Category: Research Sponsored by GWRI

Principal Investigator: Terry W. Sturm (Georgia Tech)

Sponsor: GWRI
Start Date: 2003-03-01; Completion Date: 2004-02-28;
Keywords: fluid flow, hydraulics, instream flow, river beds, rivers, sedimentation, sediment load, sediment TMDL, nonpoint pollution, urban hydrology

Abstract:

Sediment loads and water quality are inextricably linked in Georgia streams, particularly in urban areas in the piedmont region where fine-grained sediments contribute turbidity in the water column and deposition in downstream areas. Urbanization results in increased washload to the stream due to runoff from construction sites that are inadequately protected by erosion control measures. In addition, the runoff volume and peak discharge increase due to an increase in impervious area on the watershed. The result is a loss of equilibrium in the sediment regime of the stream. The consequences include bank erosion, degradation, loss of aquatic habitat and spawning areas, inhibition of photosynthesis due to turbidity in the water column, increased water treatment costs, loss of reservoir storage capacity, and transport of contaminants associated with fine sediments. The resulting impairment of water quality has to be addressed with respect to compliance with section 303(d) of the Clean Water Act. In particular, where excess sediment loads threaten the biological integrity of streams, TMDLs (total maximum daily loads) must be established to quantify allowable sediment loads for the purpose of controlling the sources of water quality impairment. The development of TMDLs for sediment is complex because of various in-stream processes that contribute to the problem as well as watershed sources of sediment. The objectives of the proposed research are to develop a procedure for: (1) measuring sediment loads in streams due to both watershed sediment yield and in-stream processes; and (2) evaluating the contribution of in-stream processes such as bed and bank erosion to the sediment budget of stream reaches selected for establishment of TMDLs. The objectives will be achieved through a combination of field measurements on an urban stream and numerical modeling of sediment loads and stream stability.

Principal Investigator: Paul Work (GTREP – Savannah)

Sponsor: GWRI
Start Date: 2002-03-01; Completion Date: 2003-02-28;
Keywords: Sediment, Non Point Pollution, Surface Water

Description:

This report discusses the techniques for data collection in Hartwell Lake and presents the analyzed data. Three types of data were collected in Hartwell Lake between February 10th and February 13th, 2003: bathymetry, velocity and shoreline position data. Depth data were collected using a dual frequency depth measuring system. Velocity data were measured using a 1200 kHz Acoustic Doppler Current Profiler (ADCP), and shoreline data were provided by a differential global positioning system (GPS). During the bathymetric surveys and velocity measurements a handheld GPS was also integrated with the devices for navigation.

Comparison of bathymetric surveys to previous surveys provided by USACE indicated approximately 2  0.27 meters of deposition over 40 years within the thalweg.

The hydrodynamics of the lake were modeled using a numerical model previously. In this study, surface velocities are measured in the main pool of the lake to validate results of the numerical model. Strong winds (more than 4 times the historical average) from the southwest were observed during the measurement period. Maximum measured surface velocities at several transects were ~50 cm/s and average velocities were ~25 cm/s.

Principal Investigator: Judith Meyer (University of Georgia)

Sponsor: GWRI
Start Date: 2001-03-01; Completion Date: 2002-02-28;
Keywords: Ecosystem processes, Basin-wide analysis for water management, Solute transport, Flow regime, Apalachicola-Chattahoochee-Flint River Basin

Problem and Research Objectives:

The quantity and timing of river flow is critical to the ecological integrity of river systems (Poff et al.1997). Flow is strongly correlated with physical and chemical characteristics of the river such as channel shape, water temperature and velocity,and habitat type and complexity (Jowett and Duncan 1990,Poff et al.1997). Five main components of the flow regime impact ecological processes:magnitude of discharge at critical time periods,frequency of the various discharge magnitudes,duration of time associated with a particular discharge,timing or predictability of discharge events of particular magnitudes,and the rate of change of hydrologic conditions (Richter et al. 1996,Poff et al.1997) .These five components of the flow regime influence the ecological dynamics of river systems directly and indirectly by affecting water quality, energy sources,physical habitat,and biotic interactions (Karr 1991,Poff et al.1997).

Although there are many different types of hydrologic and channel alterations that result in changes to the flow regime,dams are one of the most conspicuous and prevalent forms of flow alteration on large and some smaller rivers and streams.In the contiguous United States,there are only 42 rivers with greater than 200 river kilometers unregulated by major dams (Benke 1990).Though there have been a number of studies of the impacts of dams on channel morphology (Ligon et al.1995),fish (Moyle et al.1998), habitat availability (Bogan 1993),and riparian species survival and recruitment (Rood et al.1995),less is known about the impact of dams and flow regime on basic ecosystem processes such as nutrient uptake and metabolism,especially in larger rivers.In many cases,these ecosystem processes are directly linked to the ecosystem services (e.g.water supply,pollution control, and fisheries)expected from the river system.

