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ItemAges Of The Bethany, Beaverdam, And Omar Formations Of Southern Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1990-02) Groot, J.J.; Ramsey, K.W.; Wehmiller, John F.The microflora of the Bethany formation and the lower part of the Beaverdam Formation is characterized by a Quercus-Carya assemblage, very few non-arboreal pollen, and Pterocarya and Sciadopitys as exotic constituents. This assemblage has much in common with that of the Brandywine Formation of Maryland and the Eastover Formation of Virginia which are of late Miocene or early Pliocene age. The environment of deposition of the Bethany was probably deltaic, and that of the lower Beaverdam fluviatile. ItemAnalysis And Summary Of Water-Table Maps For The Delaware Coastal Plain(Newark, DE: Delaware Geological Survey, University of Delaware, 2008) Martin, M.J.; Andres, A.S.A multiple linear regression method was used to estimate water-table elevations under dry, normal, and wet conditions for the Coastal Plain of Delaware. The variables used in the regression are elevation of an initial water table and depth to the initial water table from land surface. The initial water table is computed from a local polynomial regression of elevations of surface-water features. Correlation coefficients from the multiple linear regression estimation account for more than 90 percent of the variability observed in ground-water level data. The estimated water table is presented in raster format as GIS-ready grids with 30-m horizontal (~98 ft) and 0.305-m (1 ft) vertical resolutions. Water-table elevation and depth are key facets in many engineering, hydrogeologic, and environmental management and regulatory decisions. Depth to water is an important factor in risk assessments, site assessments, evaluation of permit compliance data, registration of pesticides, and determining acceptable pesticide application rates. Water-table elevations are used to compute ground-water flow directions and, along with information about aquifer properties (e.g., hydraulic conductivity and porosity), are used to compute ground-water flow velocities. Therefore, obtaining an accurate representation of the water table is also crucial to the success of many hydrologic modeling efforts. Water-table elevations can also be estimated from simple linear regression on elevations of either land surface or initial water table. The goodness-of-fits of elevations estimated from these surfaces are similar to that of multiple linear regression. Visual analysis of the distributions of the differences between observed and estimated water elevations (residuals) shows that the multiple linear regression-derived surfaces better fit observations than do surfaces estimated by simple linear regression. ItemApplication Of Geophysics To Highway Design In The Piedmont Of Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1971-06) Woodruff, K.D.The feasibility of using geophysical techniques in determining the amount of overburden and the nature of the subsurface along a proposed highway was tested in the Piedmont area of Delaware. The area is underlain by crystalline rocks capped by varying amounts of unconsolidated material or regolith. Seismic refraction and surface resistivity methods were used at selected stations and the interpretations were later compared to results from test holes and to the material exposed in road cuts. In general, interpretation of the seismic refraction results compared quite well with test borings and with field observations made after construction was started. Resistivity data were inconclusive in themselves but provided some additional control points when correlated with seismic refraction data. With proper control, it is concluded that such techniques could be useful in the Piedmont of Delaware for highway planning. ItemBedrock Geology Of The Piedmont Of Delaware And Adjacent Pennsylvania(Newark, DE: Delaware Geological Survey, University of Delaware, 2000) Plank, M.O.; Schenck, W.S.; Srogi, L.A.This report accompanies a new map that revises the original bedrock geologic maps of the Delaware Piedmont compiled by Woodruff and Thompson and published by the Delaware Geological Survey (DGS) in 1972 and 1975. Combined detailed mapping, petrography, geochemistry, and U-Pb geochronology have allowed us to redefine two rock units and formally recognize eleven new units. A section of the Pennsylvania Piedmont is included on the new map to show the entire extent of the Mill Creek Nappe and the Arden Plutonic Supersuite. ItemThe Cat Hill Formation And Bethany Formation Of Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2004) Andres, A.S.Because of the rapid