Category: Research

Principal Investigator: Terry W. Sturm (Georgia Tech)

Sponsor: GWRI
Start Date: 1991-04-01; Completion Date: 1992-03-31;
Keywords: Erosion, Sediment transport, Urban runoff, Settling basins, Design criteria, Urbanization

Description:
This research has focused on an evaluation of current design criteria for meeting an effluent turbidity limit in runoff from construction sites and landfills in Georgia. The research has been completed in two-phases. In Phase I, field data collected by Georgia EPD were analyzed, and the effectiveness of sediment basins in reducing turbidity was studied using numerical data generated by a computer simulation model. In Phase II, the numerical model was used to investigate the effect of changing various sediment basin design criteria, and a new sediment basin design procedure was developed. Both the field data and the numerical simulation results from Phase I showed that sediment basins can be very effective in reducing suspended sediment in runoff, but they cannot meet the turbidity standard in all cases without additional erosion control measures. In Phase II of the research, it was found that the major factor affecting sediment basin performance is soil type followed by basin surface area. The value of erosion control measures used in combination with sediment basins was demonstrated. The proposed design criteria include a detention storage based on the runoff volume from frequent storms; a minimum sediment basin surface area which is a function of soil grain size; a minimum level of erosion control; and a comparison of peak outflow sediment and water discharges with those from the undisturbed watershed. This approach provides a uniform and rational design basis for optimizing sediment basin design to meet the turbidity standard.

Principal Investigator: George Vellidis (University of Georgia)
Principal Investigator: Matt C. Smith (University of Georgia)
Principal Investigator: Richard Lowrance (University of Georgia)
Principal Investigator: Robert K. Hubbard (Southeast Watershed Research Laboratory)
Principal Investigator: Joseph C. Johnson, Jr. (University of Georgia)
Principal Investigator: Larry Newton (University of Georgia)

Sponsor: GWRI
Start Date: 1991-04-01; Completion Date: 1992-03-31;
Keywords: wetlands, restoration, bioremediation, nutrients, ground water, surface runoff, nitrogen, phosphorus

Description:
The feasibility and effectiveness of restoring a riparian wetland and using it as a bioremediation site for nutrients moving downslope from an animal waste application site is being evaluated. In question is the short-term effectiveness of the restored wetland in enhancing the quality of the water leaving the site. Details on wetland restoration and instrumentation used for measurement of nutrient movement through the wetland in surface runoff and shallow groundwater are presented. The data from the first year of restoration are inconclusive and indicate that the vegetation which was used to restore the wetland is too recently established to significantly affect nutrient assimilation and retention in the wetland. The study is being continued for an additional 2-year period at the end of which the effectiveness of the restored wetland will be reevaluated. The instrumentation, the sampling schedule, and the techniques that are described are well suited to evaluate the bioremediation potential of a restored wetland.

Principal Investigator: Lynn J. Torak (Hydrologist -U.S. Geological Survey)
Principal Investigator: Shahrokh Rouhani Ph.D (Newfields Inc)

Sponsor: GWRI
Start Date: 1991-06-01; Completion Date: 1991-06-01;
Keywords: Ground-water, Hydrogeology, Statistical Methods, Regional Analysis

Description:

The parameter estimation is a crucial phase of any ground water flow investigation, which determines the success or failure of the prediction process. The commonly used parameter-estimation approaches are based on various inverse procedures that in many instances prove to be inadequate. This report presents an advanced alternative approach which is based on the geostatistical co-estimation technique, known as co-kriging. The investigated parameters are: aqulfer transmissivity, piezometric head, and residual, which is defined as the computed minus the measured water level at a specified location. Values of computed head were obtained by using the MODular linite ~lement model (MODFE) of two-dimensional ground water flow. The data set was derived from a regional study of the Upper Floridan aquifer in southern Georgia. The initial results indicate that the log-transformed transmissivity and the uncalibrated residual are suitable for co-estimation. Direct kriging provides estimated maps for these variables, which are unbiased linear estimates with minimum variance of estimation. The co-kriging goes one step further by permitting the incorporation of measured values of both parameters in the estimation processes of each one. The results indicate that the co-kriged maps represent more spatial details with higher accuracy than their ordinary kriged counterparts. Considering the high cost of field tests in ground water investigations, the above more efficient co-estimation process offers an attractive alternative for parameter evaluation than previously used inverse procedures.

