DERIVATIVE DIGITAL GEOLOGIC MAPS USEFUL FOR ASSESSMENT OF GEOLOGICAL HAZARDS IN THE UPPER COASTAL PLAIN OF GEORGIA

The Georgia Geologic Survey (GGS) has mapped 25 7.5 minute quadrangles in the Upper Coastal Plain of southwestern Georgia during the past seven years as part of the U.S. Geological Survey's STATEMAP program. Sediments consist of Upper Cretaceous to Tertiary sands, sandstones, clays, and limestones. Geological hazards are mainly related to the sands and clays. Storm runoff from highway culverts or poor irrigation practices can lead to significant and rapid erosion of the soft sands. Erosion may threaten agricultural fields and infrastructures such as roads, railroads, pipelines and power lines. Clays underlying unpaved roads can suddenly become slick and severely rutted when wet, and may lead to vehicular accidents. Mapping defined the distribution of those stratigraphic units that are composed of soft sands or clays. Digital GIS technology allows development of derivative maps that highlight these stratigraphic units, and these maps may be combined with digital coverages of infrastructures to focus on areas or points that geological hazards may threaten infrastructures. These derivative maps may be useful for planning routes of future infrastructures or timing of construction. Careful planning and use of these derivative maps could have saved construction costs and facilitated completion of a highway project delayed by frequent and heavy rainfall where a clay-rich residuum of the Clayton Formation was encountered. These sediments are important aquifers for much of Georgia's Coastal Plain. Derivative geologic maps can highlight these units in relation to existing or proposed landfill sites, and can be used to prevent or remediate these sites from becoming geologically related hazards.