georgia’s recreational waters.

One of the most vexing problems in isolating fecal coliforms from water samples is not knowing the host origin of these bacteria. In the past, the only way to identify the host origin of a bacterium was to observe the bacterium’s various phenotypic markers (i.e., characteristics expressed by the bacterium, like antibiotic resistance). The main problems with using phenotypic markers are their lack of reproducibility and lack of discriminatory power (ability to distinguish two closely related strains). However, in recent years, it has become possible to identify the host origin of a bacterium based on its DNA. This alternative method, called genotyping, not only has increased reproducibility, but also has increased discriminatory power. The most common of these genotypic methods include chromosomal DNA restriction analysis, plasmid typing, pulsed field gel electrophoresis, various polymerase chain reaction (PCR) methods, and ribotyping (Farber, 1996).

Each genotypic method has its advantages and disadvantages with respect to strains that can be typed, reproducibility, discriminatory power, ease of interpretation, and ease of performance. In this report, the genotypic method selected was ribotyping. Ribotyping is based on ribosomal RNA (rRNA). Ribosomal RNA is present in all bacteria, and is composed of three species, 5S, 16S, and 23S. The DNA in the bacterium that encodes for these three species of rRNA is usually present in 2 to 11 copies and is highly conserved (does not mutate; Grimont and Grimont, 1986). In ribotyping, the DNA is isolated from the bacterium and cut with a special enzyme that only recognizes certain DNA sequences (i.e., a restriction enzyme). The DNA is electrophoresed in a gel and the DNA transferred to a nylon membrane (this is called Southern blotting). The membrane is probed with a chemiluminescent copy of the 5S, 16S, and 23S portions of the DNA and, when properly treated, the membrane gives a pattern that can be scanned with an imager. As a method for distinguishing a subspecies of a bacterium, ribotyping is considered to have excellent reproducibility, good discriminatory power, excellent ease of interpretation, and good ease of performance (Farber, 1996).

Here, the fecal coliform selected for ribotyping was Escherichia coli. This bacterium was selected for five reasons. First, as a fecal coliform, E. coli is accepted by the American Public Health Association as a good indicator of pathogenic bacteria (Clesceri et al., 1998). Second, most environmental ribotyping has been done with this bacterium. As a result, the methodology for ribotyping this bacterium is established. Third, there is good scientific evidence that specific strains of E. coli are associated with different host species (e.g., Amor et al., 2000). Fourth, E. coli does not exist as a stable population in the environment unless the source of contamination is persistent. Fifth, E. coli is easy to isolate and easy to manipulate genetically.

Principal Investigator: Carolyn Ruppel (Georgia Tech)

Sponsor: GWRI
Start Date: 1998-09-01; Completion Date: 2000-08-31;
Keywords: Groundwater, Hydrogeochemistry, Water Quality

Problem and Research Objectives:

Three undeveloped barrier islands in coastal Georgia have been mentioned as possible sites for future developments. This has led to interests by regional planners in the impact of urbanization and ecosystem destruction on the hydrologic systems beneath these barrier islands. In fact, the availability and quality of fresh water resources on barrier islands are considered key factors controlling the sustainability of natural systems and human development, as well as the continued viability of ecosystems in adjacent wetlands. The goal of this project is to develop a baseline for monitoring future development related changes in surficial acquifer systems on the concerned islands. The project is scheduled to last two years, of which the first one has now been completed. The following text presents the preliminary results of year 1. It also provides an overview of the planned work for year 2.

Principal Investigator: Todd Rasmussen (University of Georgia)

Sponsor: GWRI
Start Date: 1999-03-01; Completion Date: 2000-02-29;
Keywords: Geomorphological and Geochemical processes, Climate and Hydrologic processes, Non Point Pollution, Sediments

Problem and Research Objectives:

Sediment in streams and lakes within the Southeast adversely affects aquatic habitats and presents a substantial health hazard by reducing the clarity of water, thus reducing biologic productivity. Coarse suspended solids also bury benthic habitats, thus diminishing overall species abundance and diversity. The ecological consequences of sediments in streams have been particularly detrimental to Georgia’s native aquatic species. Additional consequences result from sediment transport. Nonpoint pollutant inputs to streams such as nutrients, metals, herbicides, insecticides, and fecal coliform are highly correlated with sediment inputs. The long term human and environmental health consequences from these non point sources are clearly a matter of local, regional, and national concern. Incomplete data limit the understanding of modern and historical sediment transport rates and inventories of Georgia Piedmont streams. A better understanding of historical and modern inputs provides the opportunity for identifying alternative management strategies for nonpoint pollution control that reduce or eliminate future environmental and health risks. The project investigated a multi-pronged approach for estimating the magnitude and distribution of suspended and bedload sediments.

