Category: Research Sponsored by GWRI

Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI
Start Date: 1988-03-01; Completion Date: 1988-03-01;
Keywords: Streamflow Forecasting, Reservoir Operation, Hydropower, Flood

Description:
The value of streamflow forecasts in reservoir operation depends on a number of factors and may vary considerably. Assessment of forecast benefits is presented here for three specific systems. Statistical streamflow models of increasing forecasting ability are coupled with a recently developed stochastic control method in extensive simulation experiments. The systems’ performance is statistically evaluated with regard to energy generation and flood and drought prevention. The results indicate that forecast benefits are system specific and may range from quite substantial to fairly minimal.

Principal Investigator: John F. Dowd (University of Georgia)
Principal Investigator: Kathryn J. Hatcher (University of Georgia)
Principal Investigator: Phillip J. Smith (University of Georgia)
Principal Investigator: John F. Dowd (University of Georgia)

Sponsor: GWRI
Start Date: 1987-07-01; Completion Date: 1987-07-01;
Keywords: surface-groundwater relationships, groundwater, water management, conjunctive use, wells, regulation, streamflow, groundwater models

Description:
A groundwater model for estimating streamflow reductions due to pumping from nearby wells was developed. The model can be used to evaluate well permit applications for groundwater withdrawals. The computer program is based upon an analytical solution of a two-dimensional planimetric representation of a stream/aquifer system in a semi-infinite domain. The variables required are transmissivity, pumping rate, well location, and aquifer storativity. The program calculates drawdown in the aquifer, drawdown adjacent to the stream, amount of flow induced from the stream into the aquifer, and total contribution from the stream into the well for four time steps per simulation. The program runs interactively on IBM-PC-compatible microcomputers. Results are presented through a summary table and high-resolution graphics when hardware graphics support is available. Output options include line graphs of drawdown along the stream, flow from the stream into the aquifer, and a contour plot of water table drawdown.
The completion report also includes a sensitivity analysis of the computer program for ranges of data likely to be encountered in the southeastern coastal plain is presented. The results illustrate the relative influence of each input parameter and highlight critical data needs for permit evaluation. The results indicate that for many combinations of field conditions and sustained pumping, 90% or more of the total well withdrawal is derived from nearby streams.

Principal Investigator: Shih-Chao Chiang (Georgia Institute of Technology)
Principal Investigator: David E. Radcliffe (University of Georgia)
Principal Investigator: Shih-Chao Chiang (Georgia Institute of Technology)
Principal Investigator: William P. Miller (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1987-03-01; Completion Date: 1987-03-01;
Keywords: flocculation, soil erosion, infiltration, permeability

Description:
Lateral movement of infiltrating water frequently occurs at the surface of Southern Piedmont soils and may occur below the surface when dense layers are present at a shallow depth. Our objective was to determine to what extent lateral movement occurred and what mechanisms might be responsible for the low permeability. Because of equipment problems with a field rainfall simulator we were unable to address subsurface lateral flow, but a greenhouse and laboratory experiment provided information on surface lateral flow. In Experiment I., infiltration rates declined steadily in three soils, two of which had final infiltration rates so low that run-off would occur under all but very low intensity rainfalls. The decline in infiltration was attributed to dispersion of soil particles upon impact by raindrops and the formation of a low permeability washed-in layer of dispersed clay particles just below the surface. In Experiment II, it was shown that soil dispersion varied among soils and could be severe when infiltrating water was low in mineral content (eg. rainfall) and soil pH had been raised through liming.

Principal Investigator: Shahrokh Rouhani Ph.D (Newfields Inc)
Principal Investigator: Timothy J. Hall (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1987-03-01; Completion Date: 1987-03-01;
Keywords: Network Design, Statistical Methods, Regional Analysis, Water Quality, Water Management (Applied), Georgia.

Description:

Geostatistical schemes for ground water quality monitoring in the shallow aquifer of Dougherty Plain, Georgia are presented. This aquifer is not generally used for water supply purposes. However, it is the main recharge route to the principal artesian aquifer which is the primary source of water supply in this rapidly growing agricultural region. The desired monitoring network acts as an early warning system for ground water pollution in deeper layers. We have utilized the available data on hydraulic properties of the shallow aquifer to identify the zones which should be the primary locations for our sampling activities. The one variable which appears to be most suitable for our study is leakance. Statistical analyses indicate that leakance has a log-normal distribution with a constant trend and a linear covariance function. Ranking criteria for the selection of the best sampling points are: the variance reductions, the medians, and the risk values. Due to the nature of our monitoring network we suggest to use mainly risk ranking as the basis of our sampling activities. The results of our risk rankings demonstrate that the southern tip of the Dougherty Plain’ and its upper central zone should be the prime targets of our monitoring activities.