development occurring in coastal Delaware and the importance of ground water to the economy of the area, definition of formal lithostratigraphic units hosting aquifers and confining beds serves a useful purpose for resource managers, researchers, and consultants working in the area. The Pocomoke and Manokin are artesian aquifers pumped by hundreds of domestic and dozens of public wells along the Atlantic coast in Delaware and Maryland. These aquifers are being increasingly used for public water supply. Two formal lithostratigraphic units, the Cat Hill Formation and Bethany Formation, are established to supercede the Manokin formation and Bethany formation, respectively. In Delaware, these lithostratigraphic units host important aquifers—the Manokin, which occurs in the Cat Hill Formation, and the Pocomoke, which occurs in the Bethany Formation. Composite stratotypes of these units are identified in five drillholes located near Bethany Beach, Delaware. ItemCharacterization of Tidal Wetland Inundation in the Murderkill Estuary(Newark, DE: Delaware Geological Survey, University of Delaware, 2018-03) McKenna, T.E.A parameterization of tidal marsh inundation was developed for the 1,200 hectares of tidal marsh along the 12-km reach of the tidal Murderkill River between Frederica and Bowers Beach in Kent County, Delaware. A parsimonious modeling approach was used that bridges the gap between the simple and often used “bathtub model” (instantaneous inundation based on tides in Delaware Bay), and the more complex modeling of shallow overland that results in the wetting and drying of tidal marshes. For this project, and many other modeling studies that include large areas of marsh, a complex modeling approach of marsh inundation is not warranted due to the lack of data on the dynamics of wetting and drying. A simple parameterization of the wetland inundation process coupled with more complex hydrodynamic and water-quality models can provide sufficient results for estimating the extent of hydrologic and biogeochemical interactions between a marsh and a river. The parameterization can also be used to evaluate anomalies in conservation of water mass and tidal phase offsets that can result from hydrodynamic models that do not explicitly model the dynamic flow and storage of water in tidal wetlands. In the parameterization, the marsh was divided into marsh tracts (n=31) based on hydrologic character and position along the river. A cumulative probability distribution of wetland elevation was calculated for each marsh tract from a digital elevation model. These cumulative probability distributions served as a simplification of the critical information contained in the raster data sets of marsh tracts and elevation. Each marsh tract was related to an adjacent river reach; the area in the tract that was below the stage of its related river reach was instantaneously inundated. Marsh tracts were aggregated into two sets of marsh groups (n=22 and n=4) for analysis and visualization of elevation, hydroperiod, and hydraulic loading. The parameterization was successfully implemented in a collaborative modeling study that created a set of mass loading functions to represent the import and export of chemical species to and from the wetlands. The parameterization was also used to evaluate conservation of water mass and phase offsets in tidal discharge due to the dynamic storage of water in intertidal areas. Marsh elevations had a normal distribution with a mean elevation of 0.72 m and standard deviation of 0.19 m based on analysis of LiDAR data collected for this study. These values have a potential positive bias of 0.1 to 0.2 m resulting from the LiDAR beam not penetrating through the marsh vegetation. Nominal relief on the marsh at the scale of the study area was about 0.6 m (0.4 to 1 m absolute elevation using the NAVD88 datum). From Bowers Beach upstream to Frederica there was a decrease in marsh elevation with the mean elevation decreasing from 0.86 m to 0.60 m. This observation is consistent with measured accretion rates at four sites in the study area that document higher accretion rates upstream near Frederica (0.74 cm/yr) relative to downstream near Bowers (0.33 cm/yr). Upstream marshes are flooded more frequently and for longer duration than downstream marshes so there is more opportunity for accretion to occur. ItemCretaceous And Tertiary Section, Deep Test Well, Greenwood, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1975-06) Talley, J.H.Analyses of drillers' and geophysical logs, cuttings, and 29 core samples from well Nc13-3 near Greenwood, Sussex County, Delaware indicate that the 1500-foot section penetrated by the drill can be divided into seven rock-stratigraphic units: Matawan Formation, Monmouth Formation, unit A, Piney Point Formation, Chesapeake Group (undifferentiated), Staytonville unit, and the Columbia Formation. The rock units are identified on the basis of texture, mineralogy, color, and interpretation of electric and gamma-ray logs. The oldest rocks penetrated are Upper Cretaceous; Tertiary and Quaternary rocks were also encountered. Correlations of the units encountered in the Greenwood test well with subsurface formations in adjacent parts of the Coastal Plain are explored utilizing lithologies, ages, positions in the stratigraphic column, and geophysical characteristics as criteria. Major time boundaries (Cretaceous-Tertiary; Early-Late Paleocene; Paleocene-Eocene; and Eocene-Miocene) are established by a preliminary study of mainly planktonic foraminifera. The Miocene-Pleistocene boundary was determined on changes in lithology across the unconformable contact. ItemThe Cypress Swamp Formation, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2000) Andres, A.S.; Howard, C.S.The Cypress Swamp of Sussex County, Delaware, is underlain by a body of late Pleistocene- to Holocene-age unconsolidated sediments. They form a mappable geologic unit herein named the Cypress Swamp Formation. Deposits of the formation can be found outside the current boundaries of the Cypress Swamp and record the erosion and redistribution of older Pleistocene coastal and Pliocene sedimentary units. ItemDelaware Clay Resources(Newark, DE: Delaware Geological Survey, University of Delaware, 1970-06) Pickett, T.E.Forty-eight samples of Delaware clays were collected and tested jointly by the Delaware Geological Survey and the U. S. Bureau of Mines. Clays potentially useful for face brick are common. The nonmarine Cretaceous Potomac Formation is a potential economic clay at virtually all locations sampled. Some Miocene and Pleistocene clays are also possibilities for brick clays. Other Potomac clays are potential sources for glazed tile, sewer pipe, refractory brick, and stoneware. Coastal marsh clays, frequently containing much organic debris, are potential source material for lightweight aggregate used in lightweight, strong concrete products. Lightweight aggregate has the potential for augmenting dwindling reserves of crushed stone and gravel aggregate. ItemDigital Model Of The Piney Point Aquifer In Kent County, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1979-06) Leahy, P.P.A two-dimensional digital model was developed to simulate the effects of increased pumping on the Piney Point aquifer in Kent County, Delaware. The calibrated digital model was used to predict water-level declines as the aquifer responded to both changes in the distribution and increases in the quantity of pumping to the year 2000. ItemEarthquakes In Delaware And Nearby Areas, June 1973 - June 1984(Newark, DE: Delaware Geological Survey, University of Delaware, 1984-07) Woodruff, K.D.Earthquakes in Delaware and surrounding areas have been well documented historically since about the early 1700’s and since 1972 by instrumental records. Most of the Delaware events have occurred in the Wilmington area immediately adjacent to or within rocks of the Wilmington Complex. Since the compilation of earthquakes by Jordan and others (1974) which lists events through May 1974, six felt earthquakes have occurred in northern Delaware and about 20 additional events in Delaware have been recorded on seismographs of the Delaware Geological Survey. Four of the felt events took place from November 1983 through February 1984 and ranged from a magnitude 1.5 to 2.9. The highest intensity for this series of earthquakes was a possible V (Modified Mercalli). Epicenters were generally in the north Wilmington area as determined both instrumentally and by felt reports. ItemEffects Of Agricultural Practices And Septic-System Effluent On The Quality Of Water In The Unconfined Aquifer In Parts Of Eastern Sussex County, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1989-06) Denver, J.M.The unconfined aquifer is a major source of water supply in eastern Sussex County, Delaware. It also is an important source of water for surface-water bodies and deeper, confined aquifers. The aquifer consists mainly of permeable sand and gravel; its shallow water table is susceptible to contamination by nitrate and other chemical constituents associated with agricultural practices and effluent from septic systems. ItemEstimate Of Direct Discharge Of Fresh Ground Water To Rehoboth And Indian River Bays(Newark, DE: Delaware Geological Survey, University of Delaware, 1987-06) Andres, A.S.The results of water-budget and flow-net model calculations indicate that the rate of fresh ground-water discharge into Rehoboth and Indian River bays is in the range of 21 to 43 million gallons per day. The estimates should be used only as gross indicators of actual conditions because of data gaps and the simplifying assumptions used in the models. However, the estimated discharge rates are significant and useful studies of the water budget of the Bays. ItemEstimating Evapotranspiration for 2016 Growing Season Using Landsat 8 Data and Metric Model in Sussex County, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2023-08) He, C.; Andres, A.S.; Brinson, K.R.; DeLiberty, T.L.Evapotranspiration (ET) is a major part of the water cycle. Reliable measurements or estimates of ET can greatly improve quantitative forecasts and hindcasts of water demand by crops, horticulture, and natural vegetation, and also help to manage and conserve water resources. Direct measurement of ET requires not only specific devices such as eddy covariance instruments, but also well-trained research personnel to collect accurate data. As a result, a variety of indirect methods for estimating ET have been developed in recent decades. Among them, remote sensing methods have proved cost-effective in providing accurate regional and global coverage of ET. In Sussex County, Delaware’s leading county in crop production, the ET distribution for the 2016 growing season was estimated using the Mapping Evapotranspiration at high Resolution with Internalized Calibration method, an energy-balance based ET mapping tool that utilizes satellite images and weather data. The estimated result was compared with field measurements using an eddy covariance instrument. The total estimated ET during Sussex County’s growing season (May-September) in 2016 accounts for 77 to 87 percent of historical-averaged annual ET in this region. The model-simulated seasonal ET for agricultural land is about 33 percent higher than urban/suburban areas and about 22 percent lower than forested areas. This study shows that when forestlands are converted to urban/suburban uses, significant amounts of water are diverted from ET and are then available to run off and/or infiltrate. Given that urban/suburban land has impervious surfaces in the forms of rooftops, roads, driveways, parking lots, sidewalks, etc., much of the water not lost to the atmosphere through ET presumably becomes part of the surface runoff portion of the water budget, thus underscoring the need for adequate storm-water management systems for urban/suburban lands. The results also imply that the practice of ET-based irrigation scheduling could be valuable in Sussex County and throughout the 20 percent of Delaware farmland that is irrigated. ItemEstimation Of The Water Table For The Inland Bays Watershed, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2005) Andres, A.S.; Martin, M.J.A geographic information system-based study was used to estimate the elevation of the water table in the Inland Bays watershed of Sussex County, Delaware, under dry, normal, and wet conditions. Evaluation of the results from multiple estimation methods indicates that a multiple linear regression method is the most viable tool to estimate the elevation of the regional water table for the Coastal Plain of Delaware. The variables used in the regression are elevation of a minimum water table and depth to the minimum water table from land surface. Minimum water table is computed from a local polynomial regression of elevations of surface water features. Correlation coefficients from the multiple linear regression estimation account for more than 90 percent of the variability observed in ground-water level data. The estimated water table is output as a GIS-ready grid with 30-m (98.43 ft) horizontal and 0.305-m (1 ft) vertical resolutions. ItemEvaluating Impacts of Sea-Level Rise on Groundwater Resources in The Delaware Coastal Plain(Newark, DE: Delaware Geological Survey, University of Delaware, 2023-06) He, C.; McKenna, T.E.Due to low elevation and a shallow water table, the Delaware Bay coast is highly vulnerable to sea-level rise. Numerical simulations of rising sea levels, groundwater flow, and salt transport through year 2100 indicate significant impacts on land use due to a rising water table and localized impacts due to saltwater intrusion in the surficial aquifer. Impacts from changes in watertable depths were defined as the conditions where the water table rose above two critical depths: 0 meters (termed saturation, waterlogging, or inundation) and 0.5 meters (effective rooting depths of major local crops). Scenarios modeled were for 0.5, 1.0, and 1.5 meters rise by year 2100. Simulations used SEAWAT4, a