Geomorphology and groundwater origin of amphitheater-shaped gullies at Fort Gordon, Georgia, 2010-2012

Abstract

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 continuous, longer-term increases in recharge, sapping moved headward, induced landslides, and resulted in the amphitheatershaped gully. Photograph by James E. Landmeyer, U.S. Geological Survey. 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. Geomorphology and Groundwater Origin ofFor an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. 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 AbstractSeven amphitheater-shaped gullies at valley heads in the northern part of Fort Gordon, Georgia, were identified by personnel from Fort Gordon and the U.S. Geological Survey during a field investigation of environmental contamination near the cantonment area between 2008 and 2010. Between 2010 and 2012, the amphitheater-shaped gullies were photographed, topographic features were surveyed using a global positioning system device, and the extent of erosion was estimated using Light Detection and Ranging imagery. The seven gullies are distributed across a broad area (and most likely are not the only examples) and have a similar geomorphology that includes (1) an amphitheater (semicircular) shaped escarpment at the upgradient end on a plateau of Upper Eocene sands of no readily discernible elevated catchment area or natural surface-water drainage; (2) a narrow, trench-shaped, flatbottomed incisement of low-permeability marl at the downgradient end; and (3) steep-sided valley walls, some formed by landslides. Surface-water runoff is an unlikely cause for the amphitheater-shaped gullies, because each valley has a relatively small drainage area of sandy terrain even at those gullies that have recently received discharge from stormwater drains. Also, presumed high rates of runoff and ...

Groundwater chemistry, hydrogeologic properties, bioremediation potential, and three-dimensional numerical simulation of the sand and gravel aquifer at Naval Air Station Whiting Field, near Milton, Florida, 2015–20

“…The western valley has an average drop in altitude of about 140 ft and is deeply incised by streams and man-made concrete lined ditches that terminate near Clear Creek. These valleys were likely created by headward erosion processes during groundwater sapping, as has been described in other high altitude, well drained coastal plain sediments (Landmeyer and Wellborn, 2013).…”