The Columbia deposits of Delaware form a sheet of sand with a maximum thickness of approximately 150 feet which covers most of the Coastal Plain portion of the State. The dispersal pattern, deduced from foreset dip directions of cross-bedding, indicates that the sediment entered the study area from the northeast, i.e., from the direction of the valley of the Delaware River between Wilmington and Trenton, and spread south and southeast over Delaware.
Sussex County is in the Atlantic Coastal Plain. Its relatively flat, featureless topography is characterized by two terrace-like surfaces; the lower one rises from sea level to about 40 feet above sea level, and the higher one rises inland from 40 to about 60 feet above sea level. Peculiar landforms of low relief, broad ovals, similar to the "Carolina bays," and to the "New Jersey basins" are common on the sandy flat divides in Sussex County. Hydrologically, they are sites of much ground-water discharge, by evapotranspiration, from meadow and marsh of lush vegetation.
Delaware has an abundant supply of ground water of a quality suitable for most purposes. About 30 million gallons of water a day was pumped from the ground in 1954. It is estimated that this is roughly 1/16 of the optimum yield. This water is derived from nine groups or series of water-bearing units and is obtained from wells which yield as much as 1,100 gallons per minute. Thousands of wells serve agriculture, industry, municipalities, and domestic users. Geographically, Delaware is situated along the Atlantic coast of the United States in two physiographic provinces: the Piedmont and the Coastal Plain. The Piedmont is a belt of rolling foothills of the Appalachian Mountains. It is separated from the Coastal Plain by the Fall Line, a narrow zone of rapids or falls along which rivers and creek descend rapidly from the mature valleys of the Piedmont to the sluggish tidal estuaries of the coastal area. The Coastal Plain is a flat or gently undulating plain of relatively low altitude, which borders the Atlantic Ocean and its estuarine embayments.
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.
Geophysical logging techniques have been used in Delaware for many years as a means of identification and correlation of Coastal Plain formations. Criteria for the recognition of those formations having distinctive types of logs are presented. Formation factors have been calculated using multiple-point resistivity logs, temperature logs, and ground-water quality data and range from 1.2 to 6.8 for various formations underlying the State. Formation factors in turn are used to estimate water quality in later test holes.
Beaverdam Branch, the Nanticoke River, Sowbridge Branch, and Stockley Branch drain small basins in the Delaware Coastal Plain that are characterized by similar climate, topography, geology, and land use. Withdrawals of ground water and surface water are very small, there is little urbanization, and other man-made effects, which include minor regulation on Sowbridge Branch and construction of drainage ditches in the Nanticoke basin, probably have had minimal effect on the natural hydrologic regimen. These are virtually natural-flow streams, which, because of similar basin characteristics, have nearly identical rates of evapotranspiration and runoff. During the 10-year period, 1959-68, precipitation averaged 40-42 inches annually, runoff averaged 16-17 inches annually, and evapotranspiration averaged 23-25 inches annually.
Delaware’s oldest rocks are metamorphic crystalline rocks of the central Appalachian Piedmont Physiographic Province. Atlantic Coastal Plain sediments overlie the crystalline rocks of the Piedmont and range in thickness from a feather edge at the Fall Line to approximately 9,000 feet in the southeastern corner of Delaware. Sediments range in age from Early Cretaceous to Holocene.
The shaded relief image on the left was created using 30-meter resolution Digital Elevation Models (DEMs). The DEMs were developed by John Mackenzie, University of Delaware College of Agriculture and Natural Resources Spatial Analysis Laboratory, from rasterized 1992-93 United States Geological Survey (USGS) Digital Line Graph (DLG) hypsography data. He also combined these data with zero-elevation contours extracted from 1989 Landsat TM Band 7 satellite imagery for coastal quadrangles. The image was digitally enhanced using a false sun angle of 45 degrees shining from the northwest to exaggerate the geomorphic features. In reality the Delaware Coastal Plain is not "mountainous," as it looks in this enhanced image. The hydrology layer was created using USGS 30 x 60 minute and 7.5 minute series DLG data. Municipal boundaries were created using the Delaware Municipal Boundary Framework Layer. Both maps are projected in Universal Transverse Mercator, Zone 18 (UTM 18) on the North American Datum 1983 (NAD83).
Emphasis is placed herein on the years of Dr. Groot's leadership of the Survey. The remarkable work of James C. Booth in the last century is acknowledged but has elsewhere been entered in history. Some continuing activities of the Survey after 1969 are noted together with comments of an experienced observer; this current period may someday receive the attention of a recorder having the enhanced perspective of time.
The following report of the geological survey of the state of Delaware, conducted in the years 1837 and 1838, embraces all the observations and examinations which were made during the continuance of the survey, including those contained in the first and second annual reports, already laid before the legislature.
In order to obtain sufficient data which will enable the State to develop its water resources to the fullest extent of which they are capable, a series of systematic investigations is necessary. A long-range plan describing these studies is the subject of this report. A brief discussion of water in Delaware is presented first to provide a proper background for the long-range plan. The plan itself merely outlines the overall objectives and types of investigational work that must be pursued if the State is to develop its water resources wisely.
This is a brief story about water and the ways in which the Delaware Geological Survey helps insure that you will always have a plentiful supply of this precious natural resource.
This guide contains illustrations of fossils from Delaware Geological Survey Bulletin No. 3 ("Marine Upper Cretaceous Formations of the Chesapeake and Delaware Canal") and Report of Investigations No. 7 ("An Invertebrate Fauna from the Upper Cretaceous of Delaware"). The identifications have been revised to be as accurate as possible so that this guide will be useful to those fossil collectors interested in classifying their "finds."
The need for locating additional sources of ground water for the Delaware Atlantic seashore, a predominantly recreation-oriented area, is indicated by an expanding population in the belt between Philadelphia, Pennsylvania and Washington, D.C., combined with increasing leisure time. Present water use in the shore area is approximately 4 million gallons per day and will reach 9.3 million gallons per day by the year 2000. A new geologic interpretation of the occurrence of deep aquifers in the Delaware Atlantic seashore area is presented. Recent data from deep wells has enabled the construction of a more accurate geologic framework upon which the hydrologic data are superimposed. Correlation of Miocene sands concludes that the Manokin aquifer lies at greater depths in southeastern Delaware than previously thought.
Geology and hydrology of the Wilmington, Delaware area. There are 4 sheets in this series.