Principal Investigator: Terry W. Sturm (Georgia Tech)

Sponsor: GWRI
Start Date: 1999-03-01; Completion Date: 2000-02-29;
Keywords: Climate and Hydrologic processes, Geomorphological and Geochemical processes, Sediments, Models

Problem and Research Objectives:

Continued development in urban watersheds without adequate controls on sediment production from construction activities contributes sediment load to urban streams that may affect its sediment regime. Subsequent deposition of the sediment chokes the benthic aquatic habitat, and affects storage in the channel and floodplain and thus the flooding potential of the stream. In addition, urbanization creates a greater volume of runoff and higher peak flows with a different timing than exists prior to urbanization. These higher flows may contribute to bank erosion in some stream reaches and deposition further downstream. The result is again a change in geometry and sediment regime of the natural stream with consequent adverse affects on aquatic habitat and stream water quality. Furthermore, the deposited finer-grained sediments from urbanized areas may carry with them attached contaminants that are subject of resuspension during subsequent flood conditions. While much work has been done on urban hydrology to predict changes in runoff characteristics due to urbanization, much less attention has been paid to the closely related sediment effects and the changes that they cause in flooding potential and water quality of the recieving stream over the entire watershed. The research project provides a case study of an urban stream to distinguish sediment contributions from watershed development and bank erosion, resultant changes in floodpain and channel storage, and the final effect on flood routing and thus flooding potential as well as movement of sediment-bound contaminants through the watershed system. In addition, a methodology has been developed that can be applied to other urban streams to predict the effects of urban development not just on the hydrology of the watershed, but on its sedimentology as well. As a result of the study, recommendations will be made on the relative efficacy of specific control measures such as best-management practices on contruction sites to limit sediment yield, artificially-created wetlands for aditional floodplain and sediment storage, streambank stabilization, vegetative buffer zones along the stream, and strict constols on development of the floodplain. This methodology allows decision makers to make more informed watershed-wide decisions rather than piecemeal approval and disapproval of particular development projects.

Principal Investigator: David Wenner (University of Georgia)

Sponsor: GWRI
Start Date: 1999-03-01; Completion Date: 2000-02-29;
Keywords: Groundwater Flow and Transport, Geomorphological and Geochemical processes, Groundwater, Nitrate Contamination

Problem and Research Objectives:

The presence of nitrate in groundwater in the Floridan Aquifer near Albany Georgia has prompted an investigation using nitrogen isotopic data to identify the source contamination. It is thought that the contamination originates from a farm and that nitrates were transported by groundwater flow to an adjacent residential community. This community’s water supply comes from homeowner wells, some of which exceed the MCL for nitrate in drinking water. A variety of materials capable of producing this contamination, such as cattle manure, biosolids (sewage sludge), and synthetic inorganic fertilizers are present or have been used on this farm. Biosolids were utilized as fertilizers over a twelve year period from 1984 to 1996 and a cattle feed lot was in operation from 1980-1984. Synthetic inorganic fertilizers were used prior to 1984. A hydrogeologic study conducted by the Georgia Geological Survey indicated that the most probable source of groundwater contamination is a disused cattle feed lot on the suspect property. To further assist in identifying the source of contamination, d15N values were measured for dissolved nitrate from nine wells both on the farm and within the residential community. The data from the contamination plume ranged from +5.5‰ to +2.3‰. This range is consistent with the idea that the major source of contamination stems from synthetic inorganic fertilizers. This conclusion is predicated on numerous studies indicating that different nitrate sources produce different ranges of d 15N values for dissolved nitrates. Typically, nitrates derived from inorganic fertilizers range from -5‰ to + 3.5‰, soil organic material from + 3.5‰ to +7.5‰, and manure and septic system effluent from +10‰ to +20‰. There are no known study of the d15N values of nitrates derived from biosolids. To reinforce this conclusion, d15N values were measured for grasses at sites where only cattle manure and biosolids were present. Analysis of plants serve as proxies for dissolved nitrate in soils because there is little or no isotope fractionation between plants and the dissolved nitrate that they uptake. The aim of this investigation was to directly assess the d15N values of dissolved nitrates in soils derived from decomposition of cattle manure and sewage sludge. A second investigation was initiated in order to constrain the age of nitrate contamination by measuring the tritium concentration of groundwaters within the area.

Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)      About…

Sponsor: GWRI
Start Date: 1998-07-01; Completion Date: 1999-12-31;
Keywords: Climate and Hydrologic Processes, Hydrology, Management and Planning
Problem and Research Objectives:

Climate variability and change pose both challenges and opportunities for the US. To be better prepared, the United States has developed a national assessment process to identify and analyze the potential consequences of climate variability and change.

Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI
Start Date: 1998-12-01; Completion Date: 1999-07-31;
Keywords: Hydrology, Management and Planning, Drought

Problem and Research Objectives:

This project intends at developing a state-of-the-art river basin planning and management system that can (a) assess the potential of the ACF basin to meet various water uses, and (b) quantify the trade-offs associated with various water allocation scenarios and policies. The purpose of this system is to assist the ongoing tri-state (Alabama, Florida, and Georgia) water allocation negotiation. The project is co-sponsored by citizen groups in Georgia.

Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI
Start Date: 1997-08-01; Completion Date: 1999-06-30;
Keywords: Climate and Hydrologic processes, Hydrology, Management and Planning
Problem and Research Objectives:

This project aims at demonstrating the value of climate and hydrologic forecasts on the operation of multi-purpose reservoirs in the US.

Short Course

Instructor: Huaming Yao (GWRI/Georgia Tech)
Instructor: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI