This digital product contains gridded estimates of water-table (wt) elevation and depth to water (dtw) under dry, normal, and wet conditions for Kent County, Delaware. 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 (Hb14-01, Jd42-03, Mc51-01, Md22-01); 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. A separate MLR equation was 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. Kent County was divided into three regions (south, central, north). A minimum water-table surface was calculated for each of these areas and were merged together to create a single minimum water-table surface for the entire county. This grid was filtered and smoothed to eliminate edge effects that occurred at the boundaries between each of the three regions. Water-table elevation and depth to water grids for dry, normal, and wet conditions were then calculated for the county as a whole.
This data is accessible as a map service on Delaware FirstMap.
Additionally, this and other services are available in the ArcGIS Online DGS Map Viewer
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 TIFF formats. Layer Name Definitions:
- de_dry_dtw = Depth to Water Table in a Dry Year
- de_norm_dtw = Depth to Water Table in a Normal Year
- de_wet_dtw = Depth to Water Table in a Wet Year
- de_dry_welevt = Water Table Elevation in a Dry Year
- de_norm_wtelev = Water Table Elevation in a Normal Year
- de_wet_wtelev = Water Table Elevation in a Wet Year