This digital product contains gridded estimates of water-table (wt) elevation and depth to water (dtw) under dry, normal, and wet conditions for New Castle County, Delaware excluding the Piedmont. Files containing the point data used to create the grids are also included. This work is the final component of a larger effort to provide estimates of water-table elevations and depths to water for the Coastal Plain portion of Delaware. Mapping was supported by the Delaware Department of Natural Resources and Environmental Control and the Delaware Geological Survey.
These grids were produced with the same multiple linear regression (MLR) method as Andres and Martin (2005). Briefly, this method consists of: identifying dry, normal, and wet periods from long-term observation well data (Db24-01, Hb14-01); estimating a minimum water table (Sepulveda, 2002) by fitting a localized polynomial surface to elevations of surface water features (e.g., streams, swamps, and marshes); and, computing a second variable in the regression from water levels observed in wells. Separate MLR equations were determined for dry, normal, and wet periods and these equations were used in ArcMap v.9 (ESRI, 2004) to estimate grids of water-table elevations and depths to water. New Castle County was divided into a northern section and a southern section with the C&D Canal being the natural line of demarcation. A minimum water-table surface was then calculated for both the northern and southern sections of New Castle County. However, dividing the county, as well as the water-level data, into two sections did not result in sufficient regression coefficients for use in the estimation process. Therefore, the data (minimum water-table surface and water-level data) were merged together and the water-table elevation and depth to water grids for dry, normal, and wet conditions were then calculated for the county as a whole.
WMS URL: http://maps.dgs.udel.edu/fcgi-bin/de_watertable?
Layer Names: de_dry_dtw, de_norm_dtw, de_wet_dtw, de_dry_wtelev, de_norm_wtelev, de_wet_wtelev
Please give proper credit to the Delaware Geological Survey.
The grids have 30-m horizontal and 1-ft vertical resolutions. Horizontal units are in meters and vertical units are in feet. In the accompanying digital data, grid world files and ground-water level observation data are in the UTM-18N, 1983 projection in meters and elevations are in feet, NAVD 1988. Files are in ESRI, Inc., grid and TIF formats.
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