The USGS, in cooperation with State and local agencies, systematically collects groundwater data at varying measurement frequencies to monitor hydrologic conditions on Long Island, New York. Each year during April and May, the USGS conducts a synoptic survey of water levels to define the spatial distribution of the water table and potentiometric surfaces within the three main aquifers beneath Long Island—the upper glacial, Magothy, and Lloyd—and the hydraulically connected Jameco and North Shore aquifers.
A digital elevation model from the National Elevation Dataset was combined with additional lidar-derived terrain models of Suffolk County and New York City to create a depth-to-water map. A continuous surface of the water table was created in a geographic information system (GIS) environment using an iterative finite difference interpolation technique with measurements from observation and supply wells, streamgages, interpreted 10-foot (3-m) contour intervals, and the coastline. The continuous surface of the water table was adjusted for vertical datum differences across Long Island, and the interpolated surface was then subtracted from the lidar elevation model. The results are shown as a continuous depth-to-water-table map.
This map depicts the depth to the water table beneath Long Island during April–May 2013. Areas in which the depth to the water table is shallow are shown in red and indicate areas where potential substructure flooding may occur.