We are studying the relationship between flow and nutrient uptake and metabolism on the Chattahoochee River below Atlanta.The fixation of energy through primary production and the subsequent release through respiration are primary ecosystem functions,and the addition or loss of energy to the system can influence energy flows in downstream systems.In order to determine net addition or loss of energy to the system, net daily metabolism can be calculated.Net daily metabolism is defined as the difference between gross primary productivity and total system respiration (Bott 1996). Metabolism has been shown to vary with high stream discharge as a result of shifts in primary production (Uehlinger and Naegeli 1998).However,relationships between net daily metabolism and low flow conditions are uncertain,particularly in large river systems.

The uptake and processing of nutrients by rivers is essential to maintaining downstream and instream water quality.In unregulated rivers,the downstream ecosystems that could be affected by high nutrient loadings are typically estuaries. However,in regulated rivers,there are typically a series of reservoirs that are connected by sections of flowing water.This is the situation on the Chattahoochee River.In addition,the flowing river section between Lake Lanier and West Point Lake receives approximately 220 million gallons a day of wastewater treatment plant effluent (Frick et al.1996).The retention and transformation of the nutrients associated with these inputs is essential to maintaining water quality in this section of the river and in West Point Lake.Nutrient uptake length is the length of stream traveled by the average nutrient molecule in the water column before being taken up by biota (Stream Solute Workshop 1990).Nutrient uptake lengths in small streams is related to discharge (Stream Solute Workshop 1990).Uptake lengths in streams receiving wastewater treatment plant effluent are typically much longer than uptake lengths in streams with similar discharge but no wastewater inputs (Marti et al.In press).However,it is uncertain how nutrient uptake lengths vary with low flows in large rivers.

Our objectives were to determine how net ecosystem metabolism and nutrient uptake lengths vary with discharge under baseflow conditions in the Chattahoochee River below Atlanta.In addition,we wanted to determine the importance other factors that may influence metabolism and nutrient uptake such as temperature,total suspended solids,light,dissolved organic carbon,water column chlorophyll a concentrations,and nutrient concentrations.We hope that these analyses will help to give a better understanding of how flow regime influences ecosystem processes in a regulated river.

Principal Investigator: Elizabeth Blood (Albany State University)

Sponsor: GWRI
Start Date: 2002-03-01; Completion Date: 2003-02-28;
Keywords: Management and Planning

Problem Statement:

The Flint River Basin is in the cross-hairs of public policy debate on water. Atlanta resides in the headwaters, irrigated agriculture in the lower basin, and the entire basin is a critical component of the Alabama, Georgia, and Florida interstate water compact negotiations. Concerns over unsustainable consumption of water resulting from uncontrolled growth of metro-Atlanta; water quality issues associated with this urbanization; and agricultural withdrawals of groundwater in southwest Georgia have made water the focus of public policy debate. Conflicts are arising over these water withdrawals to fuel growth, the economy, and sustain the natural resources. During the past four years, these concerns have been heightened by the most severe and prolonged drought of record. This drought has resulted in record low flows and water levels in reservoirs and aquifers; water restrictions and bans; domestic and municipal well failures; communities with fewer than two weeks municipal reserves, and negative impacts on natural resources have raised concerns over long-term water security.

An effective water management strategy is clearly needed to address these challenges and provide a fair and equitable process to allocate and sustain the water resources. The North Georgia Metropolitan Planning District was the first regional strategy created to address the water resource issues. The plan encompasses sixteen counties forming the Greater Atlanta metropolitan area including the upper basin of the Flint River. The Flint River Basin has distinct regional differences in water issues, concerns, and values; sociology; economy; natural resources; governance; and management infrastructure. The formal structure and organization of the metro plan will not work for rural Georgia or the lower Flint River basin. Water decisions, management, regulation and infrastructure are controlled by county, municipal, or organizational entities in the upper basin. In the lower basin, water decisions, management, and infrastructure are primarily controlled by individuals. County and municipal oversight is restricted to a few larger cities. The water management plan; the planning process and organizational structure; and the implementation options, infrastructure, and policy must be developed to incorporate regional perspectives, values, opportunities, and resources.

Principal Investigator: Ching-Hua Huang (Georgia Tech)

Sponsor: GWRI
Start Date: 2002-03-01; Completion Date: 2003-02-28;
Keywords: Water Quality, Water Treatment, Wastewater

Description:

Results of this study indicate that representative members of three environmentally relevant antibiotic classes – fluoroquinolones, sulfonamides, and dihydrofolate reductase (DHFR) inhibitors – are substantially degraded under conditions simulating chlorination of water supplies during disinfection processes, yielding a wide variety of lower and higher mass degradates. The mechanistic understanding of the reactions between chlorine and these three antibiotics classes provides a critical basis for predicting the fate of related antibiotics and pollutants in the chlorination disinfection processes.

