Ground water flow analysis of a mid-Atlantic outer coastal plain watershed, Virginia, U.S.A

Models for ground water flow (MODFLOW) and particle tracking (MODPATH) were used to determine ground water flow patterns, principal ground water discharge and recharge zones, and estimates of ground water travel times in an unconfined ground water system of an outer coastal plain watershed on the Delmarva Peninsula, Virginia. By coupling recharge and discharge zones within the watershed, flowpath analysis can provide a method to locate and implement specific management strategies within a watershed to reduce ground water nitrogen loading to surface water. A monitoring well network was installed in Eyreville Creek watershed, a first-order creek, to determine hydraulic conductivities and spatial and temporal variations in hydraulic heads for use in model calibration. Ground water flow patterns indicated the convergence of flow along the four surface water features of the watershed; primary discharge areas were in the nontidal portions of the watershed. Ground water recharge zones corresponded to the surface water features with minimal development of a regional ground water system. Predicted ground water velocities varied between < 0.01 to 0.24 m/day, with elevated values associated with discharge areas and areas of convergence along surface water features. Some ground water residence times exceeded 100 years, although average residence times ranged between 16 and 21 years; approximately 95% of the ground water resource would reflect land use activities within the last 50 years.     

The applicability of the Florida mandatory endorsement for sinkhole collapse coverage. Part I. Legal aspects

Florida statute §627 706 was enacted to provide sinkhole collapse coverage The legislative intent of the Statute was to protect the property owner from the unexpected damage to structures and personal property arising from the occurrence of sinkholes However, since the Statute was enacted, litigation involving considerable expense to the insurance companies and property owners has occurred because of various interpretations of the Statute The technical and legal interpretations do not appear always to be the same. This article discusses some of the interpretations accepted by the court, and it addresses the role of the engineer, geologist, and hydrologist in the technical interpretations of the Statute. In an attempt to reduce litigation and associated court costs, recommendations are made to resolve some of the vagueness and ambiguities in the Statute and still maintain the Statute's flexibility and intent to protect public welfare     

The relationship of wind stress to heat flux divergence of Texas-Louisiana shelf waters

Monthly, multi-annual mean heat budgets are calculated for waters overlying the Texas-Louisiana shelf. Heat storage rates are calculated on the basis of a volumetric temperature-salinity census; unpublished data from Bunker are consulted to determine surface heat exchanges. Monthly heat flux divergences, calculated as residuals in the heat budget equation, show divergence of heat during the months of June and July, the upwelling season for much of the Texas-Louisiana coast, and convergence of heat during the rest of the year when winds conducive to downwelling prevail.     

MODAL ANALYSIS OF AIRPHOTO LINEARS,CENTRAL IDAHO

Approximately 3,000 airphoto linears from an 8,300 km² area of central Idaho are plotted, classified for azimuthal orientation, counted for frequency, and measured for length. Dominant linear orientations, weighted for length, are compared to equivalent central tendency measures for joints, dikes, and foliation. Variations in linear density are also compared to differing lithologies. Statistical analysis reveals the following: (1) the dominant lineation mode is statistically independent of the dominant foliation mode; (2) no statistically significant difference exists between the dominant lineation mode and the average directional mode of dikes; (3) no statistically significant difference exists between the dominant lineation mode and the average directional mode of joints; (4) linear frequency is statistically independent of lithology. Visual comparison of raised relief maps with the isopleth map of directionally dominant linears reveals a pronounced correspondence between those areas exhibiting strong structural control over landforms and highs on the isopleth surface.     

Modern sedimentology and hydrology of Lake Manitoba,Canada

Lake Manitoba, North America's thirteenth largest lake, occupies a glacier-scoured basin in south-central Manitoba. Despite its large size, the lake is extremely shallow with a mean depth of 4.5 m. The lake can be subdivided into two connected but distinctly different basins: a small, irregular-shaped North Basin and a much larger and smoother South Basin. Most of the water inflow is from the Waterhen River (42% of the inflow) and from precipitation directly on the lake's surface (40%), while nearly 60% of the outflow is by evaporation. Lake Manitoba water is alkaline and brackish with the salinity dominated by sodium and chloride ions. The surficial offshore deposits of the main South Basin of the lake consist mainly of silt and clay-sized sediments composed of detrital components (clay minerals, quartz, carbonates, and feldspars) and endogenic/authigenic components (carbonates, sulfides, and organic matter). In addition to these modern sediments, several areas of relict fluvial-shoreline sand and till deposits occur in the South Basin. The lacustrine processes presently operating in Lake Manitoba reflect the influence of (1) the extreme shallow depth of the lake, (2) the basin morphology, and (3) the water chemistry. In addition, land clearing and increased watershed drainage have resulted in substantially increased sedimentation rates in the South Basin during the past century.     

A scientifically based nationwide assessment of groundwater quality in the United States

Beginning in 1986, the U.S. Geological Survey began an effort to develop a National Water-Quality Assessment Program. The basic premise underlying this initiative is that a better understanding of the quality of water resources across the country, both surface- and groundwater, is needed to develop effective programs and policies to meet the nation's water-quality concerns. The program will focus on water-quality conditions that are prevalent or large in scale, such as occur from nonpoint sources of pollution or from a high density of point sources.The design of the program is substantially different from the traditional approach of a diffuse national monitoring network.The major activities of the assessment program will be clustered within a set of hydrologic systems (river basins and aquifer systems), referred to as study units. In aggregate, the study units will account for a large part of the nation's water use and represent a wide range of settings across the country.Unique attributes of the program include: (1) the use of consistent study approaches, field and laboratory methods, water-quality measurements, and ancillary data measurements for all study units; (2) the development of a progressive understanding of water-quality conditions and trends in each study unit through long-term studies that rotate periods of intensive data collection and analysis with periods during which the assessment activities are less intensive; and (3) the focus of considerable effort on synthesizing results from among the study units to provide information on regional and national water-quality issues.Paper presented at 28th International Geological Congress, Washington, D.C., July 10, 1989.