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R.B. Randolph

Publications and source records attributed to R.B. Randolph.

6 recordsLinked to original sources
USGS1986

Methods and computer program documentation for determining anisotropic transmissivity tensor components of two-dimensional ground-water flow

The theory of anisotropic aquifer hydraulic properties and a computer program, written in Fortran 77, developed to compute the components of the anisotropic transmissivity tensor of two-dimensional groundwater flow are described. To determine the tensor components using one pumping well and three observation wells, the type-curve and straight-line approximation methods are developed. These methods are based on the equation of drawdown developed for two-dimensional nonsteady flow in an infinite anisotropic aquifer. To determine tensor components using more than three observation wells, a weighted least squares optimization procedure is described for use with the type-curve and straight-line approximation methods. The computer program described in this report allows the type-curve, straight-line approximation, and weighted least squares optimization methods to be used in conjunction with data from observation and pumping wells. Three example applications using the computer program and field data gathered during geohydrologic investigations at a site near Dawsonville, Georgia , are provided to illustrate the use of the computer program. The example applications demonstrate the use of the type-curve method using three observation wells, the weighted least squares optimization method using eight observation wells and equal weighting, and the weighted least squares optimization method using eight observation wells and unequal weighting. Results obtained using the computer program indicate major transmissivity in the range of 347-296 sq ft/day, minor transmissivity in the range of 139-99 sq ft/day, aquifer anisotropy in the range of 3.54 to 2.14, principal direction of flow in the range of N. 45.9 degrees E. to N. 58.7 degrees E., and storage coefficient in the range of 0.0063 to 0.0037. The numerical results are in good agreement with field data gathered on the weathered crystalline rocks underlying the investigation site. Supplemental material provides definitions of variables, data requirements and corresponding formats, input data and output results for the example applications, and a listing of the Fortran 77 computer code. (Author's abstract)

Open-File Report↗
USGS1985

Comparison of aquifer characteristics derived from local and regional aquifer tests

A comparison of the aquifer parameter values obtained through the analysis of a local and a regional aquifer test involving the same area in southeast Georgia is made in order to evaluate the validity of extrapolating local aquifer-test results for use in large-scale flow simulations. Time-drawdown and time-recovery data were analyzed by using both graphical and least-squares fitting of the data to the Theis curve. Additionally, directional transmissivity, transmissivity tensor, and angle of anisotropy were computed for both tests.

Groundwater↗
USGS1984

Analysis of the effects of proposed pumping from the principal artesian aquifer, Savannah, Georgia area

A two-dimensional finite-difference model of the principal artesian aquifer in the Savannah, Georgia, area, originally developed by Counts and Krause (1976), has been expanded and refined. The model was updated and the grid redesigned to provide more current and accurate detail for ground-water resources management alternatives. Improvements in the definition of the flow system were made possible by the acquisition of additional data in the area and by recently completed regional models that include the area. The model was initially calibrated by using the estimated predevelopment potentiometric surface of 1880. The flow system under predevelopment conditions was sluggish and only 100 cubic feet per second (65 million gallons per day) flowed through the model area. It was then tested for acceptance by using the May 1980 potentiometric surface and corresponding pumping stress of approximately 85 million gallons per day in the Savannah, Georgia-Hilton Head Island, South Carolina, area. The flow through the system under 1980 conditions was about 390 cubic feet per second (250 million gallons per day) and the vertical inflow from the overlying surficial aquifer more than doubled due to formerly rejected recharge that now flows vertically into the aquifer. Calibration was accurate + or - 10 feet. The absolute error per node was 3.4 feet. A hypothetical 25-percent increase in pumpage over the entire area was used to represent a gradual growth in commercial and municipal pumpage over the next 20 to 30 years. The increase produced a maximum decline of 30 feet below the existing water level of 135 feet below sea level at the center of the cone of depression in Savannah, and a 5-foot decline at a radius of 20 miles from the center of the cone of depression. (USGS)

Georgia↗