HISTORY OF SEDIMENTATION IN A CATAWBA RIVER RESERVOIR: BROWN'S COVE, LAKE WYLIE, NC

Brown's Cove on Lake Wylie, one of the reservoirs along the Catawba River, has been impacted by sedimentation since completion of the Lake Wylie dam in 1924. The history of sedimentation is reconstructed from historical records, cores, Pb-210 data, and heavy mineral and geochemical analysis. Changing sedimentary processes and rates can be documented using sedimentologic logs and sequence stratigraphy. Initial flooding of Brown's Cove in 1924 produced a transgressive sequence composed dominantly of suspension load. The transgressive sequence continued to accumulate up to 1983. Beginning about 1983, as shown on air photos, a distributary from the advancing delta caused the progradation of a coarsening-upward delta lobe. The coarsening up sequence is composed of turbidites grading up to traction load deposits. The distributary abandoned the delta lobe about 1993 leading to compaction, subsidence and creation of accommodation space. That space was filled by a second transgressive sequence. Another distributary avulsed to the site in 2003 resulting in a second prograding delta lobe. Prior to the 1924 flooding of Brown’s Cove, mafic-rich fluvial sediments from the southern part of the watershed were an important component of the sediment. Between 1983 and 1993, felsic-rich sediments from the recently clear-cut central and northern parts of the watershed became important. The youngest sediments are mafic-rich and likely due to extensive land development in the southern part of the watershed that began in 2004. Three methods of estimating average sedimentation rates for the main part of Brown’s Cove provide comparable results (~1.8 cm/yr). Higher rates of sedimentation (~6 cm/yr) occur in proximal settings where delta lobes actively prograde.