Geology topics
Keith R. Prince
Publications and source records attributed to Keith R. Prince.
U.S. Geological Survey Subsidence Interest Group Conference; proceedings of the Technical Meeting, Las Vegas, Nevada, February 14-16, 1995
Introduction to Papers: This report is a compilation of short papers that are based on oral presentations summarizing the results of recent research that were given at the third meeting of the Subsidence Interest Group held in Las Vegas, Nevada, February 14-16, 1995. The report includes case studies of land subsidence and aquifer-system deformation resulting from fluid withdrawal, geothermal development, and mine collapse. Methods for monitoring land subsidence using Global Positioning System technology for the rapid and accurate measurement of changes in land-surface altitude also are described. The current status of numerical simulation of land subsidence in the USGS is summarized, and several of the short papers deal with the development and application of new numerical techniques for simulation and quantification of aquifer system deformation. Not all oral presentations made at the meeting are documented in this report. Several of the presentations were of ongoing research and as such, the findings were provisional in nature and were offered at the meeting to stimulate scientific discussion and debate among colleagues. The information presented in this report, although only a subset of the proceedings of the meeting in Las Vegas, should help expand the scientific basis for management decisions to mitigate or control the effects of land subsidence. The short papers describing the results of these studies provide a cross section of ongoing research in aquifer mechanics and land subsidence and also form an assessment of the current technology and 'state of the science.' The analytical and interpretive methods described in this report will be useful to scientists involved in studies of ground-water hydraulics and aquifer-system deformation.
Quantitative assessment of the shallow ground-water flow system associated with Connetquot Brook, Long Island, New York
Streamflow on Long Island is derived principally from shallow ground water that flows above the deeper regional flow system. The movement of shallow ground water was studied during 1975-82 at Connetquot Brook, an undisturbed stream in Connetquot River State Park, in south-central Long Island, New York. The investigation encompassed (1) field studies of streamflow, ground-water levels, and age of water as indicated by tritium and dissolved-oxygen concentrations and (2) numerical simulation of the shallow flow system to evaluate the hydraulic factors that govern the direction of shallow ground-water flow near and beneath the stream. Analysis of water-level data indicates that ground water flows essentially horizontally throughout the drainage basin except near and beneath the stream, where it moves vertically upward toward the stream discharge boundary. Water levels in wells driven directly into the streambed and into the streambank at three sites were 1 to 2 feet higher than stream stage in the first 5 feet of penetration. Increases in head, which were detected to depths of 30 feet beneath the streambed, indicate upward movement of water above that depth. Hydraulic conductivity of the streambed sediments was calculated from head gradients in the streambed and from measured stream seepage; values were between 11 and 15 feet per day. Water samples from selected wells were analyzed for dissolved-oxygen and tritium concentrations to determine the relative age of the water in an attempt to locate the bottom boundary of the shallow flow system. Dissolved oxygen showed no pattern, but tritium concentrations about 1,000 feet from the stream were lower than those near the stream. The tritium concentrations indicate that the lower flow boundary was between 45 and 100 feet below the water table. A two-dimensional cross-sectional flow model of the shallow flow system was developed. The near-stream model response compared well with field data when the streambed discharge boundary was simulated as a uniform leaky bed. A systematic sensitivity analysis was done to determine which factors have the greatest influence on hydraulic head in the system. Ten dimensional parameters that describe the important aspects of the flow system were combined into a series of dimensionless parameters to simplify analysis. Results indicate that (1) streambed factors (width and hydraulic conductivity) are most influential upon heads near the stream, (2) factors representing thickness of the shallow flow system influence heads distant from the stream but have a negligible effect near the stream, and (3) factors that represent the quantity of water entering the system (recharge) influence the heads throughout the area. Field measurements of hydraulic head indicate that the thickness of the shallow flow system below the stream channel is about 30 feet. However, results of the sensitivity analysis indicate that the shallow system's thickness has a negligible effect on head distribution beneath the stream.
Streamflow augmentation at Fosters Brook, Long Island, New York — A hydraulic feasibility study
A 27-day streamflow augmentation test was conducted in December 1979 at Fosters Brook, near the south shore of Long Island, to investigate the hydraulic feasibility of pumping ground water to supply flow to an ephemeral stream during dry periods. Measurements of soil moisture in the unsaturated zone beneath the streambed indicate that infiltration rate and soil-moisture content are interrelated. Initial infiltration was measured with a neutron logger; the wetting front traversed the unsaturated zone at an average of 11.2 inches per hour and reached the water table in 5.5 hours. Soil moisture in the unsaturated zone ranged from 20 percent at the start of the test to nearly 41 percent, nearly the saturation point, 20 days later. Stream discharge was measured at four sites along the stream channel, and the augmentation rate was monitored continuously at the starting point. Infiltration rates increased steadily in all reaches during the first 12 days of the test, but from the 12th to the 20th day, when discharge was increased by 50 percent, infiltration rates decreased along the two upstream reaches but continued to increase along the three downstream reaches. Infiltration rates remained constant from days 20 through 26. During the first 24 hours of the test, the stream reached a maximum length of 2,050 feet, but after 13 days, it had shortened to 1,300 feet as a result of seepage losses. The relationship between discharge and stream length was linear within the range of discharge investigated (0.54-1.63 cubic feet per second). Ground-water levels rose in response to flow augmentation and reached a maximum rise of about 6.5 feet in a well situated 14 feet from the center of the streambed and 225 feet downstream from the start of the flow. Measured water-level response was compared to levels predicted by a one-dimensional analytical model and a three-dimensional mathematical model; results indicate that ground-water response is determined principally by streambed characteristics and soil-moisture content in the unsaturated zone. Variations in water temperature and in streambed composition had significant effects upon infiltration rates. Changes in water temperature, amount of vegetation, soil-moisture content, and stream stage, combined with local variations in streambed permeability and aquifer conductivity, make accurate prediction of seepage rates virtually impossible at present. Data from this study suggest that site-specific investigations are necessary wherever streamflow augmentation is planned.
Use of flow-duration curves to evaluate effects of urbanization on streamflow patterns on Long Island, New York
Streamflow patterns on Long Island, N.Y., have been changing over the last three decades in response to eastward population growth and urbanization. Flow-duration curves for nine streams in Nassau and Suffolk Counties indicate that, during this time, streams in urbanized areas have had increased peak flows and decreased base flows, whereas streams in sparsely populated areas have shown little or no change. The increase in peak flows reflects the greater volume of storm runoff from impermeable surfaces such as roads, parking lots, and roofs. The decrease in base flows results from the lowering of groundwater levels, principally by sanitary sewerage and extensive pumping for public water supply. At East Meadow Brook, in a sewered, densely populated area of Nassau County, peak flows (1-percent duration) increased by 41% during 1946-74, and base flows (98-percent duration) decreased by 99%. In contrast, peak and base flows of Carmans River, in a largely undisturbed, rural area of Suffolk County, showed fluctuations no greater than 19% during the same period. (USGS)
Potentiometric surface of the Lloyd aquifer on Long Island, New York, in January 1975
A map showing the potentiometric surface of the Lloyd aquifer was drawn from water-level measurements made in January 1975. Altitude of the potentiometric surface ranged from more than 20 feet below mean sea level in Queens County to more than 40 feet above mean sea level in Suffolk County.