Hydraulic Gradients and Flow Rates in a Shallow Coastal Plain Aquifer 1,2

David D. Bosch, Joseph M. Sheridan, R. Richard Lowrance 3

Abstract

Water-table gradients were measured and saturated flow rates estimated within a small watershed consisting of a tilled upland field and a downslope riparian forest buffer system located in the Gulf-Atlantic Coastal Plain Tifton-Vidalia Uplands. Three years of water-table measurements and estimates of saturated hydraulic conductivity were used to evaluate and quantify saturated water flow directions and rates. Forest treatments consisting of clear cutting, thinning, and no cutting were examined. Groundwater gradients generally followed the land slope, although during summer months hydraulic gradient within the forested buffer reversed. Water-table data indicate the riparian area was saturated from January through March. During this time, flow direction in the shallow aquifer is from the top of the field to the stream bottom. During summer months, high rates of forest evapotranspiration created large water sinks in the shallow subsurface and large hydraulic gradients. Examination of water-table elevations indicates the seasonal water demand of the forest shifts the direction of shallow subsurface aquifer flow. During these periods flow direction within the riparian buffer was from the lowest landscape position to the riparian forest, reversed from winter months.

  1. Contribution from the USDA-ARS, Southeast Watershed Research Laboratory, P.O. Box 946, Tifton, GA 31793, in cooperation with Univ. of Georgia Coastal Plain Exp. Stn.
  2. All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status, or handicap.
  3. Hydraulic Engineer, Hydraulic Engineer, and Ecologist, USDA-ARS, Southeast Watershed Research Laboratory, PO Box 946, Tifton, Georgia 31793.

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