Principal Investigator: James Hook (University of Georgia)

Sponsor: GWRI
Start Date: 1990-04-01; Completion Date: 1991-03-31;
Keywords: None

Description:
Knowledge of water demands during periods of severe drought is needed to develop strategies for water management. Determination of amount and timing of water withdrawals is necessary for water managers to predict the impact of irrigation on groundwater reserves. As information becomes available on location of wells, aquifers tapped, acres irrigated, and crops managed, we will be able to anticipate water needs for irrigation. This will help in licensing new wells,anticipating seasonal drawdown, and recommending water use optimization. A first step in this examination is water use during drought years. The specific objectives of this proposal were 1) to determine the amount and schedule of agricultural demands for groundwater in years of severe droughts, and, 2) to estimate the impact of water restrictions on irrigation water use and water use efficiency.
The potential (no-water stress) and the lowest (no irrigation) yields for corn, soybean and peanut were calculated using three publicly available crop growth and water use models – CERES-Maize, SOYGRO, and PNUTGRO models, respectively. Rainfall, temperature, and solar radiation records were used with these models to identify the 15 most severe drought years in the 53 year record in the central Coastal Plain region of Georgia. Irrigation needed to bring yields into the range 80 to 90% of potential yields was determined for these drought years. Water use efficiency with and without irrigation was estimated. The amount and time of water withdrawals which could be expected for those severe drought years was calculated using the current cropping patterns and irrigated acreage in two multi-county regions in the Georgia Coastal Plain – the Dougherty Plain Region and the Georgia Cooperative Extension Southwest District.
Corn and soybean were more severely affected by drought than peanut. In the 15 driest years, yield losses for corn averaged 75% and, for soybean, 73%. For peanut, an average of 64% of the yield was lost due to drought. Of particular interest, almost half of the 15 worst drought years since 1938 occurred after 1979. The average irrigation needed to meet crop water needs was computed for 10-day periods. Most of the irrigation needs of corn in these drought years occur before irrigation is needed for peanut or soybean. Peanut and soybean needs coincide during late summer. The 36-county Southwest Georgia Extension District, contains almost 75% of Georgia’s irrigated land. In 1989 the reported irrigated land area for corn, peanut, and soybean in that region was 70,300,133,300 and 29,300 ha. The combined effect of irrigation timing and land area on water withdrawals was calculated. For most of the 130 days between late May and late September, withdrawals could exceed 3 million m3 per day, on the average, for these severe drought years. Peak water use occurred in late-July, when peanut irrigation was underway. Similar estimates were made for the Dougherty Plain area in Southwest Georgia. Further application of the techniques used here could lead to county or watershed specific estimates of maximum water needs.

Principal Investigator: Terry W. Sturm (Georgia Tech)
Principal Investigator: Ronald E. Kirby, Jr. (Georgia Institute of Technology)

Sponsor: GWRI
Start Date: 1990-04-01; Completion Date: 1991-03-31;
Keywords: Erosion, Sediment transport, Urban runoff, Settling basins, Design criteria, Urbanization

Description:
This research has focused on an evaluation of current design criteria and best-management practices for controlling sediment in runoff from construction sites in response to recent Georgia legislation which established an effluent limit on turbidity. The research approach has been two-pronged with an analysis of field data collected by Georgia EPD and of numerical data generated by a computer simulation model. The field data were collected at landfill sites which had a sediment basin. Regression relations between suspended solids in mg/l and turbidity in NTU were developed for each landfill site and were found to be dependent on the soil types at each site, which included clay loam, loam, and sandy loam. The field data indicated that the sediment basins at two of the landfill sites met the turbidity discharge standard for all storm events sampled while the sediment basin at a third site did not. It is apparent from the field data that the probability of meeting the turbidity discharge standard is dependent on rainfall characteristics, the hydrologic condition and size of the watershed contributing to the receiving stream, soil properties and soil conservation measures on the disturbed watershed, and the sediment basin design.

