Geologic Controls on Erosion, Sedimentation Of Streams, and Potential for Groundwater Contamination in Southwestern Georgia
Cocker, Mark D.
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The Georgia Geologic Survey (GGS) has mapped 29 7.5 minute quadrangles in the Upper Coastal Plain of southwestern Georgia during the past eight years as part of the U.S. Geological Survey’s STATEMAP program. Exposed sediments in these quadrangles consist of Upper Cretaceous to Tertiary sand, sandstone, clay, and limestone. Two geological rock units, the Eocene-ageClaiborne Group and the Cretaceous Providence Formation consist mainly of sand or soft sandstone that are easily eroded when exposed to concentrated storm runoff. Runoff from highway culverts, poor irrigation or loggingpractices can lead to significant and rapid erosion of the soft sands. Clear-cutting and stripping or burning of fragile ground cover in sandy terrain significantly inhibits regeneration of the ground cover that protects the sand from erosion. Erosion may threaten agricultural fields and infrastructures such as roads, railroads, pipelines and power lines. Sedimentation or silting up of streams by sand eroded from the surrounding terrain reduces the depth and velocity of normal stream flow and adversely affects stream ecology. Gullies resulting from this erosion tend to collect a variety of trash. As the Providence Formation and Claiborne Group are both important local and regional aquifers in the southwestern Coastal Plain of Georgia, trash may leak chemicals into these aquifers and have a detrimental effect on domestic, agricultural, and public water supplies.