three-dimensional, variable-density groundwater flow model. We constructed synthetic conceptual and numerical models with a single rectangular-shaped watershed with an upland, one river, and bay-parallel and inland salt marshes. Parameters for the models were based on the characteristics of ten Delaware Bay watersheds. We transferred water-table depths from simulations to real-world watersheds by mapping model coordinates to a curvilinear grid system within each watershed, which allowed for comparison of areas adversely impacted by sea-level rise by comparing water-table depths to the critical depths. The simulation results predict that sea-level rise causes significant impacts from a rising water table by year 2100. Over 60 percent of the impacted area in all scenarios was cropland. The model results also indicate that the saltwater front under the riverbed migrates landward as far as 4.8 kilometers from its initial location, but is limited to a small area near and parallel to the river and marsh boundaries. ItemAn Evaluation Of Sand Resources, Atlantic Offshore, Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 2002) McKenna, K.K.; Ramsey, K.W.Lithologic logs from 268 vibracores taken from the Delaware Atlantic offshore were evaluated for sediment type and compatibility with historical beach sediment textures. A model of sand resource evaluation, known as “stack-unit mapping” (Kempton, 1981) was applied to all of the cores, and each core was labeled by its lithology in vertical sequence. The results are shown in detailed maps of the beach-quality sand resources offshore in state and federal waters. Results show significant quantities (approximately 54 million cubic yards) of excellent beach-quality sand sources within the three-mile state limit offshore Indian River Inlet, and within the Inner Platform and Detached Shoal Field geomorphic regions. In federal waters, sand is found on Fenwick Shoal Field and farther offshore Indian River Inlet on the Outer Platform (approximately 43.6 million cubic yards combined). Most of the beach-quality sand resources are believed to be reworked tidal delta deposits of a former Indian River Inlet during periods of lower sea level. Farther south, the resources are accumulations of recent surficial sands of the inner shelf (Detached Shoal Field and Fenwick Shoal Field) showing that the geomorphic region does influence sediment quality. This study found that paleochannels and bathymetry had no relationship to grain size. Multiple cut and fill episodes contributed to the diversity in grain sizes. ItemAn Evaluation Of The Resistivity And Seismic Refraction Techniques In The Search For Pleistocene Channels In Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1967-06) Bonini, W.E.Pleistocene channels along the margins of the Atlantic Coastal Plain are developed in crystalline and Triassic sediments (Bonini and Hickok, 1958), or into the Cretaceous and Tertiary coastal plain sediments (Widmer, 1965). Deposits in these channels consist of sand and gravel with amounts of silt and clay. For example, the Bear area channel is 50 to 70 feet deep and contains up to 30 feet of sand and gravel overlain by sandy clay. Because they are usually more permeable than the older deposits into which the channels are developed, Pleistocene deposits are important in ground water studies for several reasons: (1) where they are thick enough they may be used as aquifers, as in the case of the Bear channel, and (2) these beds can effectively increase the recharge into the underlying aquifers by absorbing precipitation and transmitting the water to them. ItemEvaluation Of The Stream-Gaging Network In Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1998) Doheny, E.J.The stream-gaging network in Delaware is a major component of many types of hydrologic investigations. To ensure that the network is adequate for meeting multiple data needs by a variety of users, it must represent the range of hydrologic conditions and land-use types found in Delaware, and include enough stations to account for hydrologic variability. This report describes the current stream-gaging network in Delaware and provides an evaluation of its representativeness for the State. ItemEvaluation Of The Water Resources Of Delaware(Newark, DE: Delaware Geological Survey, University of Delaware, 1966-03) Baker, W.W.; Varrin, R.D.; Groot, J.J.; Jordan, R.R.At present, Delaware has an abundance of water for the foreseeable future, but is already faced with water problems in some municipalities. These can only be resolved satisfactorily through complete evaluation of the State's water resources and the establishment of a coordinated program of water management.