Principal Investigator: Bruce Beck (University of Georgia)

Sponsor: GWRI
Start Date: 2001-03-01; Completion Date: 2002-02-28;
Keywords: Surface Water, Iron, Nutrient Dynamics, Phosphorus

Introduction:

The complex interactions iron and phosphorus play a primary role in the availability of phosphorus in surface waters of the Georgia Piedmont. Exploration of these dynamics can provide information for nutrient management in surface water systems of this region. The soils of the Georgia Piedmont are rich in iron primarily as iron hydroxides (oxidized iron). Iron hydroxides form a ligand exchange with phosphate ions, making the phosphate biologically unavailable. Phosphorus, particularly inorganic phosphate, delivered through non-point source runoff to receiving waterbodies may be sorbed to iron hydroxides and not biologically available, while phosphorus, as organic phosphorus, delivered from a point source (such as an effluent pipe) may be immediately biologically available. Illuminating the biogeochemistry of phosphorus in surface waters rich in iron hydroxides will provide information useful in setting local water quality criteria and standards, and will help define the relationship between point and non-point pollution in surface waters receiving runoff from iron-rich soils.

The paradigm for phosphorus cycling was developed based on data from lakes in northern temperate regions. Lakes in north temperate regions tend to be glacial in origin. The phosphorus cycling paradigm in north temperate systems involves the sinking of inorganic particulates and organic material which result in a steady increase in dissolved phosphorus in the hypolimnetic waters of strongly stratified lakes. The dissolved phosphorus is then recirculated to the lake at fall mixis (Hutchinson 1957; Wetzel 1983; Goldman and Horne 1994). In contrast, Southeastern Piedmont lakes are primarily man-made impoundments. The climate in the southeastern US provides for a longer growing season and warmer annual average temperatures than those found in north temperate regions. This difference in climate affects the strength and length of summer stratification, and creates the conditions for monomictic rather than dimictic lakes in the southeastern Piedmont. The parent geology of the southeastern Piedmont is responsible for the differences in the cycling of phosphorus in southeastern Piedmont systems. The high iron content of the soils in the southeastern Piedmont provides transport of iron via runoff to aquatic systems in this region. The steady increase in hypolimnetic P during stratification, and the pulse of soluble P at fall turnover, is not found in southeastern Piedmont lakes. Oxidized iron in the water column binds phosphate via surface sorption and ligand exchange. We hypothesize that this sorption removes inorganic phosphorus from the biologically available fraction, thus creating a different lake phosphorus cycling regime for systems in the southeastern Piedmont.

We investigated the biogeochemical processes involved in the cycling of phosphorus as phosphate in the iron-rich waterbodies of the Georgia Piedmont. We explored the sorption chemistry of iron and phosphorus using the chemical equilibrium model MINTEQ. We conducted laboratory studies of the geochemical processes involved in phosphorus and iron interactions in surface water. We also conducted corresponding fieldwork on Lake Lanier sampling metals and phosphorus at depth four times in the annual cycle, to investigate the current roles of iron and phosphorus in the surface waters of Lake Lanier. The work conducted in this study will allow us to help identify appropriate in waterbody concentrations of phosphorus, given the local geochemistry, for local waterbody specific water quality criteria and standards, and may help evaluate appropriate parameters for monitoring significant changes in water quality of Lake Lanier.

The MINTEQ model program was released initially by USEPA in 1991 as a chemical equilibrium model for the calculation of dilute aqueous solutions in the laboratory or in natural aqueous systems. The model can calculate the equilibrium mass distribution among dissolved species, adsorbed species, and multiple solid phases under a variety of conditions and gas phase partial pressures. MINTEQ comes complete with a comprehensive database, and also allows for user defined parameter input [http://www.epa.gov/ceampubl/minteq.htm]. We used the VMINTEQ model program, which is a modified form of the MINTEQ model to explore the iron-phosphorus chemistry of Georgia Piedmont lake systems. VMINTEQ has been modified by the addition of a Visual Basic interface and the Stockholm Humic Model sub-model to include dissolved organic matter interactions using the diffuse layer model rather than the Gaussian distribution for organic matter physical chemistry (Gustaffson 2001). The laboratory experiments we conducted utilized the results of the model runs to determine initial conditions for the sorption capacity experiments.

The laboratory experiments were conducted in multiple phases. The first phase involved 24 and 48 hour sorption capacity experiments. The second phase involved measuring changes in sorption of phosphorus to iron in the presence of elevated organic matter introduced as concentrated humate in the form of Agrolig powder. The final phase of the planned laboratory work involving algal response to additions of iron complexed phosphorus was not completed due to time and funding constraints.

The third component of our work included depth measurements of metals, nutrients, and basic water chemistry parameters taken four times in the annual cycle on Lake Lanier. We analyzed these data to evaluate the hypothesis that phosphorus cycling in Georgia Piedmont lakes differs significantly from the northeast temperate lake paradigm. Measurements at depth of iron, manganese, and phosphorus show the lack of phosphate in the anoxic bottom waters, and the lack of soluble iron at the sediment-water interface. These measurements help define the role of iron in the phosphorus cycle in Georgia Piedmont lakes.

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.