This map shows the distribution of geologic units found at or near land surface. These units support agriculture and development, are mined for sand and gravel resources, and are the surface-to-subsurface pathway for water. Previous maps and reports covering the same of adjacent areas have focused on hydrogeology (Andres, 1994), surficial geology on a regional basis (Jordan, 1964, 1974; Owens and Denny, 1979, 1986; Denny et al., 1979; Ramsey and Schenck, 199), or subsurface geology (Hansen, 1981; Andres, 1986).
Digital watershed and bay polygons for use in geographic information systems were created for Rehoboth Bay, Indian River, and Indian River Bay in southeastern Delaware. Polygons were created using a hierarchical classification scheme and a consistent, documented methodology that enables unambiguous calculations of watershed and bay surface areas within a geographic information system. The watershed boundaries were delineated on 1:24,000-scale topographic maps. The resultant polygons represent the entire watersheds for these water bodies, with four hierarchical levels based on surface area. Bay boundaries were delineated by adding attributes to existing polygons representing water and marsh in U.S. Geological Survey Digital Line Graphs of 1:24,000-scale topographic maps and by dissolving the boundaries between polygons with similar attributes. The hierarchy of bays incorporates three different definitions of the coastline: the boundary between open water and land, a simplified version of that boundary, and the upland-lowland boundary. The polygon layers are supplied in a geodatabase format.
These vector and raster data sets contain the rock unit polygons for the surficial geology in the Delaware Coastal Plain covered by DGS Geologic Map No. 11 (Milton-Ellendale area) in ESRI shapefile and TIF format.
These raster and vector datasets contains the rock unit polygons for DGS Geologic Map No. 9 (Seaford). This map shows the distribution of geologic units found at or near land surface.
These vector and raster data sets contain the rock unit polygons for the surficial geology in ESRI shapefile and TIF format for the Delaware Coastal Plain covered by DGS Geologic Map No. 12 (Lewes-Cape Henlopen area).
This report deals with fluctuations in nine observation wells during the period 1960 - 1966. These wells are part of a state-wide ground-water monitoring network and are located in areas of little or no pumping. Eight of the wells respond to water-table conditions; the ninth well appears to reflect artesian conditions.
Although precipitation throughout Delaware was generally below average during the period covered by this report, annual average water levels declined very little in the wells reported on here. There is some evidence, however, for a lowering of water-table levels by three to four feet during the period 1960 - 1962.
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.