Computer simulation results were obtained from the model SEDCAD+ for disturbed watersheds with sediment basins designed according to the Georgia Erosion and Sediment Control Manual. The results showed that sediment basins can be very effective in reducing suspended sediment in construction-site runoff. However, for a disturbed area with significant soil-conservation treatment, the peak sediment concentration in the sediment-basin outflow exceeded the undisturbed peak concentration for a meadowland use. This was the case for storm recurrence intervals from 2 to 25 years and for all three soils tested. For an undisturbed land use of 1/3 agriculture, 1/3 woods, and 1/3 pasture, disturbed sediment concentrations in the sediment-basin outflow were less than the undisturbed values. Sediment-basin trap efficiencies obtained from the numerical model varied from approximately 45 percent for the clay loam soil to 80 percent for the sandy loam soil. The trap efficiencies decreased with increases in surface loading rate. The numerical results suggest that an improvement in the design criteria for sediment basins would be to re-define the surface loading rate and to specify lower allowable values for soils with high percentages of clay. The numerical results also quantitatively demonstrate the importance of applying soil conservation measures so as to prevent as much sediment as possible from ever reaching the sediment basin.

Principal Investigator: Ronald M. North (University of Georgia)
Principal Investigator: Jackie Sellers (University of Georgia)

Sponsor: GWRI
Start Date: 1989-04-01; Completion Date: 1990-04-01;
Keywords: water demand, forecasting, water use, demand models, water pricing, conservation.

Description:
Direct water demand estimates are useful for resolving capacity needs, system expansion, financing of systems, acquiring and issuing water use permits from water authorities and for efficient management purposes. Hickman and Associates, Inc. developed a water use forecasting system called MAIN (Municipal and Industrial Needs system). This was later adopted by the Institute for Water Resources, Corps of Engineers, our source for the program to calibrate for Georgia conditions.

Our experiences with calibrating the IWR-MAIN model were not as accurate as some of the reported calibration tests in western states. Our best reconciliation of IWR-MAIN estimate for 1990 (23.6 mgd) with data supplied by the Macon/Bibb County Water Authority (21. 8 mgd) was 7.5% higher than the water authority records, excluding public and unaccounted uses. The USGS estimated uses for publicly supplied water at 28.3 mgd was 7.6% higher than the IWR-MAIN estimate of 26.3 mgd and 15% higher than the estimate from the Macon/Bibb County Water Authority. Implementation of two conservation programs in Macon indicate water savings for out years (1990-2010) could be reduced by four to seven percent. We conclude that the IWR-MAIN water demand forecasting system would provide reasonably consistent results because of the standard methodology used if it were applied throughout the state of Georgia.

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

Description:
The objective of this research is to evaluate field methods for estimating streamflow reductions due to pumping from nearby wells. This project is a supplement to previous work which provided a microcomputer model for estimating streamflow depletion due to pumping from nearby wells. Four direct measurement techniques and one indirect estimation technique are described and evaluated for estimating induced recharge through stream bottoms for phreatic and confined aquifers. Direct techniques are seepometers, minipieozmeters, temperature probes, and tracers. The indirect estimate is derived from streamflow correlations. Streamflow correlation estimates and tracers are not generally useful. Seepometers, minipiezometers, and temperature probes are useful for both phreatic and confined aquifers subject to certain bottom sediment and flow volume constraints.

Seepometers, minipiezometers, and temperature probes can be used to measure groundwater discharge from phreatic aquifers through fine-grained and relatively porous bottom sediments such as silts and sands. All three methods require clusters of at least five identical instruments to be installed at each of several measurement points in the stream bottom to properly assess micro- and meso-scale variability in sediment composition and groundwater flux patterns. Seepometers are the easiest to use and directly measure vertical flux through the stream bottom. Minipiezometers require accurate measurements of sediment saturated vertical hydraulic conductivity over the depth sampled, and temperature probes require the measurement of sediment specific heat and specific density and the thermal conductivity of the sediment-fluid complex. None of these three methods can be used in dense clay bottom sediments.