Principal Investigator: M. M. Aral (Georgia Institute of Technology)
Principal Investigator: E. H. Haddad (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1986-04-01; Completion Date: 1987-03-01;
Keywords: Ground water seepage, Finite element method, Multilayer aquifers, Aquifer management.

Description:

The study summarized in this report is directed toward gaining additional knowledge on the unsteady performance of multilayer aquifers in response to heavy withdrawal of water from several wells distributed in the system. A recent status report on ground water problems in South Eastern United States clearly indicates that more detailed information is needed on this problem in order to describe appropriate management options for such multilayer aquifer regions. In the first phase of this modeling effort which was published in 1985, steady state ground water flow equations were studied and a steady ground water flow model was developed for multilayer aquifers. The second phase of the study, reported here, extends the steady state model to an unsteady multilayer ground water flow model which prepares the stage for contaminant transport model in multilayer aquifers which is the last phase of these model development efforts.

In the present study a regional two-dimensional flow analysis is formulated using finite element techniques for multilayer aquifers. Numerical solutions are presented to test the accuracy and efficiency of the proposed technique.

Principal Investigator: Peter E. Sturrock (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1986-04-01; Completion Date: 1987-02-01;
Keywords: Electrochemical Detection, HPLC, Azo Dyes.

Description:

The research summarized in this report investigated the application of a new electrochemical detector to the high-performance liquid chromatographic analysis of water for azo dyes. The detector is a computer-controlled device capable of being programmed to operate in many modes. Rapid-sweep square-wave voltammetry, the preferred mode of operation where applicable, was applied successfully to the azo dyes. For these compounds, the detector is more sensitive than a photometric detector, and the swept mode of operation is useful in resolving components not separated completely by the chromatographic column.

Principal Investigator: Richard Lowrance (University of Georgia)
Principal Investigator: Adel Shirmohammadi (University of Maryland)
Principal Investigator: Daniel L. Thomas (University of Georgia)

Sponsor: GWRI
Start Date: 1986-04-01; Completion Date: 1987-03-31;
Keywords: drainage, water quality, nitrates, ammonium, phosphates, pH, chlorides, electrical conductivity, drainage quality, water quality sampling, subirrigation.

Description:

Nitrate-N, Ammonium-N, Phosphate-P, pH, electrical conductivity, and chloride concentrations were measured from shallow subsurface wells and outlets of a drainage-subirrigation system in the Georgia flat woods. These data were compared to shallow subsurface water quality from adjacent forested and cleared areas using Duncan’s Multiple Range Test at the 0.05 level. A simulation of the nutrient movement from an area representative of the study site was also performed for a preliminary evaluation of the models applicability to the Georgia flat woods region.

Nitrate-N concentrations were significantly higher in the drained-subirrigated area than in the forested and cleared areas. Nitrate-N concentrations did not exceed 10 mg/l from any of the ouflow samples even though several infield samples did exceed this limit. Ammonium-N concentrations were not high and do not appear to be a problem in this drainage-subirrigation system based on the limited data available for this report. No significant differences were found between sites, but the sample size may not have been large enough to show a significant difference.

Phosphate-P concentrations were relatively low as compared to other water quality studies and only one site (cleared-unirrigated area) had significantly higher phosphate-P concentrations from all the other sites. The low phosphate-P concentrations of the outflow samples (less than 0.05 mg/l) indicates that the low clay content, sandy soils of this area have considerable ability for phosphate-P fixation and may not promote excessive leaching of phosphates.

The pH of all the shallow well sites were significantly lower then the inflow, outflow and surface water samples. However, the extremes in the pH measurements were not great enough to cause concern. The effect of the water supply on the outflow samples during the irrigation phase was evident in the pH results. The benefits of using alternative water supplies to reduce potential problems associated with the pH of outflow water needs further study.

The electrical conductivity and chloride concentrations from the drained-subirrigated areas indicates a potential problem if sufficient rainfall does not occur during the growing season to leach the salts. Significantly higher chloride concentrations were found in the drained-subirrigated field than in the cleared and forested areas. The drought period in 1986 showed a marked increase in chloride concentration under the drainage-subirrigation field, but the levels decreased after sufficient rainfall leached the salts from the soil.

