Prepared in cooperation with the U.S. Department of the Army Environmental and Natural Resources Management Office of the U.S. Army Signal Center and Fort Gordon Geomorphology and Groundwater Origin of Amphitheater- Shaped Gullies at Fort Gordon, Georgia, 2010–2012 Open-File Report 2013–1230 U.S. Department of the Interior U.S. Geological Survey Cover. One of the seven amphitheater-shaped gullies observed at Fort Gordon caused principally by groundwater sapping. To summarize, the sandy surficial sediments and shallow water table were recharged, groundwater flowed laterally along the contact with low permeability marl (yellow-red clay in middle of photograph), and seepage occurred where this geologic contact was exposed at land surface. As seepage continued, either in response to sporadic increases in recharge or con- tinuous, longer-term increases in recharge, sapping moved headward, induced landslides, and resulted in the amphitheater- shaped gully. Photograph by James E. Landmeyer, U.S. Geological Survey. Geomorphology and Groundwater Origin of Amphitheater-Shaped Gullies at Fort Gordon, Georgia, 2010–2012 By James E. Landmeyer and John B. Wellborn Prepared in cooperation with the U.S. Department of the Army Environmental and Natural Resources Management Office of the U.S. Army Signal Center and Fort Gordon Open-File Report 2013–1230 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2013 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS. 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Suggested citation: Landmeyer, J.E., and Wellborn, J.B., 2013, Geomorphology and groundwater origin of amphitheater-shaped gullies at Fort Gordon, Georgia, 2010–2012: U.S. Geological Survey Open-File Report 2013–1230, 19 p. http://pubs.usgs.gov/ of/2013/1230/. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................5 Description of the Study Area ............................................................................................................5 Geology ..........................................................................................................................................5 Hydrogeology................................................................................................................................5 Study Design ...................................................................................................................................................5 Geomorphology of Amphitheater-Shaped Gullies at Fort Gordon .........................................................8 Range Road and 8th Street Gully .........................................................................................................8 9th Avenue and 10th Street Gullies .....................................................................................................10 13th Avenue and 15th Street Gully ......................................................................................................12 Range Road and North Range Road Gullies ...................................................................................12 Amphitheater-Shaped Gully Formation and Groundwater Sapping at Fort Gordon .........................14 Potential Preservation of Amphitheater-Shaped Gullies at Fort Gordon .................................................16 Assumptions and Limitations .....................................................................................................................17 Summary........................................................................................................................................................17 Acknowledgments .......................................................................................................................................17 References Cited..........................................................................................................................................17 Figures 1. Photograph showing erosion of surficial soil by rain-drop impact near the cantonment area, Fort Gordon, Georgia, 2012 .........................................................................2 2. Photograph showing amphitheater-shaped gullies caused by relic groundwater seepage, Colorado Plateau, United States ...............................................................................3 3. Photograph showing amphitheater-shaped gully caused by past groundwater seepage, Inner Coastal Plain sediments, Peachtree Rock Heritage Area, Lexington County, South Carolina .................................................................................................................4 4. Photograph showing amphitheater-shaped gully caused by past and current groundwater seepage, Inner Coastal Plain sediments, west of McBee, South Carolina ...............................................................................................................................4 5. Map showing location of Fort Gordon and the generalized locations of the amphitheater-shaped gullies, Richmond, Columbia, Jefferson, and McDuffie Counties, Georgia, 2012 ...............................................................................................................6 6. Generalized correlation of Coastal Plain geologic and hydrogeologic units in east-central Georgia ....................................................................................................................7 7. Map showing location of amphitheater-shaped gully (Gully 1) near Range Road and 8th Street, Fort Gordon, Georgia ..........................................................................................9 8. Aerial photograph showing the amphitheater-shaped gully (Gully 1) near Range Road and 8th Street, Fort Gordon, Georgia ..............................................................................10 9. Map showing location of amphitheater-shaped gullies (Gully 2) near 9th Avenue and 10th Street, Fort Gordon, Georgia ......................................................................................11 10. Aerial photograph showing the amphitheater-shaped gullies (Gully 2) near 9th Avenue and 10th Street, Fort Gordon, Georgia .......................................................................12 iv 11. Map showing location of amphitheater-shaped gully (Gully 3) near 13th Avenue and 15th Street, Fort Gordon, Georgia ................................................................13 12. Aerial photograph showing the amphitheater-shaped gully (Gully 3) near 13th Avenue and 15th Street, Fort Gordon, Georgia ................................................................14 13. Map showing location of amphitheater-shaped gullies (Gullies 4–7) near Range Road and North Range Road, Fort Gordon, Georgia ................................................15 14. Aerial photograph showing the amphitheater-shaped gullies (Gullies 4–7) near Range Road and North Range Road, Fort Gordon, Georgia .......................................16 Table 1. Identification, location, latitude, longitude, and measurement of topographic features related to erosion at each of seven amphitheater-shaped gullies, Fort Gordon, Georgia, 2010–2012. ...............................................................................................8 v Conversion Factors Inch/Pound to SI Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area acre 4,047 square meter (m2) acre 43,560 square feet (ft2) Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29). Altitude, as used in this report, refers to distance above the vertical datum. Abbreviations BP Before present DOD Department of Defense DOI Department of the Interior GIS geographic information system GPS global positioning system LiDAR Light Detection and Ranging NRCS Natural Resources Conservation Service SC South Carolina SCS Soil Conservation Service SES Soil Erosion Service SWCD Soil and Water Conservation District U.S. United States USDA U.S. Department of Agriculture USGS U.S. Geological Survey Geomorphology and Groundwater Origin of Amphitheater- Shaped Gullies at Fort Gordon, Georgia, 2010–2012 By James E. Landmeyer