Category: Research

Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI
Start Date: 2000-04-15; Completion Date: 2002-02-14;
Keywords: Flow requirements, In-stream Biological Integrity, Trade-off Analysis, Interbasin Transfer

Scope of Study:

The purpose of this study is to assess the response of the ACF river basin to biological integrity requirements. These requirements are quantified in a preliminary guidance document drafted by US EPA and the Fish and Wildlife Service (1999).

Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI
Start Date: 2001-03-01; Completion Date: 2002-02-28;
Keywords: Basinwide planning, Decision support systems, Irrigation assessment, Technical

Abstract:

The water resources systems of the Southeastern U.S. are increasingly stressed by various demands. This stress is magnified during the periodic periods of drought that occur in the region, and agriculture is particularly affected by these droughts. Recent public policy has attempted to mitigate the impacts on farmers, but reliable methods of drought assessment and forecasting are needed to allow efficient policy implementation. A methodology is presented to assess the effects of droughts on crop yields, irrigation demands, and the full yield- irrigation relationship. The technique utilizes irrigation optimization algorithms coupled with physiologically based crop models. Ensembles of climatic forcing allow for quantification of the stochastic crop-water production function at specific sites and quantification of the changes in this function in drought periods. Data needs for assessment are discussed as well as sensitivity of the methodology to some input parameters. The technique is applied to four case study sites in southwestern Georgia, and potentially useful information is derived. Options for drought forecasting are briefly discussed.

Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI
Start Date: 1999-07-01; Completion Date: 2001-06-30;
Keywords: Surface aquifer linkages, Irrigation supply, Hydrologic budget

Project Description:

In the coastal area of Georgia, ponds are sometimes excavated at golf courses, farms, or communities by digging through sandy surface soils until the water table is reached. These man-made seepage ponds are often used to supply water for irrigation, and are thus a potential supplemental source of water to the Upper Floridan aquifer. Because the potential availability of water from seepage ponds is poorly understood in coastal regions, a test site will be selected for detailed evaluation.

This course will review the fundamentals of turbulence modeling for flows of engineering interest, discuss the latest advancements in model development and applications, and address a number of issues that are critical for successful numerical simulations of turbulent flows. The main emphasis will be on closure models for the Reynolds-averaged Navier-Stokes equations, as they provide the only practical framework for modeling complex flows. Isotropic eddy-viscosity models, non-linear eddy-viscosity models and algebraic and transport Reynolds-stress models will be presented and their relative performance in a number of complex benchmark flows will be discussed. Special emphasis will be placed on approaches for modeling the structure of turbulence near smooth and rough walls and free-surfaces as well as on turbulence models for sediment-laden and stratified flows. Numerical issues regarding the robust and efficient implementation of turbulence models in CFD flow solvers will also be emphasized.

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.