Seepometers and minipiezometers are inappropriate for estimating impacted discharge from confined aquifers. Springs are useful in assessing changes in discharge from confined aquifers. If local conditions do not allow installation of a V -notch wier or other precise instrumentation to directly measure spring discharge, then temperature probes can be used if the discharge volume and temperature gradient are sufficient to change the ambient stream temperature passing the spring during lowflow conditions. Temperature probes are easy to fabricate, install, and automatically monitor

Principal Investigator: Gian S. Ghuman (Savannah State College)
Principal Investigator: Kamalakar B. Raut (Savannah State College)

Sponsor: GWRI
Start Date: 1988-06-01; Completion Date: 1989-07-01;
Keywords: ion exchange, soil erosion, solute transport, toxic substances.

Description:

During 1988-89, release of major and toxic (trace) metals from two soil types in coastal Georgia was studied regarding the impact of rainfall. Results were compared in the runoff water from plots under grass and forest vegetation. Leaching experiments were conducted to evaluate the effect of two leaching solutions on the downward transport of metals. Runoff water samples were collected from four field plots (4m x 4m) into plastic buckets via a spillway laid-out in the corner of each plot. Four periodic collections of samples of runoff water were made after significant rainfall events from August to September, 1988. Water samples were filtered through 0.45 mMillipore filters and their pH was adjusted to 2.0 for the estimation of metals by atomic absorption spectroscopy. Six sequential leachings were conducted in 40 cm long (6 cm I.D.) PVC columns packed with reconstructed field soil profiles to a depth of 36 cm. Two leaching solutions were, (i) deionized water adjusted to pH 6.5 with nitric acid, and (ii) deionized water adjusted to pH 5.0 with carbon dioxide. Exchangeable metals of the surface soil were determined in IN ammonium acetate extract. In both the runoff water and the leachates, there was greater removal of metals from forested soil than the grass-covered soil. Losses of K and Na far exceeded the losses of Ca and Mg. Release of K was consistent in both sandy and loamy soil plots probably due to K-rich minerals in coastal soils. Slightly high concentrations of Mn, Ni, Zn and Cu and low concentrations of Cd were released by both mechanisms (runoff and leaching), but all were below toxic limits. Removal of trace metals was greater by acidified water than by carbonated water. Ammonium acetate-extractable metals were diminished in the forested soil due to its lower pH than the grass-covered soil. Resutls are important for the maintenance of soil fertility and observing the quality of effluent water to prevent any toxicity.

Principal Investigator: James L. Cooley (University of Georgia)
Principal Investigator: Gail M. Cowie (University of Georgia)

Sponsor: GWRI
Start Date: 1989-04-01; Completion Date: 1989-04-01;
Keywords: watershed protection, watershed management, land use, planning, municipal water, water supply, water quality, water quality management

Description:

In Georgia, recent years have seen an increasing emphasis on watershed protection as a critical component of water supply planning. Effective watershed management requires significant action at the local level. However, many local officials have limited understanding of water quality protection techniques and methods for planning watershed management programs. The objective of this research was development of guidelines, clearly useful to local officials, for watershed protection planning at the local level. Development of guidelines began with a survey of existing watershed protection programs in the Southeast. Preliminary elaboration of a planning process was based on evaluation of thirteen proposed water supply watersheds in Northeast Georgia. The planning process was further refined through detailed analysis of three of these watersheds. Results for the study watersheds are presented with specific discussion of considerations in watershed protection planning.

As defined through this research, the planning process has seven distinct portions: 1) preliminary statement of objectives; 2) watershed assessment; 3) highlighting of areas that require particul~ attention in the management program; 4) refining objectives with public input; 5) definition of alternative watershed protection packages; 6) screening to select the preferred alternative; and 7) planning for implementation and evaluation of program effectiveness. Several components are fundamental to this planning process and make it adaptable to water supply watersheds across north Georgia. First, the process needs to be individually applied to specific watersheds. Second, a variety of technical solutions to watershed protection problems exist. For a watershed protection program to be effective, specific solutions for particular watersheds must be defined by citizens and officials from the locality. Finally, public education and participation is integral to successful application of the watershed protection planning process.

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.