Research is continuing on the evaluation of these water quality parameters to further verify the results presented in this report.

Preliminary simulations using CREAMS-WT (a derivative of the CREAMS model) on a field with similar characteristics to the drainage-subirrigation site, indicate that the potential nutrient losses in surface runoff were not severe. The model is not designed to simulate forested or cleared conditions so comparisons with existing conditions were not available

Principal Investigator: Boris M. Khudenko (Georgia Institute of Technology)
Principal Investigator: Harold F. Wiedeman (Georgia Institute of Technology)
Principal Investigator: Joseph P. Gould (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1986-07-01; Completion Date: 1986-07-01;
Keywords: Cadmium, Magnesium, Resource Recovery, Hazardous Wastes, Toxic Substances, Industrial Wastes, Waste Treatment

Description:
The kinetics of cementation of cadmium by magnesium were studied in a completely mixed batch reactor at room temperature and constant mixing rate and ionic strength. Magnesium strips provided in stoichiometric excess were used as electrodes. The effect of pH and initial cadmium concentration on the rate of cadmium removal and reaction stoichiometry, or yield of magnesium consumed per cadmium cemented, were evaluated.

The rate of cadmium removal was shown to be independent of pH between 3 and 6. However, as pH increased, the process yield became more favorable. This was attributed to the competing reaction of magnesium dissolution which decreases with increasing pH. The rate of cadmium removal was studied at initial cadmium concentrations between 1 and 100 mM. It was found that the rate and stoichiometry were highly dependent upon initial cadmium concentration.

At initial concentrations of up to approximately 25 mM, the reaction was found to follow apparent half order kinetics consistent with a migration control mechanism. As initial cadmium concentrations increased through this range, removal rates also increased. At approximately 25 mM, a transition was observed to apparent first order kinetics consistent with a diffusion control mechanism. There was a significant decrease in removal rates as the initial cadmium concentration increased to levels of greater than 25 mM.

Stoichiometry was found to become more favorable as initial cadmium concentration increased, and in some cases, less than 1 mole of magnesium was required to cement 1 mole of cadmium. This effect was attributed to electrolysis of water by the induced electrochemical system.

Principal Investigator: John C. Kabouris (Georgia Institute of Technology)
Principal Investigator: Aris Georgakakos (GWRI/Georgia Tech)

Sponsor: GWRI
Start Date: 1986-07-01; Completion Date: 1986-07-01;
Keywords: Unit Hydrographs, Markov Process, Streamflow Forecasting, Infiltration, Surface Runoff. Watershed Management.

Description:
A physically-based methodology for streamflow forecasting is researched and implemented. Watershed response is modelled as Continuous-Time Markov process whose states include both surface and subsurface runoff components. Based on probabilistic arguments, time-varying Instantaneous Unit Hydrographs are derived and convoluted with antecedent rainfall intensities to generate streamflow discharges. The method is applied to the Little River Watershed in South Georgia with encouraging results. Such models are useful in quantifying the response of ungaged watersheds and predicting streamflows in real time. In turn, such studies are instrumental in the design and operation of reservoirs.

Principal Investigator: Jack H. Reeves (The University of Georgia)
Principal Investigator: William P. McCormick (The University Of Georgia)

Sponsor: GWRI
Start Date: 1986-07-01; Completion Date: 1986-07-01;
Keywords: Low Flow Frequency, Design Flow, Time Series Analysis

Description:
In this report we analyze three problems related to a design low flow called the seven day, ten year minimum streamflow ,(7Q1O). The 7Q1O denotes the tenth percentile of the distribution of the streamflow, which gives for a one year period the lowest level of streamflow for which there was a seven consecutive day period with flows below that value on each day. The 7Q1O is commonly used as an annual design low streamflow for determining waste water discharge permit specifications.

The first problem we address is to determine monthly design low streamflow values. A method of assigning design low flow values which can vary over the year is of interest in order to allow greater use of the stream for diluting waste water discharges. We offer a simple method for calculating monthly design low flow values, which does not lead to any greater number of daily contraventions below the monthly design flows than that which already occurs for the one fixed annual 7Q1O method.

The second problem addressed concerns the estimation of 7QIO with a confidence interval. We offer a method based on a model for daily streamflows, and we compare our estimation procedure with two other often used procedures.

The third problem concerns the estimation of 7Q1O when the record of streamflow is only partial and short. We recommend a procedure which incorporates the use of rainfall data into our estimation procedure for 7Q1O.