INVESTIGATION OF FLOW LOSSES IN THE CAPE FEAR RIVER BETWEEN B. EVERETT JORDAN LAKE AND LILLINGTON, NORTH CAROLINA: A GROUNDWATER PERSPECTIVE

Historical streamflow record collected at a long-term U.S. Geological Survey gaging station located on the Cape Fear River at Lillington, North Carolina (Station 02102500), about 40 kilometers downstream from B. Everett Jordan Lake dam, indicates that the Cape Fear River may be losing water during periods of low flow. The hydrology of the Cape Fear River between B. Everett Jordan Lake dam and Lillington in Lee, Chatham, and Harnett Counties, North Carolina is being investigated by the U.S. Geological Survey to determine the underlying cause of this apparent flow loss. During the spring of 2009, a magnetometer survey was conducted along the 40-kilometer reach to locate impermeable diabase dikes that may divert groundwater discharge. Six sets of synoptic flow measurements were collected from April through October 2009 at 25 locations to target areas where flow loss to the groundwater system may occur. Continuous distributed temperature measurements were collected over a 3-day period in August 2009 in a 500-meter reach at one location where potential diabase dikes were mapped, and synoptic measurements indicated possible flow loss in the river. Near stream groundwater-surface water exchange within the middle and lower part of the 40-kilometer reach was examined from October 2009 through September 2010 by monitoring water level, temperature, and water quality in piezometer transects completed within floodplain sediments and soils. An airborne infrared thermographic survey of the 40-kilometer reach was flown in February 2010 to locate groundwater seeps along the river bank under high water table conditions.

Preliminary data and analyses will be presented, with discussion focusing on groundwater conditions and groundwater-surface-water interaction in the upper Cape Fear River basin in 2009 and 2010.